United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 1 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

1. Purpose

To provide standard procedures for screening USDA/AMS Microbiological Data Program (MDP) 

samples for Salmonella using the Vitek® Immuno Diagnostic Assay System (VIDAS®). 

2. Scope

This SOP shall be followed by all laboratories conducting microbiological studies for MDP, 

including support laboratories conducting non-routine activities. This SOP represents minimum 

MDP requirements and is presented as a general guideline. Each laboratory shall have written 

procedures that provide specific details concerning how the procedure is implemented in that 

laboratory.

3. Principle

The VIDAS®is an automated system developed by bioMérieux for detecting microorganisms 

isolated from food, environmental, and clinical samples. The reliability and accuracy of 

detecting the presence of a target organism are a result of the specific antigen-antibody reactions 

coupled to an enzyme linked fluorescent assay (ELFA) and monitored by a colorimeter. 

4. References

4.1 Wallace Andrews and T. S. Hammack. Bacteriological Analytical Manual, Chapter 

5. Salmonella, http://www.cfsan.fda.gov/~ebam/bam-5.html (last accessed 04/12/05).

 4.2 VIDAS®Instrument and PC User Guide, bioMerieux

 4.3 VIDAS Salmonella (SLM) package insert, 12/2007, bioMerieux

4.4 Curiale, M.S., Gangar, V. and Gravens, C. 1997. VIDAS®enzyme-linked 

immunofluorescent assay for detection of Salmonella in food: collaborative study. 

Journal of AOAC International, Volume 80, No.3, pp. 491-504.

4.5 Maijala R, Johansson T, and Hirn J. 1992. Growth of Salmonella and competing flora in 

five commercial RV media. International Journal of Food Microbiology. Volume17, pp.1-8.

 4.6 SOP MDP-DATA-01, Record Keeping and Results Reporting.

 4.7 SOP MDP-LABOP-02, Sample Receipt, Elution, Preenrichment, and DNA Extraction
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 2 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

 4.8 SOP MDP-MTH-04, Detection of Salmonella in Fresh Produce by Bax®PCR.

4.9 SOP MDP-MTH-10, Isolation and Identification of Salmonella using Cultural 

Methods

 4.10 SOP MDP-QA-03, Quality Assurance Controls.

5. Procedures

5.1 VIDAS®- Follow the manufacturer’s instructions for proper use of this instrument and 

follow the VIDAS®Salmonella (SLM) kit insert for kit use, kit controls use and kit storage. 

Allow all kit components to reach room temperature before use.

NOTE: All Salmonella spp. are pathogenic to humans and pose a serious health risk. Always 

handle samples, pure cultures and controls with extreme care and follow standard safety practices 

and procedures.

5.2 Equipment and Materials 

 VIDAS®Instrument, bioMérieux

 VIDAS®Salmonella (SLM) assay kit reference number 30 702, bioMérieux

 Water bath set to 42 ± 0.5°C 

 VIDAS® Heat and Go, or water bath set at 95-100°C

 Pipettor (100-1000μl)

 Serological pipets, sterile, 1 ml

 5.3 Media and Reagents

 Rappaport-Vassiliadis (RV) broth: 16 x 150 mm sterile test tubes containing 10mL 

aliquots. (RV broth by Oxoid has been shown to provide better enrichment of 

Salmonella compared to RV produced by other manufacturers. Therefore, Oxoid RV 

broth is recommended).

 Tetrathionate (TT) broth (with iodine and brilliant green): 16 x 150 mm sterile test 

tubes containing 10mL aliquots (On the day the medium is used, add 20mL iodine 

solution per 1L basal broth and 10mL brilliant green solution per 1L basal broth.)
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 3 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

 M broth: 16 x 150 mm test tubes containing 10 mL aliquots

 Preenriched samples and controls from SOP MDP-LABOP-02

5.4 Controls (Specific strains are listed in SOP MDP-QA-03) - Carry all controls through 

this entire procedure, including any necessary cultural confirmation. If any of the controls 

fail to yield a satisfactory result, refer to SOP MDP-QA-03.

 Negative culture control: E. coli (MDP 017) from SOP MDP-LABOP-02

 Positive culture control: Salmonella typhimurium (MDP 014) from SOP MDPLABOP-02

 Uninoculated media control from SOP MDP-LABOP-02

 Positive Produce Control from SOP MDP-LABOP-02.

 Manufacturer’s supplied VIDAS®Salmonella (SLM)standards(S1) and controls(C1 

and C2)

5.5 Pre-enrichment - Refer to SOP MDP-LABOP-02 for pre-enrichment of all commodities. 

Use these test cultures for this SOP.

5.6 Post Enrichment

5.6.1 Gently mix pre-enriched samples and controls from 6.5 above or from BAX®

preliminary positive enrichments.

5.6.2 Transfer 0.1mL of the culture suspension into 10 mL RV broth. Incubate in a 42

± 0.5°C water bath for 18-24 h.

5.6.3 In parallel, transfer 1.0 mL of the culture suspension into 10 mL TT broth and 

incubate tubes in a 42 ± 0.5°C water bath for 18-24 h.

