Method 1611: Enterococci in Water by 

TaqMan®

 Quantitative Polymerase Chain 

Reaction (qPCR) Assay 

 October 2012 
U.S. Environmental Protection Agency 

Office of Water (4303T) 

1200 Pennsylvania Avenue, NW 

Washington, DC 20460 

EPA-821-R-12-008
iii

Acknowledgments

This method was developed under the direction of Rich Haugland, Kevin Oshima and Alfred P. Dufour of 

the U.S. Environmental Protection Agency’s (EPA) Human Exposure Research Division, National 

Exposure Research Laboratory, Cincinnati, Ohio. 

The following laboratories are gratefully acknowledged for their participation in the validation of this 

method in marine and fresh waters: 

Participant Laboratories

Single laboratory validation 

 Mycometrics, LLC: King-Teh Lin and Pi-shiang Lai 

 New York State Department of Health, Environmental Biology Laboratory: Ellen Braun-Howland 

and Stacey Chmura 

Marine ambient water multi-laboratory validation 

 BioVir: Rick Danielson and Rosie Newton 

 EPA Region 1 – New England Regional Laboratory: Jack Paar and Mark Doolittle 

 EPA Region 10 Laboratory: Barry Pepich and Stephanie Harris 

 Hampton Roads Sanitation District: Robin Parnell and Tiffany Elston 

 King County Environmental: Eric Thompson and Joe Clark 

 Mycometrics: King-Teh Lin and Jeff Cook 

 NOAA – AOML/Ocean Chemistry Division: Chris Sinigalliano, David Wanless, and Maribeth 

Gidley 

 NOAA – NOS/Center for Coastal Environmental Health & Biomolecular Research: Janet Gooch 

Moore and Chris Johnston 

 Orange County Public Health Laboratory: Richard Alexander and Joe Guzman 

 Texas A&M University – Corpus Christi: Joanna Mott, Ladonna Henson, Sarah Bortz, and Lindsey 

Myers 

 Virginia Institute of Marine Science: Howard Kator and Kimberly Reece 

Fresh ambient water multi-laboratory validation 

 BioVir: Rick Danielson and Rosie Newton 

 Hampton Roads Sanitation District: Robin Parnell and Tiffany Elston 

 King County Environmental: Eric Thompson and Joe Clark 

 Orange County Public Health Laboratory: Richard Alexander and Joe Guzman 

 Orange County Water District: Donald Phipps and Menu Leddy 

 Scientific Methods Incorporated: Fu-Chih Hsu and Rebecca Wong 

 Texas A&M University – Corpus Christi: Joanna Mott, Ladonna Henson, and Sarah Bortz 

 Texas A&M University – College Station: Suresh Pillai, Palmy Jesudhasan, and Katherine McElhany 

 University of Iowa Hygienic Lab: Nancy Hall, Greg Gingerich, Cathy Lord, and Lucy DesJardin 

 Wisconsin State Lab of Hygiene: Sharon Kluender and Jeremy Olstadt 
iv

Disclaimer

Neither the United States Government nor any of its employees, contractors, or their employees make any 

warranty, expressed or implied, or assumes any legal liability or responsibility for any third party’s use of 

apparatus, product, or process discussed in this method, or represents that its use by such party would not 

infringe on privately owned rights. Mention of trade names or commercial products does not constitute 

endorsement or recommendation for use. 

Questions concerning this method or its application should be addressed to: 

 Robin K. Oshiro 

 Engineering and Analysis Division (4303T) 

 U.S. EPA Office of Water, Office of Science and Technology 

 1200 Pennsylvania Avenue, NW 

 Washington, DC 20460 

oshiro.robin@epa.gov or OSTCWAMethods@epa.gov 

 
v

Introduction

Enterococci are commonly found in the feces of humans and other warm-blooded animals. Although 

these organisms can be persistent in the environment, the presence of enterococci in water is an indication 

of fecal pollution and the possible presence of enteric pathogens. Epidemiological studies have led to the 

development of criteria for promulgating recreational water standards based on established relationships 

between the measured density of enterococci colony forming units (CFU) in the water by culture based 

methods and the risk of gastrointestinal illness (GI) associated with swimming in the water (References 

17.3, 17.6, 17.7, and 17.8). 

Method 1611 describes a quantitative polymerase chain reaction (qPCR) procedure for the detection of 

DNA from enterococci bacteria in ambient water matrices based on the amplification and detection of a 

specific region of the large subunit ribosomal RNA gene (lsrRNA, 23S rRNA) from these organisms. 

The advantage of this method over currently accepted culture methods that require 24 − 48 hours to 

obtain results is its relative rapidity. Results can be obtained by this method in 3 − 4 hours. 

EPA conducted a single-laboratory validation (SLV) study of Method 1611 in marine and fresh water 

matrices, to assess potential matrix issues across multiple fresh and marine water matrices from different 

geographic regions across the U.S. During the SLV thirty-seven volunteer laboratories collected and 

shipped recreational water (marine and/or fresh) samples to the two analytical laboratories for Method 

1611 analyses. For all 25 (each) marine and fresh water matrices, no matrix inhibition was observed for 

Method 1611. EPA then conducted multi-laboratory validation studies to assess method performance and 

reproducibility and develop quantitative quality control (QC) acceptance criteria. 

Results of the multi-laboratory validation studies enabled performance characterization of Method 1611 

in the reference matrix phosphate buffered saline (PBS) and in marine and fresh water matrices. Results 

also enabled the development of initial precision and recovery/ongoing precision and recovery (IPR/OPR) 

and matrix spike (MS) QC acceptance criteria. In addition, results from marine water and fresh water 

samples (5 different sources for each matrix type) spiked with commercially available target organism 

cells were used to assess method reproducibility. 

The highly variable recoveries observed during these studies should be taken into consideration when 

analyzing results from Method 1611. It is recommended that analysts generate standard curves with each 

new lot of qPCR reagents or primers and probes to demonstrate comparable performance with these new 

reagents. In addition, weekly calibrator samples should be monitored to ensure that they are within the 

acceptable range of the methods; if calibrator samples are not within the acceptable range, new calibrator 

samples should be prepared and analyzed. Following these recommendations should increase analyst 

proficiency and minimize variability of recoveries. In addition, care should be placed to verify the 

accuracy of all reference materials used in the method (i.e. DNA standards, calibrator cells, control 

DNA’s and spike materials). 

In Method 1611, water samples are filtered to collect enterococci on polycarbonate membrane filters. 

Following filtration, total DNA is solubilized from the filter retentate using a bead beater. Enterococci 

target DNA sequences present in the clarified homogenate are detected by the real time polymerase chain 

reaction (PCR) technique using TaqMan® Universal master mix PCR reagent and the TaqMan® probe 

system. The TaqMan® system signals the formation of PCR products by a process involving enzymatic 

hydrolysis of a fluorogenically-labeled oligonucleotide probe when it hybridizes to the target sequence. 

Method 1611 uses an arithmetic formula, referred to as the ΔΔCT comparative cycle threshold calculation 

(ΔΔCT) method to calculate the ratio of Enterococcus lsrRNA gene target sequences (target sequences) 
vi

recovered in total DNA extracts from water samples relative to those in similarly-prepared extracts of 

calibrator samples containing a known quantity of Enterococcus cells. The ΔΔCT relative quantitation 

method also uses measurements of a reference target sequence (from total salmon DNA, added in equal 

amounts to both test and calibrator samples) to normalize these ratios for potential differences in DNA 

recovery. The reference target sequence measurements are also used to signal inhibition or fluorescence 

quenching of the PCR analysis caused by sample matrix components or possible technical error. These 

ratios are converted to calibrator cell equivalents (CCEs) recovered from the test samples. 
vii

Table of Contents

1.0 Scope and Application ..................................................................................................................... 1 

2.0 Summary of Method ........................................................................................................................ 2 

3.0 Definitions ....................................................................................................................................... 2 

4.0 Interferences ..................................................................................................................................... 3 

5.0 Safety ............................................................................................................................................... 3 

6.0 Equipment and Supplies .................................................................................................................. 3 

7.0 Reagents and Standards ................................................................................................................... 5 

8.0 Sample Collection, Handling, and Storage ...................................................................................... 9 

9.0 Quality Control ................................................................................................................................ 9 

10.0 Calibration and Standardization of Method-Related Instruments .................................................. 14 

11.0 Procedure ....................................................................................................................................... 14 

12.0 Data Analysis and Calculations ..................................................................................................... 25 

13.0 Sample Spiking Procedure ............................................................................................................. 27 

14.0 Method Performance ...................................................................................................................... 33 

15.0 Pollution Prevention ...................................................................................................................... 34 

16.0 Waste Management ........................................................................................................................ 35 

17.0 References ...................................................................................................................................... 35 

18.0 Acronyms ....................................................................................................................................... 35 
viii

List of Appendices

Appendix A: ABI StepOnePlusTM, ABI 7900, and ABI 7500 Real-Time PCR System Operation 

Appendix B: Cepheid Smart Cycler® Operation 
1

Method 1611: Enterococci in Water by TaqMan® Quantitative 

Polymerase Chain Reaction (qPCR) Assay 

October 2012 

1.0 Scope and Application

1.1 Method 1611 describes a quantitative polymerase chain reaction (qPCR) procedure for the 

measurement of large subunit ribosomal RNA (lsrRNA, 23S rRNA) target gene sequences (target 

sequences) from all known species of enterococci bacteria in water. This method is based on the 

collection of enterococci on membrane filters, extraction of total DNA using a bead beater, and 

detection of enterococci target sequences in the supernatant by real time polymerase chain 

reaction (qPCR) using TaqMan® Universal master mix PCR reagent and the TaqMan® probe 

system. The TaqMan® system signals the formation of PCR products by a process involving the 

enzymatic hydrolysis of a labeled fluorogenic probe that hybridizes to the target sequence. 

1.2 The Method 1611 test is recommended as a measure of ambient marine and fresh recreational 

water quality. The significance of finding Enterococcus DNA target sequences in recreational 

water samples stems from the association between the density of these sequences and the reported 

occurrence of gastrointestinal (GI) illness associated with swimming observed in recent 

epidemiological studies (References 17.4 and 17.10). 

1.3 The highly variable recoveries observed during the validation studies should be taken into 

consideration when analyzing results from Method 1611. Guidance is provided in section 9 of 

this document on how laboratories can monitor the initial and ongoing performance of the method 

in their hands. It is expected and has been observed that the performance of the method will 

improve as laboratories gain additional experience with it through continued practice. 

1.4 This method assumes the use of an Applied Biosystems (ABI) Real-Time PCR System as the 

default platform. The Cepheid Smart Cycler® may also be used. The user should refer to the 

platform specific instructions for these instruments in the appendices. Users should thoroughly 

read the method in its entirety before preparation of reagents and commencement of the method 

to identify differences in protocols for different platforms. 
Method 1611 

2

2.0 Summary of Method

 The method is initiated by filtering a water sample through a membrane filter. Following 

filtration, the membrane containing the bacterial cells and DNA is placed in a microcentrifuge 

tube with glass beads and buffer, and then agitated to extract the DNA into solution. The 

supernatant is used for PCR amplification and detection of target sequences using the TaqMan®

Universal master mix PCR reagent and probe system. 

3.0 Definitions

3.1 Enterococci: all species of the genus Enterococcus for which lsrRNA gene nucleotide sequences 

were reported in the GenBank database (http://www.ncbi.nlm.nih/gov/Genbank) at the time of 

method development. 

3.2 Target sequence: A segment of the Enterococcus lsrRNA gene containing nucleotide sequences 

that are homologous to both the primers and probe used in the Enterococcus qPCR assay and that 

are common only to species within this genus. 

3.3 Sample processing control (SPC) sequence (may also be referred to as reference sequence): A 

segment of the ribosomal RNA gene operon, internal transcribed spacer region 2 of chum salmon,

Oncorhynchus keta (O. keta) and other salmon spp., containing nucleotide sequences that are 

homologous to the primers and probe used in the SPC qPCR assay. SPC sequences are added as 

part of a total salmon DNA solution in equal quantities to all water and calibrator sample filters 

prior to extracting DNA from the samples. The purpose of this control is to determine, and, if 

necessary, correct for different relative efficiencies of total DNA recovery from water and 

calibrator sample extracts using the ΔΔCT comparative cycle threshold calculation method (ΔΔCT

method) as described in Section 12.3. This control is also used to signal potential co-extraction of 

water sample components that interfere with the PCR analysis as described in Section 9.12. 

3.4 DNA standard: A purified, RNA-free and spectrophotometrically quantified and characterized E. 

faecalis strain ATCC® # 29212TM genomic DNA preparation. DNA standards are used to 

generate standard curves for determination of performance characteristics of the qPCR assays and 

instrument with different preparations of master mixes containing TaqMan® reagent, primers and 

probe as described in Section 9.10. Also used for quantifying target sequences in calibrator 

sample extracts as described in Section 12.3. 

3.5 Calibrator sample: Samples containing constant added quantities of E. faecalis strain ATCC® # 

29212TM cells and SPC sequences that are extracted and analyzed in the same manner as water 

sample filtrates. Calibrator sample analysis results are used as positive controls for the 

Enterococcus target sequence and SPC qPCR assays and as the basis for target sequence 

quantification in water sample filtrates using the ΔΔCT comparative cycle threshold calculation 

method (ΔΔCT method) as described in Section 12.3. Analysis results of these samples provide 

corrections for potential method-related variations in Enterococcus cell lysis, target sequence 

recovery and PCR efficiency. 

3.6 ΔΔCT method: A calculation method derived by ABI (Reference 17.1) for calculating the ratios of 

target sequences in two DNA samples (e.g., a calibrator and water filtrate sample) that normalizes 

for differences in total DNA recovery from these samples using qPCR analysis CT values for a 

reference (SPC) sequence that is initially present in equal quantities prior to DNA extraction. 
Method 1611 

3

3.7 Amplification factor (AF): A measure of the average efficiency at which target or SPC sequences 

are copied and detected by their respective primer and probe assays during each thermal cycle of 

the qPCR reaction that is used in the ΔΔCT method. AF values can range from 1 (0% of 

sequences copied and detected) to 2 (100% of sequences copied and detected) and are calculated 

from a standard curve as described in Section 12.2. For an explanation of test inhibition, see 

Section 9.12. 

4.0 Interferences

Water samples containing colloidal or suspended particulate materials can clog the membrane 

filter and prevent filtration. These materials can also interfere with DNA recovery and with the 

qPCR analysis by inhibiting the enzymatic activity of the Taq DNA polymerase, and/or inhibiting 

the annealing of the primer and probe oligonucleotides to sample target DNA, enzyme or 

quenching of hydrolyzed probe fluorescence. 

 

5.0 Safety

5.1 The analyst / technician must know and observe the normal safety procedures required in a 

microbiology and/or molecular biology laboratory while preparing, using, and disposing of 

cultures, reagents, and materials, and while operating sterilization equipment. 

5.2 Where possible, facial masks should be worn to prevent sample contamination. 

5.3 Mouth-pipetting is prohibited. 

6.0 Equipment and Supplies

6.1 Separated, and dedicated workstations for reagent preparation and for sample preparation, 

preferably with HEPA-filtered laminar flow hoods and an Ultraviolet (UV) light source, each 

having separate supplies (e.g., pipettors, tips, gloves, etc.). Note: The same workstation may be 

used for the entire procedure provided that it has been cleaned with bleach and UV sterilized as 

specified in Section 11.6.1 between reagent and sample preparation. Under ideal conditions, two 

dedicated workstations are used for sample preparation: one for preparing samples with high 

target sequence DNA concentrations (e.g., DNA standards and calibrator samples) and one for 

preparing samples with expected low target sequence DNA concentrations (e.g., filter blanks and 

ambient water samples). 

6.2 Balance capable of accuracy to 0.01 g 

6.3 Extraction tubes: semi-conical, screw cap microcentrifuge tubes, 2.0 mL (PGC 506-636 or 

equivalent) 

6.4 Glass beads, acid washed, 212 − 300 μm diameter (Sigma G-1277 or equivalent) 

6.5 Autoclave, capable of achieving and maintaining 121C [15 lb pressure per square inch (PSI)] for 

minimally 15 minutes (optional) 

6.6 Workstation for water filtrations, preferably a HEPA-filtered laminar flow hood with a UV light 

source. This can be the same as used for sample preparation (Section 6.1). 
Method 1611 

4

6.7 Sterile bottles/containers for sample collection 

6.8 Membrane filtration units (filter base and funnel) for 47 mm diameter filters, sterile glass, plastic 

(Pall Gelman 4242 or equivalent), stainless steel, or disposable plastic (Nalgene CN 130-4045 or 

CN 145-0045 or equivalent), cleaned and bleach treated (rinsed with 10% v/v bleach, then 3 

rinses with reagent-grade water), covered with aluminum foil or Kraft paper, and autoclaved or 

UV-sterilized if non-disposable. 

6.9 Line vacuum, electric vacuum pump, or aspirator for use as a vacuum source. In an emergency or 

in the field, a hand pump or a syringe equipped with a check valve to prevent the return flow of 

air can be used. 

