1799. Comparison of Multidrug Resistant Gram Negative Pathogen Detection by Culture and PCR from Surveillance Samples
Session: Poster Abstract Session: Resistant Gram-Negative Infections: CRE Epidemiology
Saturday, October 10, 2015
Room: Poster Hall
Posters
  • 2015 ID Week ICU Screen.D Schora.pdf (400.3 kB)
  • Background:

    Rapid detection of Gram negative multidrug resistant organisms (MDRO) in patient surveillance samples is important for infection prevention.  Culture methods are considered less sensitive than PCR and can take longer to obtain, but PCR only detects the targets in the assay.  We compared real-time PCR testing for CTX-M, KPC and NDM-1 from multiple body sites to culture for MDRO Enterobacteriaceae. We hypothesized that PCR testing would be the same or superior to culture and could replace it.

    Methods:

    Samples of throat, axilla and peri-anus were collected from ICU patients. For culture, swabs were plated to agar with ceftazidime and incubated overnight. Organisms were identified and susceptibility testing was performed to determine if MDRO. For PCR, a swab from each sample was incubated overnight in 10ml Tryptic Soy Broth with a 30µg ceftriaxone disc. The broth was then tested for  blaNDM,  blaKPC and blaCTX-M as previously described by Mangold  (J Clin Micro 2013;51:3423-5 and J Clin Micro 2011;49:3338-9). Culture results were compared to PCR and discrepancies resolved. For colonies confirmed as MDRO but negative by PCR, we investigated the presence of other beta lactamase genes that might account for resistance. A multiplex PCR for TEM, SHV or OXA plasmids was performed as described previously (J Antimicrobial Chemother 2010; 65:490-5).

    Results:

    1191 samples were collected from 4/1/2013 to 6/30/2014. Thirty patients were PCR positive/culture negative, but 25 were subsequently grown from the broth where the PCR test was taken, confirming the PCR result. Additionally, culture grew 23 MDRO not detected by the designed PCR assay (12 TEM, 9 SHV, 2 mixed OXA:SHV producers), yielding 120 true positives.

    Table. Performance of PCR and Culture for MDRO

     

    PCR

    Culture

    True Positive

    96

    95

    False Positive

    5

    0

    False Negative

    24

    25

    Sensitivity

    80.0%

    79.2%

    Specificity

    99.5%

    100%

    PPV

    95.0%

    100%

    NPV

    97.8%

    97.7%

    Conclusion:

    PCR recovered more of the targeted MDR Gram negative bacteria than direct culture (p<0.001), but including all possible MDROs indicated no difference in performance (p=1). PCR is an important tool for infection prevention, but the broad range of genotypes responsible for Gram-negative MDROs challenge this as a single approach for effective surveillance.

    Donna Schora, MT(ASCP)1, Barbara Voss, BS1, Kathy Mangold, PhD1, Sanchita Das, MD1, Richard Thomson Jr., PhD1, Irene Dusich, MT(ASCP)1, Marc-Oliver Wright, MT(ASCP), MS, CIC2, Becky Smith, MD2 and Lance Peterson, MD, FIDSA, FSHEA1, (1)NorthShore University HealthSystem, Evanston, IL, (2)Infection Control, NorthShore University HealthSystem, Evanston, IL

    Disclosures:

    D. Schora, None

    B. Voss, None

    K. Mangold, None

    S. Das, None

    R. Thomson Jr., None

    I. Dusich, None

    M. O. Wright, None

    B. Smith, None

    L. Peterson, None

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