# Presentation: 719959

## Detecting Antimicrobial Resistance A Partnership of PHL and CDC

- Roberta B. Carey
- Branch Chief, Epidemiology and Laboratory
- Division of Healthcare Quality Promotion
- CDC

## Objectives

- Understand the clinical and public health importance of resistant microorganisms
- Learn what organisms are the most important to monitor
- Recognize the pitfalls in susceptibility testing for detecting resistant bacteria
- Know the requirements for sending organisms to CDC
- Understand how PHL and CDC can work together to facilitate rapid reporting of results

## MDRSP

- VRE

- MDRTB

- ESBL

## Why are we seeing more resistance?

- Overuse of antibiotics for viral illness
- Under-treating infections
- Stop taking medication before finished
- Use less potent antibiotics in underdeveloped countries
- Millions of dollars of antibiotics incorporated into livestock feed to        bring a better price in the market

## How does this affect public health?

- Resistant bacteria transmitted person-to-person perpetuate disease
- Nosocomial- hospital
- Community- daycare, nursing homes
- No antibiotics left to use!!
- Only 8 new agents approved since 1998
- Deadly combination of virulence and resistance
- Resistant organisms in one part of the world only a plane ride away from your world

## MRSA

- Methicillin resistant *Staphylococcus aureus*  resistant to all penicillinase resistant antibiotics (nafcillin, oxacillin, dicloxacillin)
- Use oxacillin to predict resistance since it is more stable
- If ox R, then cephalosporin R, amp/sulbactam R
- Population of *S. aureus* is heterogeneous which makes detection of resistance difficult
- Tests to detect *mecA* gene or its product altered PBP2a more accurate

## MRSA

- Common in healthcare setting, now in    outpatient population with skin/soft tissue infections, necrotizing pneumonia, septicemia
- Daycare centers, football and wrestling teams, jails/prisons, msm
- Unique PFGE type USA300
- Different *mecA* gene (*mec* type IV)
- Carries the gene for Panton -Valentine leukocidin (PVL)
- Clindamycin for therapy requires additional testing to check for inducible resistance (D zone test)
- Nasal colonization facilitates spread of *S. aureus*

## VRSA / 

- Vancomycin-resistant *S. aureus* and vancomycin-intermediate *S. aureus*
- Public health issue since vancomycin is routinely used to treat MRSA
- 3 strains of VRSA: MI, PA, NY
*S.aureus* acquired the *vanA* gene from enterococci
- Surveillance revealed no transmission
- All potential VRSA and VISA (vanc > 4 μg/ml, growth on vancomcyin screening agar) should be sent to CDC for confirmation ASAP

## VA

**Vancomycin MIC =128 ****μg/ml**

***S. aureus***** #595 tested in reference BMD panel**

- Increasing concentrations of vancomycin

**VA**

## S. aureus #595 tested after overnight growth on BAP 

***S. aureus***** #595 tested after overnight growth on BAP **

## Brain Heart Infusion agar containing 6 μg/ml of vancomycin (BHI-V6)

**Brain Heart Infusion agar containing 6 ****μg/ml of vancomycin (BHI-V6)**

***S. aureus***** #595 grown O/N on **_**BAP**_

***S. aureus***** #595 grown O/N on **
_**BHI-V6**_

**QC *****E. faecalis***** ATCC 51299**

## Algorithm for Testing S. aureus with Vancomycin (VA)

**Algorithm for Testing *****S. aureus***** with Vancomycin (VA)**

**Acceptable**
**Primary Test Methods**
**Include:**

**Disk diffusion****2**** **_**plus**_** VA screen plate**
- (BHIA with 6 μg/ml of VA)

**VA MIC **_**<**_**2 ****μ****g/ml**
**And NO growth on**
**VA screen plate**

**VA MIC **_**<**_**2 ****μ****g/ml**
**AND GROWTH on**
**VA screen plate**
**(rare)**

**VA MIC **_**>**_**4 ****μ****g/ml**
**AND GROWTH on**
**VA screen plate**

**VA zone **_**<**_**14 mm**
** ****AND GROWTH on **
**VA screen plate**

**VA zone >14 mm **
**AND GROWTH on**
**VA screen plate**

**Report as VSSA****3**

**Report as VSSA****3**

**Possible VISA/VRSA**

**CHECK purity**

**SAVE ISOLATE**

**NOTIFY infection control, physician, local health department and CDC****5**** of “possible VISA/VRSA”**

**MIC method****1**** **_**plus**_** VA screen plate**
- (BHIA with 6 μg/ml of VA)

**Possible VISA/VRSA**

**VA zone >14 mm**
**and NO growth on**
**VA screen plate**

**CONFIRM isolate ID**

**RETEST using non-automated MIC method****4**

**SEND to reference laboratory for confirmation**

_**Important Footnotes**_
**1****Laboratories using automated susceptibility test methods should add a commercial vancomycin agar screen plate. **
**2****Disk diffusion alone is not sufficient to detect VISA.**
**3****If a laboratory is concerned about a result based on a patient’s history, MIC testing can be performed at CDC.****	****	**
**4 ****Non-automated methods: reference broth microdilution, agar dilution, agar gradient diffusion (Etest; use a 0.5 McFarland inoculum and Mueller-Hinton agar)**.
**5****Report to CDC by email: SEARCH@cdc.gov**