6.10 Flask, filter, vacuum, usually 1 L, with appropriate tubing 

6.11 Filter manifold to hold a number of filter bases 

6.12 Flask for safety trap placed between the filter flask and the vacuum source 

6.13 Forceps, straight or curved, with smooth tips to handle filters without damage, 2 pairs 

6.14 Polycarbonate membrane filters, sterile, white, 47 mm diameter, with 0.45 μm pore size 

(GE Osmonics Inc. K04CP04700 or equivalent) 

6.15 Graduated cylinders, 100 - 1000 mL, cleaned and bleach treated (rinsed with 10% v/v bleach, 

then 3 rinses with reagent-grade water), covered with aluminum foil or Kraft paper and 

autoclaved or UV-sterilized. 

6.16 Petri dishes, sterile, plastic or glass, 100 × 15 mm with loose fitting lids 

6.17 Disposable loops, 1 and 10 μL 

6.18 Permanent ink marking pen for labeling tubes 

6.19 Visible wavelength spectrophotometer capable of measuring at 595 nm 

6.20 Single or multi-place bead beater (Biospec Products Inc. 3110BX or equivalent) 

6.21 Microcentrifuge capable of 12,000 × g 

6.22 Micropipettors with 10, 20, 200 and 1000 μL capacity. Under ideal conditions, each workstation 

should have a dedicated set of micropipettors (one micropipettor set for pipetting reagents not 

containing cells or reference DNA and one set for reagents containing reference DNA and for test 

samples). Ideally, micropipettors should be calibrated monthly. 

6.23 Micropipettor tips with aerosol barrier for 10, 20, 200 and 1000 μL capacity micropipettors. 

Note: All micropipetting should be done with aerosol barrier tips. The tips used for reagents not 

containing DNA should be separate from those used for reagents containing DNA and test 

samples. Each workstation should have a dedicated supply of tips. 

6.24 Microcentrifuge tubes, low retention, clear, 1.7 mL (GENE MATE C-3228-1 or equivalent) 

6.25 Test tube rack for microcentrifuge tubes, use a separate rack for each set of tubes 

6.26 Conical centrifuge tubes, sterile, screw cap, 50 mL 

6.27 Test tubes, screw cap, borosilicate glass, 16 × 125 mm 

6.28 Pipet containers, stainless steel, aluminum or borosilicate glass, for glass pipets 

6.29 Pipets, sterile, T.D. bacteriological or Mohr, disposable glass or plastic, of appropriate volume 

(disposable pipets preferable) 

6.30 Vortex mixer (ideally one for each work station) 
Method 1611 

5

6.31 Dedicated lab coats for each work station 

6.32 Disposable powder-free gloves for each work station 

6.33 Refrigerator, 4C (ideally one for reagents and one for DNA samples) 

6.34 Freezer, -20C or -80C (ideally one for reagents and one for DNA samples) 

6.35 Ice, crushed or cubes for temporary preservation of samples and reagents 

6.36 Printer (optional) 

6.37 Data archiving system (e.g., flash drive or other data storage system) 

6.38 UV spectrophotometer capable of measuring wavelengths of 260 and 280 nm using small volume 

capacity (e.g., 0.1 mL) cuvettes or NanoDrop® (ND-2000 spectrophotometer or equivalent) 

capable of the same measurements at 2 μL sample volumes 

6.39 ABI StepOnePlusTM, ABI 7900, or ABI 7500 

6.39.1 Optical 96 well PCR reaction tray (ABI N801-0560 or equivalent) 

6.39.2 Optical adhesive PCR reaction tray tape (ABI 4311971 or equivalent) or MicroAmpTM 

caps (ABI N8010534 or equivalent) 

6.39.3 ABI StepOnePlusTM, ABI 7900, or ABI 7500 Real-Time PCR System 

6.40 Cepheid (optional to ABI) 

6.40.1 Smart Cycler® 25 μL PCR reaction tubes (Cepheid 900-0085 or equivalent) 

6.40.2 Rack and microcentrifuge for Smart Cycler® PCR reaction tubes. Note: Racks and 

microcentrifuge are provided with the Smart Cycler® thermocycler 

6.40.3 Cepheid Smart Cycler® System Thermocycler 

7.0 Reagents and Standards 

Note: The E. faecalis stock culture (Section 7.8), Salmon DNA/extraction buffer (Section 7.12), 

and DNA extraction tubes (Section 7.18), may be prepared in advance. 

7.1 Purity of Reagents: Molecular-grade reagents and chemicals shall be used in all tests 

7.2 Control Culture 

• Enterococcus faecalis (E. faecalis) ATCC® #29212TM (ATCC, Manassas VA) or 

• E. faecalis ATCC® # 29212TM (550 colony forming units [CFU]) BioBalls (bioMérieux Inc., 

Durham NC) 

7.3 Sample Processing Control (SPC) DNA 

• Salmon testes DNA (Sigma D1626 or equivalent) 
Method 1611 

6

7.4 Phosphate Buffered Saline (PBS) 

7.4.1 Composition: 

Monosodium phosphate (NaH2PO4) 0.58 g 

Disodium phosphate (Na2HPO4) 2.50 g 

Sodium chloride 8.50 g 

Reagent-grade water 1.0 L 

7.4.2 Dissolve reagents in 1 L of reagent-grade water in a flask and dispense in appropriate 

amounts for dilutions in screw cap bottles or culture tubes, and/or into containers for use 

as rinse water. Autoclave after preparation at 121C (15 lb PSI) for 15 minutes. Final 

pH should be 7.4 ± 0.2. 

7.5 Brain heart infusion broth (BHIB) 

7.5.1 Composition: 

Calf brains, infusion from 200.0 g 7.7 g 

Beef heart, infusion from 250.0 g 9.8 g 

Proteose peptone 10.0 g 

Sodium chloride 5.0 g 

Disodium phosphate (Na2HPO4) 2.5 g 

Dextrose 2.0 g 

Reagent-grade water 1.0 L 

7.5.2 Add reagents to 1 L of reagent-grade water, mix thoroughly, and heat to dissolve 

completely. Dispense 10 mL volumes in screw cap 16 × 125 mm tubes and autoclave at 

121C (15 PSI) for 15 minutes. Final pH should be 7.4 ± 0.2. 

7.6 Brain heart infusion agar (BHIA) 

7.6.1 Composition: 

BHI agar contains the same components as BHIB with the addition of 15.0 g agar per 

liter of BHI broth. 

7.6.2 Add agar to formula for BHIB provided above. Prepare as in Section 7.5.2. After 

sterilization, dispense 12 − 15 mL into 100 × 15 mm petri dishes. Final pH should be 7.4 

± 0.2. 

7.7 Sterile glycerol (used for preparation of E. faecalis stock culture as described in Section 7.8) 

7.8 Preparation of E. faecalis (ATCC® # 29212TM) stock culture 

Rehydrate lyophilized E. faecalis per manufacturer’s instructions (for ATCC® stocks, suspend in 

5 - 6 mL of sterile BHIB and incubate at 37C for 24 hours). Centrifuge to create pellet. Using a 

sterile pipet, discard supernatant. Resuspend pellet in 10 mL of fresh sterile BHIB containing 

15% glycerol and dispense in 1.5 mL aliquots in microcentrifuge tubes. Freeze at -20C (short 

term storage) or -80C (long term storage). Note: Aliquots of suspension should be plated to 

determine CFU concentration as described in Section 11.1. It is also advisable to verify the E. 

faecalis culture as described, for example, in Section 15 of EPA Method 1600. 
Method 1611 

7

7.9 PCR-grade water (OmniPur water from VWR EM-9610 or equivalent). Water must be 

DNA/DNase free. 

7.10 Isopropanol or ethanol, 95%, for flame-sterilization 

7.11 AE Buffer, pH 9.0 (Qiagen 19077 or equivalent) Note: pH 8.0 is acceptable 

 Composition: 

 10 mM Tris-Cl (Tris-chloride) 

 0.5 mM EDTA (Ethylenediaminetetraacetic acid) 

7.12 Salmon DNA/extraction buffer 

7.12.1 Composition: 

Stock Salmon testes DNA (10 μg/mL) (Section 7.3) 

AE Buffer (Section 7.11) 

7.12.2 Preparation of stock Salmon testes DNA: Using sterilized scissors and sterilized forceps, 

cut a piece of DNA to weigh approximately 20 mg, and place in a sterile 50 mL conical 

tube. After weighing, add 20 mL of PCR-grade water. Cap tightly, and resuspend by 2 −

4 hours of vigorous shaking (note: longer times may be required to fully suspend the 

DNA – check for even consistency by repeatedly drawing up the suspension and 

expelling with a sterile 25 ml pipet) . The concentration should be about 1 mg/mL. 

Dilute a 1ml aliquot of this 1 mg/mL stock with 99 ml PCR-grade water to make 10 

μg/mL working stock. Check absorbance (OD260) and calculate DNA concentration 

using the assumption 50 μg/mL DNA is equal to 1 OD260, (i.e. 10 μg/mL should equal ~ 

0.2 OD260.). If measured concentration is different than 10 μg/mL, adjust dilutions to 

make 0.2 μg/mL Salmon DNA/extraction buffer in 7.12.3 accordingly. Dispense 1 

mg/mL stock and 10 μg/mL working stock suspensions into aliquots (e.g. 1 ml) and 

freeze at -20C. Frozen aliquots of working stock should be thawed only once, but once 

thawed can be stored in a refrigerator for several months. 

7.12.3 Dilute Salmon testes DNA working stock with AE buffer to make 0.2 μg/mL Salmon 

DNA/extraction buffer. Extraction buffer may be prepared in advance and stored at 4C 

for a maximum of 1 week. 

Note: Determine the total volume of Salmon DNA/extraction buffer required for each day 

or week by multiplying volume (600 μL) × total number of samples to be analyzed 

including controls, water samples, and calibrator samples. For example, for 18 samples, 

prepare enough Salmon/DNA extraction buffer for 24 extraction tubes: 3 tubes for water 

sample filtration blank (method blank) and 3 tubes for calibrator samples). Note: At least 

one method blank should be included with each sample batch. Additionally, prepare 

excess volume to allow for accurate dispensing of 600 μL per tube, generally enough for 

1 extra tube. Thus, in this example, prepare sufficient Salmon/DNA extraction buffer for 

24 tubes plus one extra. The total volume needed is 600 μL × 25 tubes = 15,000 μL. 

Dilute the Salmon testes DNA working stock 1:50, for a total volume needed (15,000 μL) 

÷ 50 = 300 μL of 10 μg/mL Salmon testes DNA working stock. The AE buffer needed is 

the difference between the total volume and the Salmon testes DNA working stock. For 

this example, 15,000 μL − 300 μL = 14,700 μL AE buffer needed. 

7.13 Bleach solution: 10% v/v bleach (or other reagent that hydrolyzes DNA), used for cleaning work 

surfaces 

7.14 Sterile water (used as rinse water for work surface after bleaching) 
Method 1611 

8

7.15 TaqMan® Universal PCR master mix (ABI 4304437 or equivalent) 

 Composition: 

 AmpliTaq Gold® DNA Polymerase 

 AmpErase® UNG 

 dNTPs with dUTP 

 Passive Reference 1 (ROXTM fluorescent dye) 

 Optimized buffer components (KCl, Tris, EDTA, MgCl2) 

7.16 Bovine serum albumin (BSA), fraction V powder (Sigma B-4287 or equivalent) 

Dissolve in PCR-grade water to a concentration of 2 mg/mL. 

7.17 Primer and probe sets: Primer and probe sets may be purchased from commercial sources. 

Primers should be desalted, probes should be HPLC purified. 

7.17.1 Enterococcus primer and probe set (Reference 17.5): 

Forward primer: 5'-GAGAAATTCCAAACGAACTTG 

Reverse primer: 5'-CAGTGCTCTACCTCCATCATT 

TaqMan® probe: [6-FAM]-5'-TGGTTCTCTCCGAAATAGCTTTAGGGCTA-TAMRA 

7.17.2 Salmon DNA primer and probe set (Reference 17.4): 

Forward primer: 5'-GGTTTCCGCAGCTGGG 

Reverse primer (Sketa 22): 5'-CCGAGCCGTCCTGGTC 

TaqMan® probe: [6-FAM]-5'-AGTCGCAGGCGGCCACCGT-TAMRA 

7.17.3 Preparation of primer/probes: Using a micropipettor with aerosol barrier tips, add PCR 

grade water to the lyophilized primers and probe from the vendor to create stock 

solutions of 500 μM primer and 100 μM probe and dissolve by extensive vortexing. 

Pulse centrifuge to coalesce droplets. Store stock solutions at -20C. 

7.18 DNA extraction tubes 

 Note: It is recommended that tube preparation be performed in advance of water sampling and 

DNA extraction procedures. 

Prepare 1 tube for each sample, and 1 extra tube for every 6 samples (i.e., for method blank) and 

a minimum of 3 tubes per week for calibrator samples. Weigh 0.3 ± 0.01 g of glass beads 

(Section 6.4) and pour into extraction tube. Seal the tube tightly, checking to make sure there are 

no beads on the O-ring of the tube. Check the tube for proper O-ring seating after the tube has 

been closed. Autoclave tubes at 121C (15 PSI) for 15 minutes. Note: Sterile extraction tubes 

containing glass beads are available from Generite LLC., (50205-50 or equivalent). 

7.19 Purified, RNA-free quantified and characterized E. faecalis genomic DNA preparations for use as 

standards used to generate a standard curve (see Section 11.2 for preparation instructions). 

7.20 RNase A 5 mg/mL (epicentre® MRNA092 or equivalent) 

7.21 DNA extraction kit (Gene-Rite K102-02C-50 DNA-EZ® RW02 or equivalent) 

 
Method 1611 

9

8.0 Sample Collection, Handling, and Storage 

8.1 Sampling procedures are briefly described below. Adherence to sample preservation procedures 

and holding time limits is critical to the production of valid data. Samples not collected 

according to these procedures should not be analyzed. Note: It is recommended that when 

possible that three samples be collected and analyzed from each sample location. 

8.2 Sampling Techniques 

Samples are collected by hand or with a sampling device if the sampling site has difficult access 

such as a dock, bridge or bank adjacent to a surface water. Composite samples should not be 

collected, since such samples do not display the range of values found in individual samples. The 

sampling depth for surface water samples should be 6 − 12 inches below the water surface. 

Sample containers should be positioned such that the mouth of the container is pointed away from 

the sampler or sample point. After removal of the container from the water, a small portion of the 

sample should be discarded to provide head space for proper mixing before analyses. 

8.3 Storage Temperature and Handling Conditions 

Ice or refrigerate water samples at a temperature of <10C during transit to the laboratory. Do 

not freeze the samples. Use insulated containers to assure proper maintenance of storage 

temperature. Ensure that sample bottles are tightly closed and are not completely immersed in 

water during transit. 

8.4 Holding Time Limitations 

Examine samples as soon as possible after collection. Do not hold samples longer than 6 hours 

between collection and initiation of filtration. 

9.0 Quality Control 

9.1 Each laboratory that uses Method 1611 is required to operate a formal quality assurance (QA) 

program that addresses and documents instrument and equipment maintenance and performance, 

reagent quality and performance, analyst training and certification, and records storage and 

retrieval. Additional recommendations for QA and quality control (QC) procedures for 

microbiological laboratories are provided in Reference 17.2. 

9.2 The minimum analytical QC requirements for the analysis of samples using Method 1611 include 

an initial demonstration of laboratory capability through performance of the initial precision and 

recovery (IPR) analyses (Section 9.3), ongoing demonstration of laboratory capability through 

performance of the ongoing precision and recovery (OPR) analysis (Section 9.4) and matrix spike 

(MS) analysis (Section 9.5), and the routine analysis of positive control (Section 9.6), no template 

controls (Section 9.7), method blanks (Section 9.8), media sterility checks (Section 9.9), DNA 

standard curves (9.10), calibrator samples (9.11), and sample processing controls (9.12). For the 

IPR, OPR and MS analyses, it is necessary to spike samples with either laboratory-prepared 

spiking suspensions or BioBalls as described in Section 13. 

9.3 Initial precision and recovery (IPR) — The IPR analyses are used to demonstrate acceptable 

method performance (recovery and precision) and should be performed by each laboratory before 

the method is used for monitoring field samples. An IPR should be performed by each analyst. 

The IPR analyses are performed as follows: 

9.3.1 Prepare four, 100 mL samples of PBS and spike each sample with the control culture, E. 

faecalis ATCC® # 29212TM according to the spiking procedure in Section 13. Spiking 
Method 1611 

10

with laboratory-prepared suspensions is described in Section 13.4 and spiking with a 

commercially prepared product (e.g., BioBalls) is described in Section 13.7. Filter and 

process each IPR sample according to the procedures in Section 11 and calculate the 

calibrator cell equivalents (CCEs) in the samples according to Section 12. Note: prepare 

calibrator samples from the same source of cells used to prepare the spike suspensions, 

i.e. for samples spiked with laboratory-prepared cell suspensions, use the same 

laboratory-prepared cell suspensions to prepare calibrator samples; for samples spiked 

with BioBalls, use the same lot of BioBalls to prepare calibrator samples. 

9.3.2 Calculate the percent recovery (R) for each IPR sample according to the Method 1611 

Calculation Excel file using the appropriate spreadsheets “Laboratory-prepared” or 

“BioBalls” for samples spiked with laboratory-prepared spiking suspensions or BioBalls, 

respectively. 

9.3.3 Using the percent recoveries of the four analyses, calculate the mean percent recovery 

and the relative standard deviation (RSD) of the recoveries. The RSD is the standard 

deviation divided by the mean, multiplied by 100. 