5.6.4 Following incubation, mix selective enrichment broths and transfer 1 mL from 

the RV broth into 10mL M broth. In addition, transfer 1 mL from the TT broth into 

another 10 mL M-broth. 
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 4 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

5.6.5 Incubate both M-broth samples at 42 ± 0.5 oC for 6-8 h. After incubation, M 

broths can be stored at 2-8

oC up to 48 hrsif the VIDAS®

analysis cannot be performed 

immediately.

5.7 VIDAS® Analysis

5.7.1 Following incubation, remove the M broth cultures and mix well.

5.7.2 For VIDAS® Heat and Go use, transfer 250 μl from each of the two M broth 

cultures into the sample well of one appropriately labeled SLM VIDAS®strip. Repeat 

this for each sample and controls. Do not heat the S1 or C1/C2 kit controls. Heat the 

sample for 15 minutes. Refer to VIDAS® Heat and Go instruction manual for proper 

use and strip placement. Cool the strips to room temperature before VIDAS®analysis.

5.7.3 For water bath use, transfer 1mL each of the two M-broth cultures into a separate 

sterile test tube. Repeat this for each sample and controls. Do not heat the S1 or C1/C2 

kit controls. Heat the samples and control tubes containing 2mL M broth by 

submerging below the broth level in a boiling waterbath for 15 min.

5.7.4 Cool sampled and controlsto room temperature (20-25C). Mix the contents of 

the tube and pipet 500μl from the heat-killed sample/control tube into the sample well 

of the appropriately labeled SLM VIDAS®strip.

5.7.5 Mix the S1 kit standards (if necessary) and the C1 and C2 kit controls. Pipet

500μL of the each standard (in duplicate strips) and C1, C2 control into the sample 

well of the appropriately labeled SLM VIDAS®Strip.

5.7.6 Perform the VIDAS®analysis according to manufacturer’s instructions.

5.8 Interpretation of Results

5.8.1 Once the assay is completed, results are analyzed automatically by the 

instrument. Two fluorescence measurements in the Reagent Strip’s optical 

cuvette are taken for each specimen tested. The first reading is a background 

reading of each substrate cuvette before the SPR is introduced into the substrate. 

The second reading is taken after incubating the substrate with the enzyme 

remaining on the interior of the SPR. The relative fluorescence value (RFV) is 
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 5 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

calculated by subtracting the background reading from the final result. The 

calculation appears on the result sheet. 

5.8.2 A report is printed which records the type of test performed, test sample 

identification, analyst initials, date and time, lot number and expiration date of 

reagent kit being used and each test’s RFV, Test Value, and interpreted result.

5.8.3 Test results are reported as invalid when the background reading is above 

predetermined cutoff value indicating low-level substrate contamination. In such 

a case, the VIDAS®portion of the analysis shall be repeated.

5.8.4 The RFV obtained for each sample is interpreted by the VIDASsoftware 

as follows:

 Thresholds and Interpretations

Test Value Threshold Interpretation

<0.23 Negative

0.23 Positive

5.8.5 Samples with test values greater than or equal to the threshold value are 

reported as positive for Salmonella and shall be confirmed culturally. Refer to 

SOP MDP-MTH-04 and SOP MDP-MTH-10.

5.8.6 Samples with test values lower than the threshold value indicate samples 

with undetectable Salmonella antigen.

5.9 Reporting

5.9.1 A preliminary positive is defined as a positive VIDAS®reading.

5.9.2 Data shall be reported according to SOP MDP-DATA-01.
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 6 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

5.10 Transfer and Storage of Cultures - Refer to SOP MDP-SHIP-03 for archival 

procedures and shipping of isolates.

Disclaimer: Reference to brand names (kits, equipment, media, reagents, etc.) does not constitute 

endorsement by this agency. 
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 7 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

Mary Tijerina 25 Sep 09

Revised by: Mary Tijerina Date

Microbiologist, Monitoring Programs Office

8609 Sudley Road, Suite 206

Manassas, VA 20110

(703) 330-2300 x111

Maya Achen 25 Sep 09

___________________________________________________________

Approved By: Maya Achen Date

Chairperson, MDP Technical Advisory Group

Ohio Department of Agriculture

Consumer Analytical Laboratory, Bldg 3

8995 E Main St

Reynoldsburg, OH 43068

(614) 728-2790

Diana Haynes 25 Sep 09

Approved By: Diana Haynes Date

Deputy Director, Monitoring Programs Office

8609 Sudley Road, Suite 206

Manassas, VA 20110

(703) 330-2300 x134

ORIGINAL SIGNATURE PAGE MAINTAINED BY USDA, AMS, SCIENCE & TECHNOLOGY, MONITORING PROGRAMS OFFICE

ELECTRONICALLY REPRODUCED SIGNATURES
United States Department of Agriculture

Agricultural Marketing Service, Science & Technology

Microbiological Data Program

SOP No: MDP-MTH-09 Page 8 of 8

Title: Detection of Salmonella Using VIDAS® Method 

Revision: 1 Replaces: 02/09/09 Effective: 09/25/09

Revision 1 September 2009 Monitoring Programs Office

 Updated References, Section 4.

 Revised Sections 5.1 through 5.10