**April 2004**

- More VISA/VRSA info: www.cdc.gov/ncidod/hip/vanco/vanco.htm

## VRE

- Vancomycin-resistant enterococci                   (*E. faecium* and *E. faecalis*)
- Dangerous mix of already resistant bugs now resistant to the most widely prescribed antibiotic used to treat Gram positive infections
- Enterococci important cause of nosocomial bacteremia, surgical site infection and UTI
- Spread in healthcare environment on hands of personnel or contact with contaminated objects
- Treatment with new antibiotics (linezolid, quinopristin/dalfopristin)

## Biochemical Tests to ID Enterococci

**Biochemical Tests to ID Enterococci**

## Additional Tests

**Additional Tests**
**to Detect Species with Intrinsic Vancomycin Resistance**

## Pneumococci

- Pen R pneumococci

- MDRSP

## Slide 17

## MDRSP

- Multidrug resistant Streptococcus pneumoniae
- Resistant to pen, SXT, erythromycin, tetracycline, third generation cephalosporins
- Resistant organisms easily spread in daycare settings
- New polysaccharide conjugate vaccine with 7 most common serotypes of pneumococci seen in children protects vaccinated and those around them (herd effect)

## ESBL

- Extended spectrum beta lactamases destroy activity of all penicillins, cephalosporins, aztreonam
- Clinical importance
- High failure rates with ESBLs treated with cephalosporins
- ESBL producing organisms significant infection control problems
*E. coli, Klebsiella *spp*., Proteus mirabilis, Salmonella*
- Carbapenems (imipenem) drug of choice

## ESBL

- Screen for resistance based on MIC _>_2 μg/ml or disk diffusion zone sizes
- Must perform confirmatory tests using clavulanic acid to reverse activity _>_3 fold decrease in MIC or 5mm increase
- If positive, change S/I to R for all cephalosporins

**14 mm**

**20 mm**

**ceftazidime**

**ceftaz/clav**

## AmpC Beta lactamases

- Chromosomal mediated in *Enterobacter, Serratia, Citrobaccter, Morganella, Providencia*
- Plasmid-mediated in *E. coli* and *Klebsiella*
- Enzymes are resistant to the effects of beta-lactamase inhibitors
- Enzymes hydrolyze cephalosporins and cephamycins (cefoxitin and cefotetan)
- No standardized method of detection in the lab

## MDR GNR

*Acinetobacter baumannii* resistant to all routinely used antibiotics
*Klebsiella* resistant to imipenem and cephalosporins
- Resistance to > 3 classes of antibiotics in *Ps*. *aeruginosa* increased from 4% in 1993 to 14% in 2002
- Inappropriate empiric treatment group had 38.4% mortality rate compared 27.4% for patients given at least one active antibiotic

## How do clinical labs detect resistance?

- Large labs with high volume testing use automated instruments for ID/susceptibility
- Rapid results, labor saving
- May sacrifice accuracy, limited flexibility of antibiotics tested
- Disk diffusion
- Technically simple
- More cumbersome, slower to get a result
- E test
- Combines MIC and diffusion method
- Labor intensive and costly

## Pitfalls in Current Susceptibility Testing

- Automation may overcall MRSA
- Automation may not detect VRSA
- Automation does not detect inducible resistance in clindamycin
- Disk diffusion may not detect VRE and VISA
- ESBL detection requires confirmatory testing
- Interpretation of pneumococcal antibiotics depends on meningitis or non-meningitis

## How can PHL help?

- First line resource to the smaller clinical labs
- Disseminate accurate advice
- Perform reference testing to confirm unusual results
- Gather data to track area-wide resistance
- Compile state-wide antibiogram

## How can PHL be a good partner with CDC?

- Provide required information about the isolate
- Patient demographics
- Specimen source
- Growth requirements of the organism (temperature, atmosphere, media)
- Biochemical reactions of your testing
- Give your “best guess” so it goes to the right lab
- Your name and phone number at PHL

## Microbiologist name and phone

**Microbiologist name and phone**

**Get phone # of submitting lab/doctor**

** **

**Best guess**

**Must  check  a **
**Box !!**

**Agar, temp, atmosp**

## Copy of your biochemical reactions or the submitting laboratory.  Tell us anything and everything !!

**Copy of your biochemical reactions or the submitting laboratory.  Tell us anything and everything !!**

## How can PHL be a good partner with CDC?

- Check isolate for **purity** before it’s sent !!!!
- Use selective agars to find contamination
- Chocolate, MacConkey, CNA, bile esculin
- If you are unsure of the importance or urgency of a request, call CDC
- Staph lab  		404-639-3570
- Strep lab   		404-639-1237
- Enterics  		404-639-2316
- Anaerobes 		404-639-3654
- Special bacti		404-639-5458
- E.coli/Shigella  		404-639-4372