9.3.4 Compare the mean recovery and RSD with the corresponding IPR criteria in Table 1, 

below. If the mean and RSD for recovery of enterococci meet acceptance criteria, system 

performance is acceptable and analysis of field samples may begin. If the mean recovery 

or the RSD fall outside of the required range for recovery, system performance is 

unacceptable. In this event, identify the problem by evaluating each step of the analytical 

process, media, reagents, and controls, correct the problem and repeat the IPR analyses. 

Table 1. Calculated Initial Precision and Recovery (IPR) Acceptance Criteria at 

550 CFU 

Spike Type IPR Mean Recovery (%) IPR RSD OPR Recovery (%) 

Lab-prepared Detect – 2684% 132 Detect – 2846% 

BioBall® Detect – 286% 112 Detect – 325% 

9.4 Ongoing precision and recovery (OPR) — To demonstrate ongoing control of the analytical 

system, the laboratory should routinely process and analyze spiked PBS samples. The laboratory 

should analyze one OPR sample after every 20 field and matrix spike samples or one per week 

that samples are analyzed, whichever occurs more frequently. The OPR analysis is performed as 

follows: 

9.4.1 Prepare one, 100 mL sample of PBS and spike with E. faecalis ATCC® # 29212TM 

according to the spiking procedure in Section 13. Spiking with laboratory-prepared 

suspensions is described in Section 13.4 and spiking with BioBalls is described in Section 

13.7. Filter and process the OPR sample according to the procedures in Section 11 and 

calculate the target sequences in the samples according to Section 12. 

9.4.2 Calculate the percent recovery (R) for the OPR sample according to the Method 1611 

Calculation Excel file using the appropriate spreadsheets “Laboratory-prepared” or 

“BioBalls” for samples spiked with laboratory-prepared spiking suspensions or BioBalls, 

respectively. 

9.4.3 Compare the OPR result (percent recovery) with the corresponding OPR recovery criteria 

in Table 1, above. If the OPR result meets the acceptance criteria for recovery, method 

performance is acceptable and analysis of field samples may continue. If the OPR result 

falls outside of the acceptance criteria, system performance is unacceptable. In this 
Method 1611 

11

event, identify the problem by evaluating each step of the analytical process, reagents, 

and controls, correct the problem and repeat the OPR analysis. 

9.4.4 As part of the laboratory QA program, results for OPR and IPR samples should be 

charted and updated records maintained in order to monitor ongoing method 

performance. The laboratory should also develop a statement of accuracy for Method 

1611 by calculating the average percent recovery (R) and the standard deviation of the 

percent recovery (sr). Express the accuracy as a recovery interval from R - 2sr to R + 2sr. 

9.5 Matrix spikes (MS) — MS analysis are performed to determine the effect of a particular matrix 

on enterococci recoveries. The laboratory should analyze one MS sample when recreational 

water samples are first received from a source from which the laboratory has not previously 

analyzed samples. Subsequently, 5% of field samples (1 per 20) from a given source should 

include a MS sample. MS samples must be accompanied by the analysis of an unspiked field 

sample sequentially collected from the same sampling site. When possible, MS analyses should 

also be accompanied by an OPR sample (Section 9.4), using the same spiking procedure 

(laboratory-prepared spiking suspension or BioBalls). The MS analysis is performed as follows: 

9.5.1 Prepare two, 100 mL field samples that were sequentially collected from the same site. 

One sample will remain unspiked and will be analyzed to determine the background or 

ambient concentration of enterococci for calculating MS recoveries (Section 9.5.3). The 

other sample will serve as the MS sample and will be spiked with E. faecalis ATCC® # 

29212TM according to the spiking procedure in Section 13. 

9.5.2 Spike the MS sample volume(s) with a laboratory-prepared suspension as described in 

Section 13.4 or with BioBalls as described in Section 13.7. Immediately filter and 

analyze both the unspiked and spiked field samples according to the procedures in 

Section 11. 

9.5.3 For the MS sample, calculate the number of target sequences according to Section 12 and 

adjust based on any background enterococci observed in the unspiked matrix sample. 

9.5.4 Calculate the percent recovery (R) for the MS sample (adjusted based on ambient 

enterococci in the unspiked sample) according to the Method 1611 Calculation Excel file 

using the appropriate spreadsheets “Laboratory-prepared” or “BioBalls” for samples 

spiked with laboratory-prepared spiking suspensions or BioBalls, respectively. 

9.5.5 Compare the MS result (percent recovery) with the appropriate method performance 

criteria in Table 2, below. If the MS recovery meets the acceptance criteria, system 

performance is acceptable and analysis of field samples from this disinfected wastewater 

source may continue. If the MS recovery is unacceptable and the OPR sample result 

associated with this batch of samples is acceptable, a matrix interference may be causing 

the poor results. If the MS recovery is unacceptable, all associated field data should be 

flagged. 

9.5.6 Laboratories should record and maintain a control chart comparing MS recoveries for all 

matrices to batch-specific and cumulative OPR sample results analyzed using Method 

1611. These comparisons should help laboratories recognize matrix effects on method 

recovery and may also help to recognize inconsistent or sporadic matrix effects from a 

particular source. 
Method 1611 

12

Table 2. Calculated Matrix Spike Precision and Recovery Acceptance Criteria at 

550 CFU 

Matrix Spike Type MS Recovery (%) MS RPD 1 (%) 

MW Lab-prepared Detect – 1198% 160 

BioBall® Detect – 1123% 191 

FW Lab-prepared Detect – 3473% 110 

BioBall® Detect – 333% 354 1

 Relative percent difference 

9.6 Positive controls — The laboratory should analyze positive controls to ensure that the method is 

performing properly. Fluorescence amplification growth curve (PCR amplification trace) with an 

appropriate cycle threshold (CT) value during PCR indicates proper method performance. On an 

ongoing basis, the laboratory should perform positive control analyses every day that samples are 

analyzed. In addition, controls should be analyzed when new lots of reagents or filters are used. 

9.6.1 Calibrator samples will serve as the positive control. Analyze as described in Section 

11.0. Note: Calibrator samples contain the same amount of extraction buffer and starting 

amount of Salmon DNA as the test samples; hence E. faecalis calibrator sample extracts 

(Section 11.3) will be used as a positive control for both Enterococcus and SPC qPCR 

assays. 

9.6.2 If the positive control fails to exhibit the appropriate fluorescence growth curve response, 

check and/or replace the associated reagents, and reanalyze. If positive controls still fail 

to exhibit the appropriate fluorescence growth curve response, prepare new calibrator 

samples and reanalyze (see Section 9.11). 

9.7 No template controls — The laboratory should analyze “No Template Controls” (NTCs) to 

ensure that the PCR master mix reagents are not contaminated. On an ongoing basis, the 

laboratory should perform NTC analyses every day that samples are analyzed. If greater than 

one-third of the NTC reactions for a PCR master mix exhibit true positive logarithmic 

amplification traces with CT values below 45 (not from chemical degradation of probe with linear 

kinetics that exhibit rising baseline) or if any one NTC reaction has a CT value lower than 35, the 

analyses should be repeated with new master mix working stock preparations. 

9.8 Method blank (water sample filtration blank) — Filter a 50 mL volume of sterile PBS before 

beginning the sample filtrations. Remove the funnel from the filtration unit. Using two sterile or 

flame-sterilized forceps, fold the filter on the base of the filtration unit and place it in an 

extraction tube with glass beads as described in Section 7.18. Extract as in Section 11.5. The 

absence of a fluorescence amplification growth curve during PCR analysis of these samples 

(reported as “0” on Smart Cycler® and “undetermined” on ABI instruments) indicates the absence 

of contaminant target DNA (see Data Quality Acceptance, below). Prepare at least one method 

blank filter for every PCR run (e.g., minimally one method blank per 96 well plate or Smart 

Cycler run).

9.9 Media sterility check — The laboratory should test media sterility by incubating one 

uninoculated unit (tube or plate) from each batch of medium (BHIA/BHIB) as appropriate and 

observing for growth. Absence of growth indicates media sterility. On an ongoing basis, the 

laboratory should perform media sterility checks when preparing new E. faecalis cell stocks. 

9.10 DNA standards and standard curves –Purified, RNA-free and spectrophotometrically 

quantified E. faecalis genomic DNA should be prepared as described in Section 11.2. Based on 

reported values for its size, the weight of a single E. faecalis genome can be estimated to be ~3.6 

fg and there are four lsrRNA gene copies per genome in this species (see the rRNA operon 
Method 1611 

13

database at http://rrndb.cme.msu.edu). The concentration of lsrRNA gene copies per μL in the 

standard E. faecalis genomic DNA preparation can be determined from this information and from 

its spectrophotometrically determined total DNA concentration by the formula: 

Concentration of lsrRNA 

gene copies per μL = 

Total DNA concentration (fg/μL) 

× 

4 lsrRNA gene copies 

3.6 fg/genome genome 

A composite standard curve should be generated from multiple analyses of serial dilutions of this 

DNA standard using the Enterococcus primer and probe assay and subjected to linear regression 

analysis as described in Section 12.2. From that point on, it is recommended that additional 

standard curves be generated from triplicate analyses of these same diluted standard samples with 

each new lot of TaqMan® master mix reagents or primers and probes to demonstrate comparable 

performance by these new reagents. The r2

 values from regressions of these curves should ideally 

be 0.99 or greater. Comparable performance is assessed by their slopes and y-intercepts which 

should be consistent with those from the initial composite analyses (e.g., within the 95% 

confidence range of the average values). Note: The 95% confidence ranges for these parameters 

in the initial composite standard curve can be generated using the Regression Analysis Tool 

which can be accessed from the “Data Analysis” selection under the “Tools” menu in Excel. 

Subsequent regressions can be performed by plotting the data using the Chart Wizard in Excel 

and using the “add trend line” selection in the Chart menu and “display equation on chart” 

selection under Options to obtain slope and y-intercept values as illustrated in Section 12.2. 

In the event that the slope value from a subsequent standard curve regression is outside of the 

acceptance range, the diluted standards should be re-analyzed. If this difference persists, new 

working stocks of the reagents should be prepared and the same procedure repeated. If the 

differences still persist, the amplification factor values used for calculations of target cell 

numbers, as described in Section 12, should be modified based on the new slope values. If the 

slopes are within acceptance range but y-intercepts are not within acceptance range of this 

previous average, new aliquots of serial dilutions of the DNA standard should be analyzed or 

prepared and analyzed as described in Section 11.2 and above. 

9.11 Calibrator samples — The cell concentration of each cultured E. faecalis stock suspension used 

for the preparation of calibrator sample extracts should be determined as described in Section 

11.1. A minimum of nine calibrator sample extracts should initially be prepared from three 

different freezer-stored aliquots of these stocks as described in Section 11.3. Dilutions of each of 

these calibrator sample extracts equivalent to the anticipated dilutions of the test samples used for 

analysis (e.g., 1-, 5- and/or 25-fold) should be analyzed with the Enterococcus primer and probe 

assay. The average and standard deviation of the CT values from these composite analyses should 

be determined. From that point on, a minimum of three fresh calibrator sample extracts should be 

prepared from an additional frozen aliquot of the same stock cell suspension at least weekly and 

preferably daily before analyses of each batch of test samples. Dilutions of each new calibrator 

sample extract equivalent to the initial composite dilutions (e.g., 1-, 5- and/or 25-fold) should be 

analyzed using the Enterococcus primer and probe assay. The average CT value from these 

analyses should not be significantly different from the laboratory’s average values from analyses 

of the initial calibrator sample extracts from the same stock cell suspension (i.e., not greater than 

three standard deviations). If these results are not within this acceptance range, new calibrator 

extracts should be prepared from another frozen aliquot of the same stock cell suspension and 

analyzed in the same manner as described above. If the results are still not within the acceptance 

range, the reagents should be checked by the generation of a standard curve as described in 

Section 9.10. 
Method 1611 

14

9.12 Salmon DNA SPC sequence analyses — The Salmon DNA SPC is used as a DNA isolation 

efficiency control. While not essential, it is good practice to routinely prepare and analyze 

standard curves from serial dilutions of Salmon DNA working stocks in a manner similar to that 

described for the Enterococcus DNA standards in Section 9.10. At this time rRNA gene operon 

copy numbers per genome have not been reported in the literature for the salmon species O. keta. 

Therefore log-transformed total DNA concentration values or dilution factor values can be 

substituted for target sequence copy numbers as the x-axis values in these plots and regression 

analyses. 

In general, target DNA concentrations in test samples can be calculated as described in Section 

12. However, the Salmon DNA PCR assay results for each test sample’s 5-fold dilution should 

be within 3 CT units of the mean of the 5-fold diluted calibrator (and/or method blank) Salmon 

DNA sample results. Higher CT values may indicate significant PCR inhibition or poor DNA 

recovery possibly due to physical, chemical, or enzymatic degradation. Repeat the Enterococcus

and Salmon DNA PCR assays of any samples whose 5-fold dilution exhibits a Salmon DNA PCR 

assay CT value greater than 3 CT units higher than the mean of the calibrator sample results using 

a 5-fold higher dilution (net dilution: 25-fold) of the extracts. The Enterococcus PCR result from 

assaying the original 5-fold dilution of the sample can be accepted if its Salmon DNA assay CT

value is lower than that of the corresponding 25-fold dilution of the sample. This pattern of 

results is indicative of poor recovery of total DNA in the extract rather than PCR inhibition. The 

poor DNA recovery is compensated for by the calculation method. Contrarily, if the Salmon 

PCR assay CT value of the 25-fold dilution of the sample is lower than that of the 5-fold dilution 

of the sample, then the Enterococcus PCR assay result from the 25-fold dilution of the sample is 

considered more accurate. However the Enterococcus PCR results should be reported as 

questionable if the Salmon DNA assay’s result is still not within 3 CT units of the mean CT result 

of the 25-fold dilution of the three calibrators. 

10.0 Calibration and Standardization of Method-Related Instruments 

10.1 Check temperatures in incubators twice daily with a minimum of 4 hours between each reading to 

ensure operation within stated limits. 

10.2 Check thermometers at least annually against a NIST certified thermometer or one that meets the 

requirements of NIST Monograph SP 250 -23. Check columns for breaks. 

10.3 The spectrophotometer should be calibrated each day of use using OD calibration standards 

between 0.01 − 0.5. Follow manufacturer instructions for calibration. 

10.4 Micropipettors should be calibrated at a minimum annually, ideally monthly, and tested for 

accuracy on a weekly basis. Follow manufacturer instructions for calibration. 

10.5 Follow manufacturer instructions for calibration of real-time PCR instruments. 

11.0 Procedure 

Note: E. faecalis cell suspensions (Section 11.1) and E. faecalis DNA standards (Section 11.2) 

may be prepared in advance. Calibrator samples (Section 11.3) should be prepared at least 

weekly. 
Method 1611 

15

11.1 Preparation of E. faecalis cell suspensions for DNA standards and calibrator samples 

11.1.1 Thaw an E. faecalis (ATCC® # 29212TM) stock culture (Section 7.8) and streak for 

isolation on BHIA plates. Incubate plates at 37C ± 0.5C for 24 ± 2 hours. 

11.1.2 Pick an isolated colony of E. faecalis from BHIA plates and suspend in 1 mL of sterile 

PBS and vortex. 

11.1.3 Use 10 μL of the 1 mL suspension of E. faecalis to inoculate a 10 mL BHIB tube. Place 

the inoculated tube and one uninoculated tube (sterility check) on a shaker set at 250 rpm 

and incubate at 37C ± 0.5C for 24 ± 2 hours. Note: It is advisable to verify that the 

selected colony is Enterococcus as described, for example, in Section 15 of EPA Method 

1600. 

11.1.4 After incubation, centrifuge the BHIB containing E. faecalis for 5 minutes at 6000 × g. 

11.1.5 Aspirate the supernatant and resuspend the cell pellet in 10 mL PBS. 

11.1.6 Repeat the two previous steps twice and suspend the final E. faecalis pellet in 5 mL of 

sterile PBS. Label the tube as E. faecalis undiluted stock cell suspension, noting cell 

concentration after determination with one of the following steps (11.1.7). 

11.1.7 Determine calibrator sample cell concentrations based on one of two the options 

indicated below. 

• Option 1: Spectrophotometric absorbance – Remove three 0.1 mL aliquots of 

undiluted cell suspension and dilute each with 0.9 mL of PBS (10-1 dilution). Read 

absorbance at 595 nm in spectrophotometer against PBS blank (readings should 

range from 0.05 to 0.3 OD). Calculate cells/mL (Y) in undiluted cell suspension 

using the formula from the standard curve shown below where X is the average 595 

nm spectrophotometer reading. Note: Cell concentration (spectrophotometric 

determination) of undiluted E. faecalis cell suspension should be at least ~109

CFU/mL in order to obtain adequate DNA yield for accurate UV spectrophotometric 

reading. 

 Y = (1 × 109

 cells / mL × X) / 0.19 

• Option 2: plating – Note: PBS and BHIA plates should be prepared in advance if this 

option is chosen. For enumeration of the E. faecalis undiluted cell suspension, dilute 

and inoculate according to the following. 

A) Mix the E. faecalis undiluted cell suspension by vigorously shaking the 5 mL 

tube a minimum of 25 times. Use a sterile pipette to transfer 1.0 mL of the 

undiluted cell suspension to 99 mL of sterile PBS, cap, and mix by vigorously 

shaking the bottle a minimum of 25 times. This is cell suspension dilution “A”. 

A 1.0 mL volume of dilution “A” is 10-2 mL of the original undiluted cell 

suspension. 

