1596. Molecular Detection of Antimicrobial Susceptibility: Changing Paradigm of Laboratory Testing for Multidrug Resistant Organisms
Session: Poster Abstract Session: Diagnostics for Multidrug-Resistant Bacteria
Saturday, October 10, 2015
Room: Poster Hall
Background: The increasing threat of antibiotic resistance is of worldwide public health concern.  Empirical therapy for treatment of infectious diseases has helped create bacterial strains with multiple antibiotic resistance mechanisms.  Rapid molecular testing can offer a change in paradigm for susceptibility testing and can have a significant impact on patient care. In this study, a molecular diagnostic panel was designed to screen for twenty-six multidrug resistance genes encoding the most clinically prevalent mechanisms of resistance to four major classes of antibiotics:  aminoglycosides, β-lactams, fluoroquinolones, and macrolides. 

Methods:  TaqMan® Assays were designed for use on a high-throughput real-time platform (QuantStudio® 12K Flex).  DNA was isolated from samples using a KingFisher™ Flex instrument, followed by twelve-step cycling with a panel-specific PreAmp mix.  Pre-amplification products were then processed on custom OpenArray® Real-Time PCR Plates.

Results:  The target specificity of TaqMan® Assays were validated using clinical isolates (n=109) with known, sequence-validated resistance profiles and patient samples (n=517) for which phenotypic data was available.  Clinical isolates yielded 100% correlation when compared to resistance profiles.  One isolate, characterized as blaNDM-1 positive, was not detected by this panel, but repeated sequencing indicated loss of the NDM-1 plasmid.  Screening of patient samples revealed a complex pattern of up to fourteen genes encoding resistance for four major classes of antibiotics, with TEM and ermA-C being the most prevalent (48% and 91% in respiratory and gastrointestinal samples, respectively).  CTX-M Groups 1, 2, and 9; SHV; ACT/MIR; and qnrA and qnrS were also detected.

Conclusion:    Molecular testing is a practical approach for the rapid detection of drug resistance. While phenotypic susceptibility methods are widely accepted in clinical practice, these tests are laborious, time-consuming, and results may be subjective.  The direct testing for multidrug resistant organisms with a high-throughput TaqMan® Assay panel provides a powerful screening tool that can be utilized in clinical settings to improve antibiotic stewardship programs and improve patient care.

Leslie Malone, MS, MB(ASCP)CM1, Megan Stonebraker, BS1, Stefan Brzezinski, MBA, BS1, Donald Stalons, PhD, D(ABMM), MPH1, Ali Hassoun, MD FIDSA FACP2, Pius Brozka, PhD3, Nicole Fantin, BS3, Kamini Varma, PhD3, Joshua Trotta, BA3 and Elena Grigorenko, PhD4, (1)Diatherix Laboratories, Inc., Huntsville, AL, (2)Alabama Infectious Diseases Center, Huntsville, AL, (3)Thermo Fisher Scientific, South San Francisco, CA, (4)Diatherix Laboratories, Inc, Huntsville, AL


L. Malone, Diatherix Lab: Investigator , Salary

M. Stonebraker, Diatherix Laboratories, Inc.: Employee , Salary

S. Brzezinski, Diatherix lab: Employee , Salary

D. Stalons, Diatherix Lab: Investigator , Salary

A. Hassoun, None

P. Brozka, Thermo Fisher: Employee , Salary

N. Fantin, Thermo fisher: Employee , Salary

K. Varma, Thermo fisher: Employee , Salary

J. Trotta, Thermo fisher: Employee , Salary

E. Grigorenko, Diatherix lab: Investigator , Salary

Findings in the abstracts are embargoed until 12:01 a.m. PDT, Wednesday Oct. 7th with the exception of research findings presented at the IDWeek press conferences.