B) Use a sterile pipette to transfer 11.0 mL of cell suspension dilution “A” to 99 mL 

of sterile PBS, cap, and mix by vigorously shaking the bottle a minimum of 25 

times. This is cell suspension dilution “B”. A 1.0 mL volume of dilution “B” is 

10-3 mL of the original undiluted cell suspension. 

C) Use a sterile pipette to transfer 11.0 mL of cell suspension dilution “B” to 99 

mL of sterile PBS, cap, and mix by vigorously shaking the bottle a minimum of 

25 times. This is cell suspension dilution “C”. A 1.0 mL volume of dilution “C” 

is 10-4 mL of the original undiluted cell suspension. 
Method 1611 

16

D) Use a sterile pipette to transfer 11.0 mL of cell suspension dilution “C” to 99 mL 

of sterile PBS, cap, and mix by vigorously shaking the bottle a minimum of 25 

times. This is cell suspension dilution “D”. A 1.0 mL volume of dilution “D” is 

10-5 mL of the original undiluted cell suspension. 

E) Use a sterile pipette to transfer 11.0 mL of cell suspension dilution “D” to 99 mL 

of sterile PBS, cap, and mix by vigorously shaking the bottle a minimum of 25 

times. This is cell suspension dilution “E”. A 1.0 mL volume of dilution “E” is 

10-6 mL of the original undiluted cell suspension. 

F) Prepare BHIA (Section 7.6). Ensure that agar surface is dry. Note: To ensure 

that the agar surface is dry prior to use, plates should be made several days in 

advance and stored inverted at room temperature or dried using a laminar-flow 

hood. 

G) Each of the following should be conducted in triplicate, resulting in the 

evaluation of nine spread plates: 

• Pipet 0.1 mL of dilution “C” onto surface of BHIA plate [10-5 mL (0.00001) 

of the original cell suspension]. 

• Pipet 0.1 mL of dilution “D” onto surface of BHIA plate [10-6 mL (0.000001) 

of the original cell suspension]. 

• Pipet 0.1 mL of dilution “E” onto surface of BHIA plate [10-7 mL 

(0.0000001) of the original cell suspension]. 

H) For each spread plate, use a sterile bent glass rod or spreader to distribute 

inoculum over surface of medium by rotating the dish by hand or on a rotating 

turntable. 

I) Allow inoculum to absorb into the medium completely. 

J) Invert plates and incubate at 35C ± 0.5C for 24 ± 4 hours. 

K) Count and record number of colonies per plate. Refer to the equation and Table 

3 below for calculation of undiluted cell suspension concentration. 

CFU/mLundiluted = 

CFU1 + CFU2 + .....+ CFUn

V1 + V2 + ... + Vn 

Where: 

 CFU/mLundiluted = E. faecalis CFU/mL in undiluted cell suspension 

 CFU = number of colony forming units from BHIA plates yielding 

counts within the ideal range of 30 to 300 CFU per plate 

 V = volume of undiluted sample in each BHIA plate yielding 

counts within the ideal range of 30 to 300 CFU per plate 

 n = number of plates with counts within the ideal range 

 
Method 1611 

17

Table 3. Example Calculations of E. faecalis Undiluted Cell Suspension Concentration

Examples

CFU / plate (triplicate analyses) from 

BHIA plates E. faecalis CFU / mL in undiluted 

 suspensiona

10-5 mL plates 10-6 mL plates 10-7 mL plates 

Example 1 275, 250, 301 30, 10, 5 0, 0, 0

(275+250+30) / (10-5+10-5+10-6) = 

555 / (2.1 x 10-5) = 26,428,571 = 

2.6 x 107

 CFU / mL

Example 2 TNTCb

, TNTC, 

TNTC TNTC, 299, TNTC 12, 109, 32

(299+109+32) / (10-6+10-7+10-7) = 

440 / (1.2 x 10-6) =366,666,667 = 

3.7 x 108

 CFU / mL

a Cell concentration is calculated using all plates yielding counts within the ideal range of 30 to 300 CFU per plate b

 Too numerous to count 

11.1.8 Divide remainder of undiluted cell suspension (approximately 5 mL) into 6 × 0.5 mL 

aliquots for DNA standard preparations and 100 − 200 × 0.01 mL (10 μL) aliquots for 

calibrator samples and freeze at -20C. Note: Cell suspension should be stirred while 

aliquoting. It is also recommended that separate micropipettor tips be used for each 10 μL 

aliquot transfer and that the volumes in each tip be checked visually for consistency. 

11.2 Preparation of E. faecalis genomic DNA standards

11.2.1 Remove two 0.5 mL undiluted E. faecalis cell suspensions (Section 11.1.8) from freezer 

and thaw completely. 

11.2.2 Transfer cell suspensions to extraction tubes with glass beads. 

11.2.3 Tightly close the tubes, making sure that the O-rings are seated properly. 

11.2.4 Place the tubes in bead beater and shake for 60 seconds at the maximum rate (5000 rpm). 

11.2.5 Remove the tubes from the mini bead beater and centrifuge at 12,000 × g for one minute 

to pellet the glass beads and debris. 

11.2.6 Using a 200 μL micropipettor, transfer 350 μL of the supernatants to sterile 1.7 mL 

microcentrifuge tubes. Recover supernatants without disrupting the glass beads at the 

tube bottom. 

11.2.7 Centrifuge crude supernatants at 12,000 × g for 5 minutes and transfer 300 μL of clarified 

supernatant to clean, labeled 1.7 mL low retention microcentrifuge tubes, taking care not 

to disturb the pellet. 

11.2.8 Add 1 μL of 5 μg/μL RNase A solution to each clarified supernatant, mix by vortexing 

and incubate at 37C for 1 hour. 

Note: Steps 11.2.9 - 11.2.15 may be substituted with an optional method if a DNA 

purification procedure is chosen other than the DNA-EZ purification kit. In such a 

case, manufacturer instructions should be followed rather than these steps. Continue 

onward from step 11.2.16. 

11.2.9 Add 0.6 mL of binding buffer solution from a DNA-EZ purification kit to each of the 

RNase A-treated extracts and mix by vortexing. Note: In general, a minimum 

concentration of 5 × 108

 cells is required for this step. 
Method 1611 

18

11.2.10 If using the DNA-EZ purification kit, perform the following steps. Insert one 

DNAsureTM column from the DNA-EZ purification kit into a collection tube (provided 

with kit) for each of the two extracts. Transfer the extract and binding buffer mixtures 

from Section 11.2.9 to a DNAsureTM column and collection tube assembly and 

centrifuge for 1 minute at 12,000 × g. 

11.2.11 Transfer each of the DNAsureTM columns to new collection tubes. Discard previous 

collection tubes and collected liquid. 

11.2.12 Add 500 μL EZ-Wash Buffer from the DNA-EZ purification kit to each of the 

DNAsureTM columns and centrifuge at 12,000 × g for 1 minute. Discard the liquid in 

the collection tube. 

11.2.13 Repeat step 11.2.12. 

11.2.14 Transfer each of the DNAsureTM columns to a clean, labeled 1.7 mL low retention 

microcentrifuge tube and add 50 μL of DNA elution buffer to each column. 

Centrifuge for 30 seconds at 12,000 × g. Repeat this procedure again to obtain a total 

DNA eluate volume of ~100 μL from each column. 

11.2.15 Pool the two eluates to make a total volume of approximately 200 μL. 

11.2.16 Transfer the entire purified DNA eluate volume from each column to a clean and 

sterile microcuvette for UV spectrophotometer and read absorbance at 260 and 280 

nM. (Note: The cuvette should be blanked with DNA elution buffer before reading 

sample). If necessary, the sample may be diluted with elution buffer to reach the 

minimum volume that can be accurately read by the spectrophotometer (see 

manufacturer’s recommendation), however, this may reduce the DNA concentration to 

a level that cannot be accurately read by the spectrophotometer. If available, readings 

can be taken of 2 μL aliquots of the sample with a NanoDropTM Spectrophotometer. 

11.2.17 Sample is acceptable as a standard if ratio of OD260/OD280 readings is > to 1.75. 

11.2.18 Record UV spectrophotometer results. 

11.2.19 Calculate total DNA concentration in sample by formula: 

 OD260 reading × 50 ng/μL DNA/OD260 

11.2.20 Transfer sample back to labeled 1.7 mL non-retentive microcentrifuge tube and store 

at -20C. 

11.2.21 Using total DNA concentration (Section 11.2.19), calculate E. faecalis PCR target 

sequence concentration (TSC) in purified extract (Section 9.10). 

Example: 

OD260 = 0.7271 Total DNA concentration = OD260 Reading × 50 ng/μL 

0.7271 × 50 = 36.36 ng/μL = 36.36 × 106

 fg/μL = 3.636 × 107 fg/μL 

3.636 × 107 fg/μL × 4 lsrRNA gene copies = 4.04 × 107 gene copies/μL 3.6 fg/genome genome 

11.2.22 Record UV spectrophotometer results and all calculations. 

 
Method 1611 

19

11.2.23 In appropriately labeled 1.7 mL low retention microcentrifuge tubes, perform serial 

dilutions using AE buffer to prepare DNA standards of 4 × 103

 TSC/5 μL, 4 × 102 

TSC/5 μL, 100 TSC/5 μL and 40 TSC/5 μL (see below). 

Note: Perform initial dilution of purified and quantified DNA as required to achieve a 

concentration of 2 × 108

 TSC/5 μL or 2 × 107 TSC/5 μL (as appropriate) prior to 

initiating serial dilutions. 

11.2.23.1 Perform 10-fold serial dilutions of the 2 × 108

 or 107 TSC/5 μL stock 

(10 μL : 90 μL) with AE buffer to achieve 2 × 107

 TSC/5 μL; 2 × 106 

TSC/5 μL; and 2 × 105 TSC/5 μL 

11.2.23.2 Perform 5-fold dilution of 2 × 105 TSC /5 μL stock (100 μL : 400 μL) 

with AE buffer to achieve 4 × 104

 TSC/5 μL stock 

11.2.23.3 Perform successive 10-fold serial dilutions of the 4 × 104

 TSC/5 μL stock 

(100 μL : 900 μL) to achieve 4 × 103

 TSC/5 μL; 4 × 102 TSC/5 μL stocks 

11.2.23.4 Perform a 4-fold dilution of 4 × 102 TSC/5 μL stock (100 μL : 300 μL) to 

achieve 100 TSC/5 μL stock 

11.2.23.5 Perform a final 2.5-fold dilution of the 100 TSC/5 μL stock (100 μL : 

150 μL) to achieve 40 TSC/5 μL stock 

Note: It is recommended that DNA standards be stored and manipulated 

in a different room than that used for routine sample processing in order 

to minimize the potential for laboratory contamination. 

11.2.24 Store DNA standards in refrigerator at 4°C. For long term storage, freeze aliquots at -

20°C or -80°C 

11.2.25 Generate DNA standard curves using the 40, 100, 400, and 4000 TSC/5 μL dilutions (3 

replicates each) according to Section 11.7 (ABI) or 11.8 (Cepheid), as appropriate. 

11.2.26 qPCR analyses of these diluted standards using the Enterococcus primer and probe 

assay should initially be performed at least six separate times in triplicate. From that 

point on, it is recommended that additional standard curves be generated from triplicate 

analyses of these same diluted standard samples with each new lot of TaqMan® master 

mix reagents or primers and probes to demonstrate comparable performance by these 

new reagents. 

11.3 Extraction of E. faecalis calibrator samples

11.3.1 A minimum of three calibrator extracts should be prepared during each week of 

analysis. 

Note: To prevent contamination of water sample filtrates and filter blanks, this 

procedure should be performed at a different time, and, if possible, in a different work 

station than the procedures in Sections 11.1 and 11.2 above and Section 11.5 below. 

11.3.2 Remove one tube containing a 10 μL aliquot of E. faecalis undiluted stock cell 

suspension (Section 11.1.8) from the freezer and allow to thaw completely on ice. 

Note: If using BioBalls for calibrators add a single BioBall® to each of 3, 1.0 mL sterile 

PBS blanks, filter (Section 11.4), and extract according to Section 11.5. 

11.3.3 While cell stock is thawing, using sterile (or flame-sterilized) forceps, place one 

polycarbonate filter (Section 6.14) in an extraction tube with glass beads. Prepare one 

filter for each sample to be extracted in this manner. 
Method 1611 

20

11.3.4 Dispense 590 μL of Salmon DNA/extraction buffer (Section 7.12) into three 

extraction tubes with glass beads and filters. Prepare one tube for each of the three 

calibrator samples to be extracted in this manner. Label tubes appropriately. 

11.3.5 When E. faecalis suspension has thawed, transfer 990 μL AE buffer (Section 7.11) to 

the 10 μL E. faecalis stock cell tube and mix thoroughly by vortexing. Pulse 

microcentrifuge tube briefly (1 − 2 sec.) to coalesce droplets in tube. 

11.3.6 Immediately after vortexing the E. faecalis suspension, spot 10 μL onto the 

polycarbonate filter in the extraction tube from step 11.3.4. 

Note: For the blank extraction tube, spot 10 μL AE buffer onto the polycarbonate filter 

11.3.7 Tightly close the tube, making sure that the O-ring is seated properly and label tubes 

appropriately. 

11.3.8 Repeat Sections 11.3.6 and 11.3.7 for the other two filters to prepare three calibrator 

samples with E. faecalis. 

11.3.9 Place the tubes in the mini bead beater and shake for 60 seconds at the maximum rate 

(5000 rpm). 

11.3.10 Remove the tubes from the mini bead beater and centrifuge at 12,000 × g for one 

minute to pellet the glass beads and debris. 

11.3.11 Using a 200 μL micropipettor, transfer the crude supernatant to the corresponding 

labeled sterile 1.7 mL microcentrifuge tube. Transfer 400 μL of supernatant without 

disrupting the debris pellet or glass beads at the tube bottom. Note: The filter will 

normally remain intact during the bead beating and centrifugation process. Generally, 

400 μL of supernatant can be easily collected. Collect an absolute minimum of 100 

μL of supernatant. Record volume of supernatant collected. 

11.3.12 Centrifuge at 12,000 × g for 5 minutes and transfer clarified supernatant to a clean, 

labeled 1.7 mL tube, taking care not to disturb the pellet. Note: Cell pellet may not be 

visible in calibrator samples. 

11.3.13 Label the tubes as undiluted or 1X E. faecalis calibrator extracts. Label additional 1.7 

mL tubes for 5- and 25-fold dilutions. In appropriately labeled tubes, using a 

micropipettor, add a 50 μL aliquot of each 1X E. faecalis calibrator extracts and dilute 

each with 200 μL AE buffer (Section 7.11) to make 5-fold dilutions. In appropriately 

labeled tubes using a micropipettor, add a 50 μL aliquot of each 5-fold dilution and 

dilute each with 200 μL AE buffer to make 25-fold dilutions. Store all diluted and 

undiluted extracts in refrigerator. 

11.3.14 If the extracts are not analyzed immediately, refrigerate. 

11.4 Water sample filtration

Note: It is required that minimally one water sample filtration blank (method blank) be analyzed 

for every qPCR run of water samples (Section 9.8) 

11.4.1 Place a polycarbonate filter (Section 6.14) on the filter base (shiny side "up" facing 

you), and attach the funnel to the base so that the membrane filter is now held between 

the funnel and the base. 

11.4.2 Shake the sample bottle vigorously 25 times to distribute the bacteria uniformly, and 

measure 100 mL of sample into the funnel. 

11.4.3 Filter 100 mL of water sample. After filtering the sample, rinse the sides of the funnel 

with 20 - 30 mL of sterile PBS (Section 7.4) and continue filtration until all liquid has 
Method 1611 

21

been pulled through the filter. Turn off the vacuum and remove the funnel from the 

filter base. 

11.4.4 Label an extraction tube containing glass beads (Section 6.4) to identify water sample. 

Leaving the filter on the filtration unit base, fold filter into a cylinder with the sample 

side facing inward, being careful to handle the filter only on the edges, where the filter 

has not been exposed to the sample. Insert the rolled filter into the labeled extraction 

tube with glass beads. Prepare one filter for each sample filtered in this manner. 

11.4.5 Cap the extraction tube. Refrigerate. 

11.5 DNA extraction of water sample filter extracts and method blanks

11.5.1 Using a 1000 μL micropipettor, dispense 590 μL of the Salmon DNA/extraction buffer 

(Section 7.12) into each labeled extraction tube with glass beads containing water 

sample or method blank filters from Section 11.3.4. Extract the method blank last. 

11.5.2 Tightly close the tubes, making sure that the O-ring is seated properly. 

11.5.3 Place the tubes in the mini bead beater and shake for 60 seconds at the maximum rate 

(5000 rpm). 

11.5.4 Remove the tubes from the mini bead beater and centrifuge at 12,000 × g for 1 minute 

to pellet the glass beads and debris. Note: To help prevent contamination, a new pair 

of gloves may be donned for this step, and steps 11.5.6 and 11.5.7. 

11.5.5 Using the 200 μL micropipettor, transfer 400 μL of the supernatant to a corresponding 

labeled sterile 1.7 mL microcentrifuge tube, taking care not to aspirate glass beads or 

sample debris (pellet). Note: The filter will normally remain intact during the bead 

beating and centrifugation process. Generally, 400 μL of supernatant can easily be 

collected. Collect an absolute minimum of 100 μL of supernatant. Recover the 

method blank supernatant last. 

11.5.6 Centrifuge crude supernatant from Section 11.5.5 for 5 minutes at 12,000 × g. 

Transfer 350 μL of the clarified supernatant to another 1.7 mL tube, taking care not to 

disturb the pellet. Note: Pellet may not be visible in water samples. Recover the 

method blank supernatant last. 

11.5.7 Label the tubes from Section 11.5.6 as undiluted or 1X water sample extracts with 

sample identification. These are the water sample filter extracts. Also label tubes for 

method blanks. Label additional 1.7 mL tubes for 5-fold dilutions. In appropriately 

labeled tubes, using a micropipettor, add a 50 μL aliquot of each 1X water sample 

extract and dilute each with 200 μL AE buffer (Section 7.11) to make 5-fold dilutions. 

Dilute the method blank supernatant last. 

11.5.8 Optional: For samples where the concentration of target DNA is anticipated to be 

high, an additional 25-fold dilution can be done In appropriately labeled tubes using a 

micropipettor, add a 50 μL aliquot of each 5-fold dilution and dilute each with 200 μL 

of AE buffer to make 25-fold dilutions. Dilute the method blank supernatant last. 

11.5.9 Store all diluted and undiluted extracts in refrigerator. 

11.5.10 Note: Use of 5-fold diluted samples for analysis is currently recommended if only one 

dilution can be analyzed. Analyses of undiluted water sample extracts have been 

observed to cause a significantly higher incidence of PCR inhibition while analyses of 

25-fold dilutions may unnecessarily sacrifice sensitivity. 

11.5.11 Refrigerate the extracts if they are not analyzed immediately. Water sample filter 

extracts should be analyzed the same day that they are prepared. 
Method 1611 

22

11.6 Preparation of qPCR assay mix

11.6.1 To minimize environmental DNA contamination, routinely treat all work surfaces with a 

10% bleach solution, allowing the bleach to contact the work surface for a minimum of 

15 minutes prior to rinsing with sterile water. If available, turn on UV light for 15 

minutes. After decontamination, discard gloves and replace with a new pair. 

11.6.2 Remove primers and probe stocks from the freezer and verify that they have been diluted 

to solutions of 500 μM primer and 100 μM probe. 

11.6.3 Prepare working stocks of Enterococcus, and Salmon DNA (Sketa 22) primer/probe 

mixes by adding 10 μL of each Enterococcus or Salmon DNA (Sketa 22) primer stock 

and 4 μL of respective probe stock to 676 μL of PCR-grade water, and vortex. Pulse 

centrifuge to create a pellet. Use a micropipettor with aerosol barrier tips for all liquid 

transfers. Transfer aliquots of working stocks for single day use to separate tubes and 

store at 4C. 

11.6.4 Using a micropipettor, prepare assay mix of the Enterococcus and Salmon DNA (Sketa 

22) reactions in separate, sterile, labeled 1.7 mL microcentrifuge tubes as described in 

Table 4. 

Table 4. PCR Assay Mix Composition

Reagent Volume/Sample (multiply by # samples to be analyzed per day)

Sterile H2O 1.5 μL

BSA 2.5 μL

TaqMan® master mix 12.5 μL

Primer/probe working stock 

solution 3.5 μL

Note: This will give a final concentration of 1 μM of each primer and 80 nM of probe in the 

reactions. Prepare sufficient quantity of assay mix for the number of samples to be analyzed per 

day including calibrators and negative controls plus at least two extra samples. Prepare assay 

mixes each day before handling DNA samples. 

11.6.5 Vortex the assay mix working stocks; then pulse microcentrifuge to coalesce droplets. 

Return the primer/probe working stocks and other reagents to the refrigerator. 

11.7 ABI StepOnePlusTM, ABI 7900, and ABI 7500 (all non-Fast mode) qPCR assay preparation 

(Reference 17.1)

 Transfer 20 μL of either the master mix containing Enterococcus primers and probe or the master 

mix containing the Salmon DNA primers and probe to the wells of a 96 well PCR reaction tray 

equal to number of samples to be analyzed including calibrator and negative control samples. 

(Note: The same tip can be used for pipetting multiple aliquots of the same assay mix as long as 

no contact is made with anything else). 

Example: For the analysis of 18 recreational water samples, 47 wells will require the addition of 

assay mix with Enterococcus primers and probe as follows: 18 samples, two replicates each (36), 

3 method blanks, one replicate each (3), 3 calibrators, 2 replicates each (6) and 1 no template 

control (NTC), 2 replicates (2) = 47 wells. In addition, 47 wells will require the addition of assay 

mix with Salmon DNA assay primers and probe as follows: 18 samples, two replicates each (36), 
Method 1611 

23

3 method blanks, one replicate each (3), 3 calibrators, 2 replicates each (6) and 1 NTC, 2 

replicates (2) = 47 wells. Thus a total of 94 wells are used for 18 recreational water samples. 

11.7.1 Transfer 20 μL of either the master mix containing Enterococcus primers and probe or 

the master mix containing the Salmon DNA primers and probe to wells of a 96 well 

PCR reaction tray equal to number of samples to be analyzed including calibrator and 

negative control samples. Pipet into the center of the wells, taking care to not touch 

the well walls with the pipet tip. (Note: The same tip can be used for pipetting 

multiple aliquots of the same assay mix as long as it doesn’t make contact with 

anything else). 

11.7.2 When all wells are loaded transfer to the PCR preparation station used for handling 

DNA samples (Section 6.1). Note: All aliquoting of assay mixes to reaction trays 

must be performed each day before handling of DNA samples. 

11.7.3 DNA standards − Transfer 5 μL each concentration of the undiluted DNA extracts of 

(Section 11.2.24) to separate wells of the PCR reaction tray containing Enterococcus

assay mix. Note: Record positions of each concentration. See Section 11.2.26 

regarding the frequency of DNA standard analyses. 

11.7.4 Water samples − Transfer 5 μL each of the diluted (or undiluted) DNA extracts of 

method blanks and water samples (Section 11.5.7), and corresponding dilutions of 

calibrator samples (Section 11.3.13), to separate wells of the PCR reaction tray 

containing Enterococcus assay mix. Note: Record positions of each sample. 

11.7.5 Transfer 5 μL each of the diluted (or undiluted) DNA extracts of method blanks and 

water samples (Section 11.5.7), and corresponding diluted calibrator samples (Section 

11.3.13) to separate wells of the PCR reaction tray containing Salmon DNA assay 

mix. Record positions of each sample. 

11.7.6 Transfer 5 μL aliquots of AE buffer to wells of PCR reaction tray containing 

Enterococcus master mix that are designated as NTCs. Record positions of these 

samples. 

11.7.7 Tightly cap wells of PCR reaction tray containing samples or cover tray and seal 

tightly with optical adhesive. Note: 96 well plates should be freshly prepared just prior 

to analyses. Do not prepare and refrigerate multiple plates prior to analyses, as signal 

degradation may occur. 

11.7.8 Run reactions in ABI StepOnePlusTM, ABI 7900, or ABI 7500 (all in non-Fast mode) 

Real-Time PCR Systems. For platform-specific operation see Appendix A. Note: The 

ABI 7500 Fast may be used but it should be run in the 9600 emulation mode. 

11.8 Smart Cycler® qPCR assay preparation 

11.8.1 Label 25 μL Smart Cycler® tubes with sample identifiers and assay mix type (see 

Section 11.8.8 for examples) or order tubes in rack by sample number and label rack 

with assay mix type. It is recommended that the unloaded open Smart Cycler® tubes 

be irradiated under UV light in a PCR cabinet for 15 minutes. Using a micropipettor, 

add 20 μL of the Enterococcus assay mix (Section 11.6.4) to labeled tubes. Avoid 

generating air bubbles, as they may interfere with subsequent movement of the liquid 

into the lower reaction chamber. The same tip can be used for pipetting multiple 

aliquots of the same assay mix as long as it doesn’t make contact with anything else. 

Repeat procedure for Salmon DNA (Sketa 22) assay mix. 

11.8.2 Add 5 μL of AE buffer to NTC tubes and close tubes tightly. 
Method 1611 

24

11.8.3 Close the other PCR tubes loosely and transfer to refrigerator or directly to the PCR 

preparation station used for handling DNA samples (Section 6.1). Note: All aliquoting 

of assay mixes to reaction tubes must be performed each day before handling of DNA 

samples. 

11.8.4 DNA standards − Transfer 5 μL of each concentration of the undiluted DNA extracts 

(Section 11.2.24), to tubes containing Enterococcus mix. Close each tube tightly after 

adding sample. Label the tube tops as appropriate. See Section 11.2.26 regarding the 

frequency of DNA standard analyses. 

11.8.5 Water samples − Transfer 5 μL each of the diluted (or undiluted) DNA extracts of 

method blanks and water samples (Section 11.5.7), and then corresponding dilutions 

of calibrator samples (Section 11.3.13) to tubes containing Enterococcus and Salmon 

DNA (Sketa 22) mixes. Close each tube tightly after adding sample. Load the method 

blank last. Label the tube tops as appropriate. 

11.8.6 When all Smart Cycler® tubes have been loaded, place them in a Smart Cycler®

centrifuge, and spin for 2 − 4 seconds. 

11.8.7 Inspect each tube to verify that the sample has properly filled the lower reaction 

chamber. A small concave meniscus may be visible at the top of the lower chamber, 

but no air bubbles should be present. (If the lower chamber has not been properly 

filled, carefully open and reclose the tube, and re-centrifuge). Transfer the tubes to the 

thermocycler. 

11.8.8 For platform-specific operation see Appendix B. 

11.8.9 Suggested sample analysis sequence for Smart Cycler®

 Example: For analyses on a single 16 position Smart Cycler®, calibrator samples and 

water samples will need to be analyzed in separate runs and a maximum of 6 water 

samples (or 2 replicates of 3 samples) can be analyzed per run, as described in Tables 

5 and 6, below. 

Table 5. Calibrator PCR Run - 14 Samples

Sample Description1 Quantity PCR Assay Master Mix

3 Calibrators × 2 replicates (1-, 5-, or 25-fold dilution) 6 Enterococcus

3 Calibrators × 2 replicates (1-, 5-, or 25-fold dilution) 6 Salmon DNA

No template controls (reagent blanks) 2 Enterococcus

1 Diluted equivalently to the water samples 

Table 6. Water Sample PCR Run - 14 Samples

Sample Description1 Quantity PCR Assay Master Mix

Water samples (1-, 5-, or 25-fold dilution) 6 Enterococcus

Method blank (1-, 5-, or 25-fold dilution) 1 Enterococcus

Water samples (1-, 5-, or 25-fold dilution) 6 Salmon DNA

Method blank (1- 5-, or 25-fold dilution) 1 Salmon DNA

1

 Use of 5-fold diluted samples for analysis is currently recommended if only one dilution can be analyzed. 

Analyses of undiluted water sample extracts have been observed to cause a significantly higher incidence of 

PCR inhibition while 25-fold dilutions analyses may unnecessarily sacrifice sensitivity. 
Method 1611 

25

12.0 Data Analysis and Calculations

12.1 Overview: This section describes a method for determining the ratio of the target sequence 

quantities recovered from a test (water filtrate) sample compared to those recovered from 

identically extracted calibrator samples using an arithmetic formula, referred to as the ΔΔCT 

method. The ΔΔCT relative quantitation method also normalizes these ratios for differences in 

total DNA recovery from the test and calibrator samples using qPCR analysis CT values for a 

reference sequence provided by the SPC DNA. These ratios are converted to absolute 

measurements of total target sequence quantities recovered from the test and calibrator sample 

extracts and these ratios are converted to CCEs recovered from the test samples. The complete 

procedure for determining target sequence quantities and CCEs in water samples is detailed 

below. 

12.2 Generation of CT value vs. target sequence number standard curve: Three replicate serial 

dilutions of a DNA standard, prepared as described in Section 11.2 should be prepared to give 

concentrations of 4 × 103

, 4 × 102, 1× 102, and 4 × 101 lsrRNA gene sequences per 5 μL (the 

standard sample volume added to the PCR reactions) and the replicates of each dilution pooled. 

Note: A procedure for the determinations of target sequence concentrations in the DNA standard 

is also provided in Section 9.10. 

 Aliquots of each of these dilutions should be frozen in low retention microcentrifuge tubes. 

Thawed aliquots should be stored at 4o

 C and can be reused for repeated qPCR analyses. qPCR 

analyses of these diluted standards using the Enterococcus primer and probe assay should initially 

be performed at least six separate times in triplicate. CT values from these composite analyses 

should be subjected to regression analysis against the log10-transformed target sequence numbers 

per reaction as described in Section 9.10 with example results illustrated in Figure 1. 

Figure 1: Example plot and regression analysis of qPCR analysis CT values vs. log target 

sequences per reaction. 

 AF used for subsequent comparative CT calculations (Section 12.4) can be calculated from the 

slope value of this curve by the formula AF = 10^(1 / (-)slope value). An example calculation 

using the slope value from the example regression is shown below: 

 AF = 10^ (1 / 3.41673) = 1.96 

12.3 Calculation of average target sequence recovery in calibrator sample extracts: A minimum 

of nine calibrator sample extracts should initially be prepared from at least three different freezer-
Method 1611 

26

stored aliquots of each cultured E. faecalis stock suspension that is prepared as described in 

Section 11.1. Dilutions of each of these calibrator sample extracts equivalent to the anticipated 

dilutions of the test samples used for analysis (e.g., 1-, 5- and/or 25-fold) should be analyzed with 

the Enterococcus primer and probe assay. The average CT value from these analyses should be 

interpolated on the standard curve generated from the DNA standard (Section 12.2) to determine 

the average number of target sequences per 5 μL of extract used in the reactions. An example 

calculation using an average calibrator extract CT value of 24.31 and standard curve from Figure 

1 is shown below: 

 Average calibrator target sequences/5 μL extract = 10^[(24.31-36.7194) / -3.4167] = 4285.0744 

 Note: Four places should be kept from this calculation for the following calculation (i.e., 

4285.0744). Dividing this value by 5 gives the average calibrator target sequences μL extract 

which can be multiplied by the total volume of the extract at the applicable dilution level (e.g.,

600 μL of original extract volume × 5 = 3000 μL for a 5-fold diluted sample) to determine the 

average total quantity of target sequences recovered in the calibrator sample extracts. An example 

of this calculation using the average calibrator target sequences/reaction value determined 

immediately above is shown below: 

 (4285.0744/5) × 3000 = 2571045 target sequences / total extract 

12.3.1 Calculation of average target sequence recovery per Enterococcus cell in calibrator 

sample extracts (optional): In previous studies, measurements of recreational water 

quality by the qPCR method have been reported as Enterococcus calibrator cell 

equivalents (Reference 17.4). 

12.3.2 A prerequisite for making such comparisons is to determine that the ratio of the 

numbers of target sequences recovered in calibrator sample extracts to the numbers of 

Enterococcus cells added to these samples is consistent in different studies. Example: 

The quantity of lab prepared cells added to each calibrator sample is ~100,000. 

Dividing the average target sequences recovered per calibrator extract (determined as 

described in Section 12.3) by this number provides the ratio of target sequence numbers 

to cell numbers. An example of this calculation using the average target sequences/ 

calibrator extract value determined in Section 12.3 is shown below: 

Ratio of target sequence numbers to cell numbers = 2571045/100,000 = 25.71 

12.4 Calculation of CCEs in test samples: A minimum of three fresh calibrator samples should be 

extracted and analyzed at least on a weekly basis and preferably on a daily basis in association 

with each batch of water sample filtrates. QC analysis of the results from these calibrator extracts 

should be performed as described in Section 9.11. CT values from the Enterococcus and salmon 

DNA SPC qPCR assays for both the calibrator and test samples are used in the ΔΔCT method to 

determine the ratios of target sequences in the test and calibrator sample extracts and these ratios 

are converted to CCEs recovered from the test samples as specified below and illustrated in 

Table 5. 

12.4.1 Subtract the SPC assay CT value (CT, SPC) from the target assay CT value (CT, target) for 

each calibrator sample extract to obtain ΔCT value and calculate the average ΔCT value 

for these calibrator samples. 

12.4.2 Subtract the SPC assay CT value (CT, SPC) from the target assay CT value (CT, target) for 

each water sample filtrate extract to obtain ΔCT values for each of these test samples. 

Note: If multiple analyses are performed on these samples, calculate the average ΔCT

value. 
Method 1611 

27

12.4.3 Subtract the average ΔCT value for the calibrator samples from the ΔCT value (or average 

ΔCT value) for each of the test samples to obtain ΔΔCT values. 

12.4.4 Calculate the ratio of the target sequences in the test and calibrator samples using the 

formula: AF^(-ΔΔCT), where AF = amplification factor of the target organism qPCR assay, 

determined as described in Section 12.2. 

12.4.5 Multiply the ratio of the target sequences in the test and calibrator samples by the 

estimated count (e.g., CFU) determined in Section 11.1.7 to determine the CCEs for each 

of the test samples. Note: This calculation can be applied without modification to the 

analyses of diluted extracts if both the test sample and calibrator extracts are equally 

diluted and equal volumes of diluted extracts are analyzed. 

Table 5. Example Calculations (AF = 1.96) 

Estimated 

Cell Count 1

Sample 

Type CT,target CT,SPC ΔCT ΔΔCT

Ratio calib/test 

1.96 -ΔΔCT

CCEs in Test Sample Extract 

(1.96 -ΔΔCT× Est cell count)

1200000 Calibrator 25.71 34.13 -8.42 ---- ---- 

 Test 33.74 25.94 7.8 7.59 0.006 0.006 x 1200000 = 7264.74 

1 Estimated cell count is based on plating results taking into account the dilution factor (100) and the volume 

of the dilution (0.1 mL) added to the calibrator sample 

12.4.6 The geometric mean (optional) of the CCEs and associated coefficients of variation in 

multiple water samples can be determined from individual sample CT values using the 

following procedure: 

12.4.6.1 Use ΔCT value for each individual water sample extract and the mean 

calibrator ΔCT value to calculate the CCEs in each water sample extract, as 

described above. 

12.4.6.2 Calculate the log10 of the CCEs in each water sample (log N) 

12.4.6.3 Calculate the mean (M) and standard deviation (S) from the values of log 

N obtained in the previous step for all of the water sample extracts. 

12.4.6.4 Calculate the geometric mean as 10M. 

12.4.6.5 The implied coefficient of variation (CV) is calculated, based on the log 

normal distribution, as the square root of 10V/ 0.434 - 1, where V = S2

. 

12.5 Reporting Results: Where possible, duplicate analyses should be performed on each sample. 

Report the results as Enterococcus CCEs per volume of water sample filtered. 

13.0 Sample Spiking Procedure 

13.1 Method 1611 QC requirements (Section 9) include the preparation and analysis of spiked

reference (PBS) and matrix samples in order to monitor initial and ongoing method performance. 

For the IPR (Section 9.3), OPR (Section 9.4), and MS (Section 9.5) analyses it is necessary to 

spike samples with either laboratory-prepared spiking suspensions (Section 13.3) or BioBalls 

(Section 13.7).

13.2 Preparation of Laboratory-Prepared Undiluted Spiking Suspension. Note: when using laboratoryprepared cultures, it is recommended to prepare calibrator samples and spike suspensions from 

the same culture using the same cell enumeration results (see section 11.1).
Method 1611 

28

13.2.1 Stock Culture (E. faecalis). Prepare a stock culture by inoculating a BHIA slant with E. 

faecalis ATCC® #29212TM (e.g., KWIK-STIKTM) and incubate at 35°C ± 0.5°C for 21 ± 

3 hours. This stock culture may be stored in the dark at room temperature for up to 30 

days.

13.2.2 E. faecalis Spiking Suspension (Undiluted). From the stock culture of E. faecalis

ATCC® #29212TM, transfer a small loopful of growth to the BHIB and vigorously shake a 

minimum of 25 times. Incubate at 35°C ± 0.5°C for 21 ± 3 hours. The resulting spiking 

suspension contains approximately 1.0 × 109

 enterococci CFU per mL. This is referred to 

as the “undiluted spiking suspension.”

13.2.3 Proceed to Section 13.3 for sample spiking and enumeration of spiking suspension 

(Section 13.2.2).

13.3 Laboratory-Prepared Sample Spiking and Spiking Suspension Enumeration 

Since the objective of spiking the sample is to establish percent recovery, it is necessary to 

determine the concentration of E. faecalis in the laboratory-prepared undiluted spiking suspension 

(Section 13.2.2). This section provides instructions for sample spiking (Section 13.4) and spiking 

suspension enumeration (Section 13.5). If you are using BioBalls instead of a laboratory 

preparation, go to Section 13.7. 

13.4 Sample Spiking

Please be sure to vigorously shake the spiking suspensions in the steps below to ensure accurate 

sample spiking and spiking suspension enumeration. 

13.4.1 Dilute spiking suspension

Perform steps 13.4.1.1 through 13.4.1.5 using the laboratory-prepared undiluted spiking 

suspension (Section 13.2.2). 

13.4.1.1 Mix the undiluted spiking suspension by vigorously shaking the bottle a 

minimum of 25 times. Use a sterile pipette to transfer 1.0 mL of the undiluted 

spiking suspension to 99 mL of sterile PBS; cap and mix by vigorously 

shaking the bottle a minimum of 25 times. This is spiking suspension dilution 

“A.” A 1.0 mL volume of dilution “A” is equivalent to a concentration of 1 × 

107 CFU per mL (10-2 mL of the original undiluted spiking suspension). 

13.4.1.2 Mix spiking suspension “A” (Section 13.4.1.1) by vigorously shaking the 

bottle a minimum of 25 times. Use a sterile pipette to transfer 1.0 mL to 99 

mL of sterile PBS; cap and mix by vigorously shaking the bottle a minimum 

of 25 times. This is spiking suspension dilution “B.” A 1.0 mL volume of 

dilution “B” is equivalent to a concentration of 1 × 105

 CFU per mL (10-4 mL 

of the original undiluted spiking suspension). 

13.4.1.3 Mix spiking suspension “B” (Section 13.4.1.2) by vigorously shaking the 

bottle a minimum of 25 times. Use a sterile pipette to transfer 11.0 mL to 99 

mL of sterile PBS; cap and mix by vigorously shaking the bottle a minimum 

of 25 times. This is spiking suspension dilution “C.” A 1.0 mL volume of 

dilution “C” is equivalent to a concentration of 1 × 104

 CFU per mL (10-5 mL 

of the original undiluted spiking suspension). 

13.4.1.4 Mix spiking suspension “C” (Section 13.4.1.3) by vigorously shaking the 

bottle a minimum of 25 times. Use a sterile pipette to transfer 11.0 mL to 99 

mL of sterile PBS; cap and mix by vigorously shaking the bottle a minimum 

of 25 times. This is spiking suspension dilution “D.” A 1.0 mL volume of 
Method 1611 

29

dilution “D” is equivalent to 1 × 103 CFU per mL (10-6 mL of the original 

undiluted spiking suspension). 

13.4.1.5 Mix spiking suspension “D” (Section 13.4.1.4) by vigorously shaking the 

bottle a minimum of 25 times. Use a sterile pipette to transfer 11.0 mL to 99 

mL of sterile PBS; cap and mix by vigorously shaking the bottle a minimum 

of 25 times. This is spiking suspension dilution “E.” A 1.0 mL volume of 

dilution “E” is equivalent to 1 × 102

 CFU per mL (10-7 mL of the original 

undiluted spiking suspension). 

13.4.2 Spike samples

13.4.2.1 550 CFU Spike

To spike the sample, add 5.5 mL of spiking suspension dilution “E” (Section 

13.4.1.5) to 100 mL of unspiked sample and mix by vigorously shaking the 

bottle a minimum of 25 times. This is the “spiked” sample with a 

concentration of 550 CFU per 100 mL. The volume (mL) of undiluted 

spiking suspension added is 5.5 × 10-7 mL/100 mL. This is referred to as 

Vspiked per 100 mL sample in Section 13.6.2. 

13.5 Enumeration of Spiking Suspensions (Prepared in Section 13.3.1)

13.5.1 Prepare BHIA according to manufacturer’s instructions; add 12 – 15 mL of BHIA per 

100 × 15 mm petri dish and solidify. Ensure the agar surfaces are dry. Note: Agar plates 

must be dry and free from condensation prior to use. To ensure the agar surfaces are dry, 

plates should be made several days in advance and stored inverted at room temperature or 

dried using a laminar-flow hood. 

13.5.2 Each of the following should be conducted in triplicate, resulting in the evaluation of nine 

spread plates: 

 Pipet 0.1 mL of dilution “C” (Section 13.4.1.3) onto surface of pre-dried 

BHIA plate (10-6 mL of the original spiking suspension). 

 Pipet 0.1 mL of dilution “D” (Section 13.4.1.4) onto surface of pre-dried 

BHIA plate (10-7 mL of the original spiking suspension). 

 Pipet 0.1 mL of dilution “E” (Section 13.4.1.5) onto surface of pre-dried 

BHIA plate (10-8 mL of the original spiking suspension). 

13.5.3 After pipetting the 3 spread plates for each dilution, use a sterile bent glass rod or 

spreader to distribute inoculum over the surface of the medium by rotating the dish by 

hand or on a turntable. Repeat for next 2 dilutions. Note: Please ensure that inoculum is 

evenly distributed over entire surface of the plate. 

13.5.4 Allow inoculum to absorb into the medium completely. 

13.5.5 Invert plates and incubate at 35°C ± 0.5°C for 21 ± 3 hours. 

13.5.6 Count and record number of colonies per plate. Refer to Section 13.6 for calculation of 

spiking suspension concentration. 

13.6 Calculation of Spiked E. faecalis Percent Recovery (Laboratory-Prepared Undiluted 

Spiking Suspension)

The spiked E. faecalis percent recovery will be calculated in three steps as indicated in Sections 

13.6.1 through 13.6.3 below. Note: The calculated numbers in the table examples provided below 

have been rounded at the end of each step. If your laboratory recalculates the examples using a 
Method 1611 

30

spreadsheet and rounds only after the final calculation (Section 13.6.3), the percent recovery may 

be slightly different. 

13.6.1 Calculate Concentration of E. faecalis (CFU/mL) in Undiluted Spiking Suspensions

13.6.1.1 The number of E. faecalis (CFU/mL) in the undiluted spiking suspensions will 

be calculated using all BHIA plates from Section 13.5.2 yielding counts 

within the ideal range of 30 to 300 CFU per plate. 

13.6.1.2 If the number of colonies exceeds the upper range (i.e., >300) or if the 

colonies are not discrete, results should be recorded as “too numerous to 

count” (TNTC). 

13.6.1.3 Calculate the concentration of E. faecalis (CFU/mL) in the undiluted spiking 

suspensions according to the following equation. An example calculation is 

provided in Table 6. 

E. faecalis undiluted spike = (CFU1 + CFU2 + ... + CFUn) / (V1 + V2 + ... + Vn) 

Where, 

E. faecalis undiluted spike = E. faecalis (CFU/mL) in undiluted spiking suspension 

 CFU = Number of colony forming units from BHIA plates yielding 

counts within the ideal range of 30 to 300 CFU per plate 

 V = Volume of undiluted sample on each BHIA plate yielding 

counts within the ideal range of 30 to 300 CFU per plate 

 n = Number of plates with counts within the ideal range 

 

Table 6. Example Calculation of E. faecalis Spiking Suspension Concentration

CFU / plate (triplicate analyses) from 

BHIA plates E. faecalis CFU / mL in undiluted 

spiking suspension 

(E. faecalis undiluted spike)* 10-6 mL plates 10-7 mL plates 10-8 mL plates 

TNTC, TNTC, TNTC 94, 106, 89 9, 11, 28 

(94+106+89) / (10-7+10-7+10-7) = 

289 / (3.0 × 10-7 ) = 

9.6 × 108 CFU/mL

*E. faecalis undiluted spike is calculated using all plates yielding counts within the ideal range of 30 to 300 CFU per plate

13.6.2 Calculate “True” Spiked E. faecalis (CFU/100 mL)

Calculate the true concentration of spiked E. faecalis (CFU/100 mL) according to the 

following equation. Example calculation is provided in Table 7. 

TSpiked E. faecalis = (E. faecalis undiluted spike) × (V spiked per 100 mL sample) 

Where, 

TSpiked E. faecalis = Number of spiked E. faecalis (CFU/100 mL) 

E. faecalis undiluted spike = E. faecalis (CFU/mL) in undiluted spiking suspension 

V spiked per 100 mL sample = mL of undiluted spiking suspension per 100 mL sample 
Method 1611 

31

Table 7. Example Calculation of Spiked E. faecalis

E. faecalis undiluted spike V spiked per mL sample TSpiked E. faecalis 

 9.6 × 108 CFU/mL 5.5 × 10-7 mL/100 mL of sample (9.6 × 108 CFU/mL) × (5.5 × 10-7mL /100 mL) = 528 CFU/ 100 mL 

13.6.3 Calculate Percent Recovery 

13.6.3.1 Calculate percent recovery (R) using the following equation. 

R = 100 × (Ns - Nu) 

T 

 Where, 

R = Percent recovery 

Ns = E. faecalis (CFU/100 mL) in the spiked sample 

Nu = E. faecalis (CFU/100 mL) in the unspiked sample 

 TSpiked E. faecalis = True spiked E. faecalis (CFU/100 mL) in spiked sample 

Example percent recovery calculation is provided in Table 8. 

Table 8. Example Percent Recovery Calculation 

Ns (CFU / 100 mL) Nu (CFU / 100 mL)

T Spiked E. faecalis

(CFU / 100 mL) Percent recovery (R)

521 3 a 528 100 × (521 - 3)/528 = 98% a The result of 3 CFU is acceptable if the sample was a recreational water; for PBS Nu should be <1 CFU/100 mL. 

13.7 BioBall® Sample Spiking and Enumeration 

This section provides instructions for sample spiking (Section 13.7.1) and spiking suspension 

enumeration (Section 13.7.2) using BioBalls instead of a laboratory preparation of E. faecalis. 

Upon receipt, BioBalls should be stored at -20°C. Preparation of BioBalls prior to spiking is not 

necessary, as they can be spiked directly into the sample once the vial is opened. 

13.7.1 Sample Spiking 

13.7.1.1 Open BioBall® vial by removing the cap. Aseptically add one 550 CFU E. 

faecalis BioBall® to 100 mL of sample and mix by vigorously shaking the 

bottles a minimum of 25 times. 

13.7.1.2 This is the “spiked” sample with a concentration of ~550 CFU per 100 mL 

Note: BTF provides mean and standard deviation of CFU concentrations in 

their certificates of analysis for each lot of BioBalls. These values can be 

accessed at http://www.btfbio.com/cofa.php?nav=BioBall . 
Method 1611 

32

13.7.2 Enumeration of BioBall®

13.7.2.1 Prepare BHIA according to manufacturer’s instructions. Add 12 – 15 mL of 

BHIA per 100 × 15 mm petri dish and let solidify. Ensure the agar surfaces 

are dry. Note: Agar plates must be dry and free from condensation prior to 

use. To ensure agar surfaces are dry, plates should be made several days in 

advance and stored inverted at room temperature or dried using a laminarflow hood. 

13.7.2.2 The following should be conducted in triplicate, resulting in the evaluation of 

three spread plates. 

 Open BioBall® vial by removing the cap and aseptically add one 

BioBall® to 1.0 mL of sterile PBS. Allow BioBall® to dissolve 

completely. 

 Mix suspension to homogenize. Pipet 0.1 mL of the BioBall®

suspension onto a 100 × 15 mm BHIA plate. 

13.7.2.3 For each spread plate, use a sterile bent glass rod or spreader to distribute 

BioBall® inoculum over the medium surface by rotating the dish by hand or 

on a turntable. Note: Please ensure that inoculum is evenly distributed over 

entire surface of plate. 

13.7.2.4 Allow inoculum to absorb into medium completely. 

13.7.2.5 Invert plates and incubate at 35°C ± 0.5°C for 21 ± 3 hours. 

13.7.2.6 For each dilution, count and record the sum of the number of colonies (CFU) 

on the triplicate plates. 

13.8 Calculation of BioBall® Spike Percent Recovery 

Spiked BioBall® percent recovery will be calculated using the lot mean value provided by 

manufacturer according to Section 13.8.2. Recovery may also be calculated following the two 

steps as indicated below in Sections 13.8.1 and 13.8.2. Note: The calculated numbers in the 

example provided in the tables below have been rounded at the end of each step. If your 

laboratory recalculates the examples using a spreadsheet and rounds only after the final 

calculation (Step 2), the percent recovery may be slightly different. 

13.8.1 Calculate Mean E. faecalis per BioBall® and “True” Spiked E. faecalis (CFU/100 

mL) 

The mean concentration of E. faecalis (CFU) in the BioBalls will be calculated using all 

three BHIA plates (from Section 13.7.2.6). Since one BioBall® is spiked per 100 mL 

sample, use the mean number of E. faecalis per BioBall® as the “true” spiked E. faecalis. 

For example, if the triplicate results from Section 13.7.2.6. are 57, 52, and 49, then the 

triplicate plate counts for the 550 CFU BioBall® concentration are as follows: 

TSpiked E. faecalis (CFU/100 mL) = [(54 + 52 + 49) ×10] / 3 = 517 per BioBall® 

Where, 

TSpiked E. faecalis = True spiked E. faecalis (CFU/100 mL) in spiked sample 

Thus, 517 is the “true” spiked E. faecalis (CFU/100 mL)
Method 1611 

33

13.8.2 Calculate Percent Recovery 

Calculate percent recovery (R) using the following equation: 

 R = 100 × (Ns - Nu ) 

 T 

Where, 

R = Percent recovery 

Ns = E. faecalis (CFU/100 mL) in the spiked sample (or CFU per BioBall®) 

Nu = E. faecalis (CFU/100 mL) in the unspiked sample 

TSpiked E. faecalis = True spiked E. faecalis or CFU/100 mL in spiked sample 

Percent recovery example calculation is provided in Table 9. 

Table 9. Percent Recovery Example Calculation 

Concentration Ns (CFU / 100 mL) Nu (CFU / 100 mL) T (CFU / 100 mL) Percent recovery (R) 

550 505 10 517 100 × (505 - 10)/517 = 96%

14.0 Method Performance

14.1 Multi-laboratory Validation (MLV) of Method 1611 in Marine and Fresh Water 

14.1.1 Marine Water 

14.1.1.1 Eleven volunteer laboratories participated in the U.S. Environmental 

Protection Agency’s (EPA’s) MLV study of EPA Method 1611. The 

purposes of the study were to characterize method performance across 

multiple laboratories and multiple marine water matrices, assess method 

reproducibility, and to develop QC acceptance criteria. A detailed 

description of the study and results are provided in the validation study report 

(Reference 17.9). Results submitted by laboratories were validated using a 

standardized data review process to confirm that results were generated in 

accordance with study-specific instructions and the April 2010 draft version 

of EPA Method A (1611). 

14.1.1.2 Recovery — Method 1611 was characterized by mean laboratory-specific 

recoveries, of enterococci from marine water samples spiked with BioBalls 

ranging from 68% to 841% (StepOnePlusTM) and 89% to 632% (ABI 7500), 

with an overall mean recovery of 401% (StepOnePlusTM) and 274% (ABI 

7500). Mean laboratory-specific recoveries of enterococci from PBS 

samples spiked with BioBalls ranged from 37% to 606% (StepOnePlusTM) 

and 89% to 627% (ABI 7500), with an overall mean recovery of 326% 

(StepOnePlusTM) and 297% (ABI 7500). 

14.1.1.3 Precision — Method 1611 was characterized by laboratory-specific relative 

standard deviations (RSDs) from marine water samples spiked with BioBalls 

ranging from 35% to 91% (StepOnePlusTM) and 43% to 71% (ABI 7500), 

with an overall pooled, within-laboratory RSD of 67% (StepOnePlusTM) and 
Method 1611 

34

58% (ABI 7500). For PBS samples spiked with BioBalls, laboratory-specific 

RSDs ranged from 29% to 114% (StepOnePlusTM) and 48% to 74% (ABI 

7500), with an overall pooled, within-laboratory RSD of 81% 

(StepOnePlusTM) and 58% (ABI 7500). 

14.1.1.4 Reproducibility — Each laboratory analyzed a total of five matrix samples 

received during a single week. Each sample was split into eight replicates (4 

unspiked and 4 spiked). Samples were spiked with E. faecalis (550 CFU) 

BioBalls. Overall mean recoveries were 127%, 133%, 82%, 111%, and 

228% for matrices 1 – 5, respectively. 

14.1.2 Fresh Water 

14.1.2.1 Ten volunteer laboratories participated in the U.S. Environmental Protection 

Agency’s (EPA’s) MLV study of EPA Method 1611. The purposes of the 

study were to characterize method performance across multiple laboratories 

and multiple fresh water matrices, assess method reproducibility, and to 

develop quantitative QC acceptance criteria. A detailed description of the 

study and results are provided in the validation study report (Reference 17.9). 

Results submitted by laboratories were validated using a standardized data 

review process to confirm that results were generated in accordance with 

study-specific instructions and the April 2010 draft version of EPA Method 

A (1611). 

14.1.2.2 Recovery — Method 1611 was characterized by mean laboratory-specific 

recoveries, of enterococci from fresh water samples spiked with BioBalls 

ranging from 7% to 156%, with an overall mean recovery of 83%. Mean 

laboratory-specific recoveries of enterococci from PBS samples spiked with 

BioBalls ranged from 35% to 103%, with an overall mean recovery of 69%. 

14.1.2.3 Precision — Method 1611 was characterized by laboratory-specific relative 

standard deviations (RSDs) from fresh water samples spiked with BioBalls 

ranging from 35% to 1554%, with an overall pooled, within-laboratory RSD 

of 554%. For PBS samples spiked with BioBalls, laboratory-specific RSDs 

ranged from 20% to 104%, with an overall pooled, within-laboratory RSD of 

58%. 

14.1.2.4 Reproducibility — Each laboratory analyzed a total of five matrix samples 

received during a single week. Each sample was split into eight replicates (4 

unspiked and 4 spiked). Samples were spiked with E. faecalis (550 CFU) 

BioBalls. Overall mean recoveries were 13%, 151%, 87%, 35%, and -97% 

for matrices 1 – 5, respectively. It should be noted that for Matrix #5 the 

mean background enterococci concentration was 37,329 CCEs/100 mL; 

approximately 68 times greater than the spike level of 550 cells added to 

each sample. 

15.0 Pollution Prevention

15.1 The solutions and reagents used in this method pose little threat to the environment when 

recycled and managed properly. 

15.2 Solutions and reagents should be prepared in volumes consistent with laboratory use to minimize 

the volume of expired materials to be disposed. 
Method 1611 

35

16.0 Waste Management

16.1 It is the laboratory’s responsibility to comply with all federal, state, and local regulations 

governing waste management, particularly the biohazard and hazardous waste identification rules 

and land disposal restrictions, and to protect the air, water, and land by minimizing and 

controlling all releases from fume hoods and bench operations. Compliance with all sewage 

discharge permits and regulations is also required. 

16.2 Samples, reference materials, and equipment known or suspected to have viable enterococci 

attached or contained must be sterilized prior to disposal. 

16.3 For further information on waste management, consult “The Waste Management Manual for 

Laboratory Personnel” and “Less Is Better: Laboratory Chemical Management for Waste 

Reduction,” both available from the American Chemical Society’s Department of Government 

Relations and Science Policy, 1155 16th Street NW, Washington, DC 20036. 

17.0 References

17.1 Anonymous. 1997. User Bulletin #2. ABI Prism 7700 Sequence Detection System. Foster City, 

CA, Applied Biosystems. 

17.2 Bordner, R., J.A. Winter, and P.V. Scarpino (eds.). 1978. Microbiological Methods for 

Monitoring the Environment: Water and Wastes, EPA-600/8-78-017 

17.3 Cabelli, V. J., A. P. Dufour, M. A. Levin, L. J. McCabe, and P. W. Haberman. 1979. 

Relationship of Microbial Indicators to Health Effects at Marine Bathing Beaches. Amer. Jour. 

Public Health. 69:690-696. 

17.4 Haugland, R.A., S.C. Siefring, L.J. Wymer, K.P. Brenner, and A. P. Dufour. 2005. Comparison 

of Enterococcus Density Measurements by Quantitative Polymerase Chain Reaction and 

Membrane Filter Analysis at Two Freshwater Recreational Beaches. Water Research 39:559-

568. 

17.5 Ludwig, W. and K.-H. Schleifer. 2000. How quantitative is quantitative PCR with respect to cell 

counts? System Appl. Microbiol. 23: 556-562. 

17.6 USEPA. 1983. Health Effects Criteria for Marine Recreational Waters. EPA-600/1-80-031. 

17.7 USEPA. 1984. Health Effects Criteria for Fresh Recreational Waters. EPA-600/1-84-004. 

17.8 USEPA. 1986. Ambient Water Quality Criteria for Bacteria - 1986. EPA 440/5-84-002. 

17.9 USEPA. 2011. Results of the Multi-Laboratory Validation of EPA Method A for Enterococci in 

Marine and Fresh Waters and Method B for Bacteroidales in Marine Waters by TaqMan®

Quantitative Polymerase Chain Reaction (qPCR) Assay. EPA 820-R-12-010. 

17.10 Wade, T.J., Calderon, R.L., Sams, E., Beach, M., Brenner, K.P. & Dufour, A.P. 2006. Rapidly 

measured indicators of recreational water quality are predictive of swimming associated 

gastrointestinal illness. Environmental Health Perspectives 114: 24-28. 
Method 1611 

36

18.0 Acronyms 

ΔΔCT comparative cycle threshold calculation method 

AF amplification factor 

BHIA brain heart infusion agar 

BHIB brain heart infusion broth 

BSA bovine serum albumin 

CCE calibrator cell equivalent 

CFU colony forming units 

CT cycle threshold 

CV coefficient of variation 

DNA deoxyribonucleic acid 

EDTA ethylenediaminetetraacetic acid 

GI gastrointestinal illness 

IPR initial precision and recovery 

lsrRNA large subunit ribosomal RNA (i.e., 23S rRNA) 

MS matrix spike 

MLV multi-laboratory validation 

NTC no template control 

OD optical density 

OPR ongoing precision and recovery 

PBS phosphate buffered saline 

PCR polymerase chain reaction 

QA quality assurance 

QC quality control 

qPCR quantitative polymerase chain reaction 

RNA ribonucleic acid 

RPD relative percent difference 

RSD relative standard deviation 

SLV single-laboratory validation 

SPC sample processing control 

TNTC too numerous to count 

TSC target sequence concentration 

UV ultraviolet (light) 

 
Method 1611

37

Appendix A: 

ABI StepOnePlusTM, ABI 7900, and ABI 7500 Real-Time PCR System 

Operation
Method 1611

A-1

StepOnePlusTM, ABI 7900, and ABI 7500 Real-Time PCR System 

Operation

1.0 ABI StepOnePlusTM 

1.0.1 Turn on the StepOnePlusTM and then the computer. Launch the StepOnePlusTM software 

program by double clicking on its icon on the computer desktop or from the Computer 

Programs menu. 

1.0.2 On the StepOnePlusTM home screen select Advanced Set Up. 

1.0.3 On the right side of the main screen click in the box Experiment Name, enter identifying 

information for the experiment (Name/Date etc such that experiment can be identified). 

Then go through the following fields: 

 Which instrument is going to be used to run the experiment: StepOnePlusTM

Instrument (96 wells) is default (highlighted). 

 What experiment do you want to set up: Quantitation-Standard Curve is default 

(highlighted). 

 Which reagents will be used to detect the target: TaqMan® Reagents is default 

(highlighted). 

 Which ramp speed do you want to use in the instrument run: Click on Standard-2 

hours (Not Default) 

1.0.4 Click on Plate Set Up from the navigational pane of the present screen to define the 

targets, and then assign them to wells in the reaction plate (Step 1.0.8). 

1.0.5 Define target – You can add a new target or use a saved target. By clicking on Add Saved 

Target the window with the target library will open. 

1.0.6 Select the target(s) for your assay(s) and click on Add Selected Targets. All of the 

targets may be selected simultaneously by holding the Ctrl key and highlighting the 

desired targets (e.g., Entero, Sketa). The selected targets will then be added on to the 

define target and sample screen. 

1.0.7 Optional: If a new target is to be added click the Enter Target Name cell and type the 

name. From the Reporter dropdown menu, select FAM (default). From the Quencher

dropdown menu, select Tamra (NFQ-MGB) (default). Leave the default in the color field. 

1.0.8 Click on the tab Assign Targets and Samples to see the screen view of the plate layout 

with 96 wells. 

 Select the wells, based on the plate set up, by highlighting, one target at a time. 

 Select the wells for the first target by checking the box for the desired target in Assign 

Target to the selected wells and it will automatically populate the wells for that target. 

If more than one target is being used, repeat the process above for each target. 

 The wells can be selected individually or by rows by clicking in the left corner of the 

row. In addition, the whole plate may be selected by clicking in the left corner of the 

plate. 

 To deselect a row or well press Ctrl & click the selected portion one more time and it 

will deselect the row or well. Selected wells/rows will be highlighted grey, while 

unselected wells/rows will remain white. 
Method 1611

A-2

1.0.9 Run the Method 

 On the run method screen, review the reaction volume and the thermal profile for the 

default run. If needed: The default run method can be edited or replaced with one 

from the run method library. Click either the Graphical view (default) or Tabular 

View tab. 

 Make sure the reaction volume per well field displays 25 μL, this is not the default 

setting. 

 Set the thermal profile to the following holding and cycling stages: Holding Stage 1: 

50.0°C for 2:00 minutes, Holding Stage 2: 95.0°C for 10:00 minutes, Cycling Stage: 

95.0°C for 0:15 seconds. The second step of the Cycling Stage is defaulted at 60.0°C 

for 1 minute. 

 Note: When using a run from the library click on the tab Open Run Method in the 

graphical view. Select Run Method and click ok. It will replace the default run with 

the saved run. 

1.0.10 Load the plate into the instrument. 

1.0.11 Click on the Plate Set Up tab and start the run by clicking the green button in the upper 

right hand corner of the screen. 

 Save Experiment dialogue box − Click Save to accept default file name and location 

(the name assigned when setting up the experiment). The experiment is saved by 

default to the <drive>:\ applied Biosystems\<software name>\experiment folder. 

 Run progress can be viewed from the touch screen of the instrument. At the 

beginning of a run do not leave the instrument or computer until you verify that the 

run has started.

1.0.12 Once the run is completed remove the reaction plate and discard. 

1.0.13 Analyze the run 

 Click on the tab in the top right corner of screen to Analyze the Run. 

 Highlight all of the sample wells and click on Analysis Settings to get to CT settings 

(default CT settings). 

 Highlight all the targets running in the plate; uncheck the default setting for automatic 

threshold and set the threshold to 0.03. Keep the Automatic Baseline. Click on 

Apply Analysis Settings to save changes. The new settings can be confirmed by 

viewing the threshold line on the amplification plot. 

1.0.14 Press the Export tab on the left corner of the view plate layout screen. Click on the 

browse button to find the correct place to export the data and click Start Exporting. After 

the export is done close export tool. 

1.1 ABI 7900 Real-Time PCR System Operation

1.1.1 Turn on the ABI Model 7900 and then the computer. Launch the SDS 2.2.2 software 

program by double clicking on its icon on the computer desktop or from the Computer 

Programs menu. The computer will establish communication with the 7900 instrument 

and if the connection is successful, the software will display the Connected icon in the 

status bar when a plate document is opened.
Method 1611

A-3

1.1.2 Under File menu, select New.

1.1.3 In resulting New Document window that appears, change container selection from 384

well clear plate to 96 well clear plate using drop down menu. Accept default selections 

of Absolute Quantification and Blank Template. Click OK to display a new plate 

document.

1.1.4 Click, hold and drag mouse over all PCR reaction tray wells containing samples in upper 

left window. Selected wells will be outlined with a bold line and their position numbers 

should appear in the results table in the lower left window. To unselect wells, repeat 

above process while holding down control key.

1.1.5 Above right hand window, click on Setup tab.

1.1.6 Click on Add Detector button at the bottom of the setup screen. Note: Before any 

analyses are performed, a specific detector for the method must be created. To do this, go 

to step 1.1.7. Once the detector has been created, go to step 1.1.8.

1.1.7 Click on New in the pop-up window that appears. Another pop-up window will appears. 

Under Name, type in a name for the detector that will be used by this method (e.g., 

"Method 1611"). Under Group select Default. Under Reporter select FAM. Under 

Quencher select TAMRA. Click on OK to close second pop-up window. This step only 

needs to be performed before the initial analysis run of the method. The detector that is 

named is selected in all subsequent analysis runs as indicated in step 1.1.8)

1.1.8 In pop-up window that was opened in step 1.1.6, select the desired detector under Names 

menu (e.g., Method 1611) and click on Copy to Plate Document button. Click on Done

button to return to setup screen.

1.1.9 Click on Use box next to FAM detector in right hand window. This box should become 

marked with an X. Name and color code for FAM detector should appear in each of the 

selected well positions in the upper left window and a data column for this detector should 

be created for each of the selected well positions in the results table in the lower left 

window.

1.1.10 Click on Instrument tab right hand window.

1.1.11 In instrument screen, change sample volume to 25 μL and choose 9600 emulation.

1.1.12 Still in instrument screen, click on Connect, then click on Open/Close button in lower 

right hand “Real Time” window to open PCR reaction tray holder door on instrument.

1.1.13 Insert PCR reaction tray with prepared reactions in holder.

1.1.14 Click on Open/Close button to close PCR reaction tray holder door on instrument.

1.1.15 Click on Start button in lower right hand “Real Time” window to start thermal cycling in 

instrument.

1.1.16 Name run file at prompt.

1.1.17 At termination of the run, instrument-calculated cycle threshold values should 

automatically appear for each well position and detector entry in the lower left hand 

results table window.

1.1.18 At termination of the run success complete, choose Analysis Settings from the toolbar. In 

that box enter a value for the Manual Ct Threshold (see 1.1.19). Click on OK. Click on 

Analyze from the toolbar. You should see CT values in the Results Table.
Method 1611

A-4

1.1.19 The instrument-selected threshold line is indicated by the bold red line on the plot and the 

value is listed below the window. This can be manually adjusted by either click-hold and 

dragging the line up or down or entering new values below. Note: Based on results thus 

far with the instrument, the threshold value can be adjusted from the default value of 0.2 to 

0.03, however, this should be done only if the threshold line remains above the 

background values (seen before the growth curves) for all of the samples.

1.1.20 Calculated CT values for each of the sample tray positions in the lower left hand “Results 

Table” will automatically be updated following adjustments of the threshold line. Once 

the threshold is adjusted to the desired level, select “Print Report” under the “File” menu. 

Check or uncheck desired report items by clicking on their associated boxes and the click 

on “Print” button. Note: Minimum report should have both detector boxes, i.e., “FAM” 

checked which will show CT values for all selected tray positions for this detector.

1.1.21 Export data by clicking on File from the toolbar. From the drop down menu choose 

Export. In the box you will see Look in: and here you choose a directory to send the 

exported file too. Click on Export. Save changes to document? will appear, click on 

Yes. Click OK. 

1.2 ABI 7500 (non-Fast) Sequence Detector Operation 

1.2.1 Turn on the ABI Model 7500 sequencer and then the computer. Launch the software 

program by double clicking on its icon on the computer desktop or from the Computer 

Programs menu. The computer will establish communication with the 7500 instrument. 

See “How to Set Up a New Experiment Using the ABI 7500” for screen shots. 

1.2.2 Click on either the New Experiment or Advanced Setup button to create a new 

experiment, which will pull up the Experiment Menu. 

1.2.3 From the Setup menu, select Experimental Properties to select the experiment type and 

give the experiment a name. Enter the experiment name in the asterisked box. 

 Click on 7500 (96 Wells) to select the instrument type. Note: This protocol is not 

designed for the 7500 Fast. 

 Scroll down to access more experiment properties options. Click on Quantitation – 

Standard Curve to select the experiment type 

 Click on TaqMan® Reagents to select the reagents used. 

1.2.4 From the Setup menu, select Plate Setup. Click on the Define Targets and Samples tab 

to define the reporter-quencher dye for each target and also to enter the sample 

identifications (e.g., Ent 5X). 

 Click on Add New Target and enter the name of the target. Under the Reporter 

heading, click on the drop down menu to select the reporter dye FAM. Under the 

Quencher heading, click on the drop down menu to select TAMRA as the quencher. 

 Repeat the process above to add more than one target, e.g., Sketa 5x. 

 In the Define Samples section, click on Add New Sample and enter the sample 

name in the Sample 1 box. 

 Click on the Assign Targets and Sample tab to assign the Target, sample ID and 

sample type to the wells. 

o Drag the mouse over the desired cells to assign the Target, Task and 

Sample. 
Method 1611

A-5

o While the cells are highlighted, in the Assign target(s) to the selected 

wells section, check the box under Assign for the appropriate Target, then 

under Task, select U for unknown, S for standard or N for negative 

control. 

o In the Assign sample(s) to the selected wells section, check the box 

under Assign to label the highlighted cells as Sample 1. 

 Repeat the process above, by dragging the mouse over the appropriate cells, and 

then assigning them as Unknowns, Standards or Negative Controls, as appropriate. 

Note: For Standards, in the Assign target(s) to the selected wells section, if there 

are 4 different values, each cell will need to be highlighted separately, and a quantity 

(e.g. 40000) typed in the Quantity box. 

 Click on Print Report at the top of the screen to print a plate layout for loading 

master mix and sample extracts. 

o Select Plate Layout option by clicking on the box next to it. 

o Click Print Report to print the plate layout. 

1.2.5 From the Setup menu, select Run Method to set up the thermo cycling profile. 

 In the Graphical View tab, change the Reaction Volume Per Well from the default 

50 μL to 25 μL by typing in 25. 

 Under Cycling Stage section, change the Number of Cycles to 45. 

 Check that the default settings of Temperature and Time for the two Holding Stages 

and the Cycling Stage are correct. Specifically, these should be: Holding Stage 1: 

50.0°C for 2:00 minutes, Holding Stage 2: 95.0°C for 10:00 minutes, and Cycling 

Stage: 95.0°C for 0:15 seconds. Note: The purpose of Holding Stage 1 is to 

eliminate potential PCR carryover products in the reactions using the Amp-Erase®

UNG enzyme provided in the TaqMan® Universal PCR master mix. The purpose of 

Holding Stage 2 is to inactivate the Amp-Erase® UNG enzyme. 

 The second step of the Cycling Stage is defaulted at 60.0°C for 1 minute – change 

the time to 2:00 minutes. Note: This sets the detection of the fluorescence signal to 

occur at the end of the second step in each cycle. 

 Click on Save at the top of the screen to save the run before actually running the 

experiment. 

 The Save screen will open so that you may select the folder to save the Run Data 

File. Type in the Experiment Name (if you did not already do so at the beginning of 

the Experiment Setup) and click on Save. If you had previously typed in an 

Experiment Name and there is no change, click on Save. Note: You must save to 

the hard drive (rather than a flash drive). 

1.2.6 From the Experiment menu, select Run to monitor the run in real time. 

 The Run Status screen will open - click on Start Run. When the run has 

successfully started, the Start Run button will turn change from green to red. 

1.2.7 When the run has completed, from the Setup menu, select Analysis to export your results. 

See “How to Export Results from the ABI 7500 Software” for screen shots. 

 The Analysis Settings for Experiment name screen will open. 
Method 1611

A-6

 Under the CT Settings tab, click on the Target desired to be set from Default to 

Manual Threshold setting (generally, this would be the Ent). 

 In the CT Settings for ENT section, uncheck the boxes next to Use Default 

Settings, and Automatic Threshold. Enter the desired Threshold (e.g., 0.025). If 

more than one target is present, highlight the next target (e.g., Sketa) and repeat this 

step. 

 Click on Apply Analysis Settings to save the changes. 

1.2.8 Click on Export at the top of the screen to save the experiment results data and to save the 

selected plots required in the report. The threshold value will have changed on the 

Amplification plot curve graphic. 

 The Export Data screen will open. In the Select data to export section, check all of 

the boxes (i.e., Sample Setup, Raw Data, Amplification Data, Results, and 

Multicomponent Data). 

 For Select one file or separate files, select One file to export all the data into one 

file with multiple tabs. 

 For Export File Name, enter the name of the Experimental data file to be exported, 

and for File Type, choose *.xls. 

 For Export File Location, click on Browse to select the folder in which you wish 

to export your file. Always save your file to the hard drive. 

 Click on Start Export. When this is completed, an Export Completed screen will 

open – click on Close Export Tool to complete this task. 

1.2.9 How to interpret your results. See “How to Interpret Results from the ABI 7500” for 

screen shots. 

 After exporting your data, from the Experiment menu, select Analysis.

o From the Analysis menu, select Amplification Plot to view the results of 

the selected samples at different plot settings. 

o Drag the mouse over the desired cells to select the samples to be plotted in 

the amplification plot. 

o In the Amplification Plot section, in the Plot Settings tab, select the Plot 

Type (from the drop down menu) and the Graph Type (from the drop 

down menu). 

o If the plot requires the display of the Threshold and Baseline, in the 

Options tab, check the boxes next to Threshold and Baseline. If you 

want to see the results in tabular format, click on View Well Table, and 

scroll down or sideways for more samples and analysis parameters. 

o The toolbar above the graph can be used to make hard copy prints, saving 

the file as *.jpg, zooming in and out, and changing the plot properties. 

 For the Standard Curve, select Standard Curve from the Analysis menu to view 

the results of the same sample (assuming they have the same target) and standards in 

the plot. 

o In the Plot Settings tab, click the drop down menu arrow beside Target 

to select a different target (if the standards were analyzed in more than 
Method 1611

A-7

one target), and click the drop down menu arrow beside Plot Color to 

change the plot color. 

o The standard curve parameter display below the plot (i.e. Target, Slope, 

Y-Intercept, R2

, and Eff% (percent efficiency) is useful for data analysis. 

 For Multicomponent plots, click on Multicomponent Plot from the Analysis menu 

to view the variation in the fluorescence of the dyes used in the experiment over the 

ascending repeat of the 45 thermo cycles based on well, target, or dye. 

o Click on the drop down menu arrow next to Plot Color in the Plot 

Settings tab to select the parameter for the basis of the graph (e.g., well, 

target, or dye). 

 For raw data plots, select Raw Data Plot from the Analysis menu to view the 

variation in the emission of fluorescence of the dyes in different filters present over 

the ascending repeat of the 45 thermo cycles. 

o In the Options tab, drag the pointer on the cycle scale to the desired cycle 

number to view the fluorescence variation through filters of the samples at 

that cycle. 

 For quality controls, click on QC Summary from the Analysis menu to view the 

analysis summary of the samples. 

 To view all the plots, click on Multiple Plots View from the Analysis menu to see 

all of the plots for the samples in a single window. Each plot will have its own drop 

down menu as in Section 1.2.9.5. 

1.2.10 To print the report, click on Print Report at the top of the screen. 

 Check all of the boxes (i.e., Experimental Summary, Results Summary, Plate 

Layout, Amplification Plot (3 boxes), Standard Curves, Results Table, and QC 

Summary). 

 Click on Print Report at the bottom of the screen. 
Method 1611

Appendix B: 

Cepheid Smart Cycler® Operation
Method 1611

B-1

Appendix B - Cepheid Smart Cycler® Operation 

1.0 Smart Cycler® Operation

1.1 This protocol is intended to provide only information about critical instrument settings required to 

perform EPA Method 1611. Further details concerning the operation of the instrument can be 

obtained from the Smart Cycler® Operation Manual, Cepheid Part #D0190, Rev. D. 

1.2 Turn on the Smart Cycler®; then the computer.

1.3 Double-click on the Smart Cycler® icon on the computer desktop.

1.4 The following steps for defining a protocol are only required before the initial run of the 

instrument. The protocol that is defined in these steps is used in all subsequent runs of the 

instrument. See “How to Set Up a New Experiment Using the Smart Cycler® (Software Version 

2.0” for screen shots.

1.4.1 Click on the Define Protocols icon to go to Define Protocols screen.

1.4.2 Click on the New Protocol button to open the Protocol Name? dialog. Enter "EPA 

Enterococcus Method 1611" for the new protocol name, and click OK. The protocol 

stages are defined in the series of boxes at the bottom of the Define Protocol screen. 

Make sure the new protocol is highlighted and begin to choose state settings. To define 

Stage 1, click on its drop-down box to display the menu of stage types; then select Hold. 

In the Temp column, enter 50.0, and in Secs column, enter 120, leaving the Optics setting 

as the default Off setting. (Note: This stage is performed to eliminate potential PCR 

carryover products in the reactions using the Amp-Erase® UNG enzyme provided in the 

TaqMan® Universal PCR master mix. The optical reading cannot be programmed during 

a Hold stage.).

1.4.3 To define Stage 2, click on its drop-down box to display the menu of stage types, and 

again select Hold. In the Temp column, enter 95.0, and in Secs column enter 600. Again, 

leave the Optics setting on Off. (Note: This stage is performed to inactivate the AmpErase® UNG enzyme). 

1.4.4 To define Stage 3, select 2-Temperature Cycle from its drop down menu. For the first 

step, enter 95.0 in the first row of the Temp column and 15 in the Secs column, Optics

column Off. For the second step, enter 60.0 in the second row of the Temp column, 120 

in the Secs column, and click on the Optics cell to select On from the drop-down menu. 

(Note: This sets the detection of the fluorescence signal to occur at the end of the second 

step in each cycle.) Enter 45 in the Repeat field at the top of the Stage 3 box to specify 

that it should be repeated for 45 cycles. Click the Save Protocol button.

1.4.5 To display primary curve graphs, click Define Graphs. Highlight FAM in Graph

column. Check the box for Automatically add to new runs. Under Graph Type choose 

Optics from the pull down menu. Under Channels check the box for Ch 1 (FAM). 

Under Show check the boxes for Primary Curve, Threshold (Vertical) and Threshold 

(Horizontal). Under Axes check the box for Fluorescence vs. Cycle. At the bottom of 

the screen click on Save Graph.

1.5 Click on the Create Run icon to open the Create Run screen. For each new run, enter a unique 

name in the Run Name field. (Note: The software does not allow duplicate run names). 

1.6 Enter any additional information about the run in the Notes field. Click the arrow in the Dye Set

box to display a drop-down menu of the possible selections. Select FTTC25. (Note: This selects 

the dye set: FAM, TET, Tex Red, Cy5, and a 25 μL reaction).
Method 1611

B-2

1.7 Click the Add/Remove Sites button. The Select Protocols and Sites... dialog will appear. 

Highlight (click on) the "EPA Method 1611" protocol developed prior to the first run (Section 

1.4.2) in the Protocols list. In the Sites list, highlight the sites on the instrument to be used with 

this protocol in the current run by clicking on them with the shift key held down (Note: Sites refer 

to the I-core modules in the Smart Cycler® processing block in which reaction tubes will be 

placed; a total of 16 are possible per block. When using multiple blocks, the site numbers will be 

preceded by the block letters, e.g., A, B, C); then click the right pointing arrow to transfer the 

selected sites and protocol to the Selections table.

1.8 Click on the OK button to save the selections, and return to the Create Run screen.

1.9 Place the loaded Smart Cycler® reaction tubes in the I-core module slots, selected above for 

current run. The tubes should snap into place. Either the front or back of the caps can face the 

front of the processing block.

1.10 In one of the View menus that is shown, select Analysis Settings. The displayed table includes 

one row for each of the four possible dye channels defined in the dye set. Click on the cell in the 

FAM row under the Usage column heading, and select Assay from the drop down menu. Set the 

Usage cells for all other dyes to Unused in the same manner. (Note: All assays in this protocol 

use FAM as the reporter dye). All other cells in this table should be left at default settings (See 

Smart Cycler® Operation Manual). 

1.11 In the other View menu that is shown, select the Results Table. Enter the sample identification 

information for each site in the Sample ID column (additional information can be entered into the 

Notes column.). Leave the other columns as default settings (see Smart Cycler® Operation 

Manual.)

1.12 Click on the Start Run button. The orange LEDs on the Smart Cycler® processing block should 

turn on, and the software will automatically switch to the View Results screen.

1.13 To display the real time temperature profiles for all sites, click Temperature in either of the View

menus. To display real time growth curves for all samples (i.e., the fluorescence signal vs. cycle), 

click FAM in the other View menu.

1.14 At the end of the run, it is recommended to check the cycle threshold values calculated by the 

instrument for each sample by opening the Results Table window by clicking on this selection in 

the upper View menu. It is also recommended to inspect the growth curves in the FAM window 

which can be opened in the same manner from the lower View menu. The default threshold 

fluorescence value is shown in this window as a single horizontal red line and the cycle thresholds 

for each site are shown as vertical red lines. To view the data for individual sites in this window, 

click on that site number in the table to the right of the graph. If the default threshold fluorescence 

line is well above all of the growth curve lines prior to visible amplification, the threshold 

fluorescence value can be changed to a lower value. This is done by reopening the Analysis 

Settings window from the upper View menu and entering a new value in the Manual Thresh 

Fluor Units cell in the FAM row. Conversely if the default threshold fluorescence line is below 

any of the growth curve lines prior to visible amplification, the threshold fluorescence value 

should be changed to a higher value in the same manner. Previous studies have indicated that a 

threshold value of 8 works well for most analyses. Click on the Update Analysis button to view 

the new threshold line in the FAM window. The cycle threshold values will be automatically 

updated in the Results Table.

1.15 Once the threshold fluorescence value is adjusted to an optimal value, click the Save Run button. 

(Note: The Smart Cycler® Software does not give a prompt to save changes before printing or 

exporting. Therefore, it is possible to make changes to the Results Table or Analysis Settings, and 

immediately print or export the data, then close the run without saving the changes. In this case, 
Method 1611

B-3

the data saved in the Smart Cycler® database will not match the printed or exported data. If no 

changes are made in the threshold fluorescence value, the run data is automatically saved as it is 

when the program is closed or a new run is created.)

1.16 To set up automatic export of raw data, (see “How To Set Up Automatic Export of Raw Data” for 

screen shots) from the main menu, click on Setup, then System Defaults, then Export Settings. 

From the Export Settings dialog box, check the box beside Results Table and Analysis Settings. 

Click the Browse button to select the folder where you want your raw data saved. Click on the 

radio button next to Automatic export on run completion, then click the OK button.

1.17 To manually save the Results Table and Analysis setting containing the instrument-calculated 

cycle threshold values for each sample (see “How to Manually Export Raw Data” for screen 

shots), click the Export button to display the Export Data dialog box. Check the box next to the 

heading Export Results Table and Analysis Settings by clicking on it. Leave all other boxes 

unchecked. Click on Export. A box labeled Export Data will appear with the run name in the 

file name box. Click on the drop down menu to the right of Save In: at the top left of the screen to 

change the directory where you want your data saved. Click on Save. Data are exported as 

comma-delimited text (*.cvs) files in MS Excel-compatible files to the Export folder in the Smart 

Cycler® folder: C:\Smart Cycler®\Export. Always save to the hard drive.

1.18 To archive a run in the Smart Cycler® program, click on Tools. From the drop down menu click 

on Data Management and then Archive Runs. Click Proceed. Select the run to be archived by 

clicking on its name in the database list. Click OK and then Proceed. A box labeled Archive Run

will appear on the screen. There will be a line labeled Save in:. Input which directory you would 

like the run to be saved in. There will be a line File Name:. Enter a file name. Click Save. Click 

OK.

1.19 To print run data (see “How to Print Run Data” for screen shots), after the run is completed, right 

click on the graph area, and select Print, then Print Graph with Results Table. An Optics Graph 

print preview screen will pop up, click Print. The screen will switch back to the post run screen. 

To print the generated report, click Report. A Run Report print preview screen will pop up, click 

Print. 

1.20 To set up a new analysis (see “How to Set Up a New Run” for screen shots), from the post run 

screen, click Create Run at the top left. The results of your just completed will disappear and a 

Add/Remove Sites button will appear in the middle of the screen – click it. A Select Protocols 

and Sites screen will pop up, select EPA Enterococcus Method 1611 in the Protocols box, and 

highlight the amount of sites needed for the assay (A1-A16) in the Sites box. Click the right arrow 

to the right of the sites box to move the sights to the Selections box. After double checking that 

the correct protocol is highlighted, click OK. Add the Run Name in the Run Name box. The Site 

ID, Protocol, Sample ID, Sample Type, Notes (etc.) box will pop up. Enter the Sample ID for 

each site. Under this box, find the Usage column and click on Assay to select Unused for Cy3, 

TxR and Cy5 (leave Assay for FAM). In the same box, find the Manual Thresh Fluor Units, and 

click on the units for FAM to change it from 30.0 to 8.0 (leave the units at 30.0 for Cy3, TxR and 

Cy5). After loading the Smart Cycler with tubes, click Start Run. A red light should appear on 

sites that are in use.