1624. A single genotype of multidrug resistant (MDR) Acinetobacter baumannii expresses multiple antibiotic susceptibility phenotypes
Session: Poster Abstract Session: Multidrug-Resistant Gram Negative Rods
Saturday, October 5, 2013
Room: The Moscone Center: Poster Hall C

In the absence of genetic fingerprinting data, it is common practice for infection preventionists and hospital epidemiologists to define, as a single genotype, bacteria with equal antibiotic susceptibility phenotypes.  Evidence to support this practice of “predicting genotypes” based on antibiotic susceptibility phenotypes is scarce.  The objective of this study was to describe the utility of using antibiotic susceptibility phenotypes to define a single genotype of MDR Acinetobacter baumannii.


Clinical isolates were collected from patients infected or colonized with MDR A. baumannii from a long-term acute care hospital in Louisville, Kentucky.  Broth microdilution in cation-adjusted Mueller-Hinton broth was used to determine the minimum inhibitory concentrations (MICs) for 21 antibiotics.  Organisms with equal antibiotic susceptibility phenotypes were considered to correlate to a single “predicted genotype”.  REP-PCR was used to determine genotypes. 


A total of 21 MDR A. baumannii isolates from a single genotype were included in the analysis.  Based on antibiotic susceptibility phenotypes, a total of 15 “predicted genotypes” were identified. The maximum number of isolates with equal antibiotic susceptibility phenotypes was four. 


This study indicates that the antibiotic resistance phenotype does not predict the genotype of A. baumannii.  During an outbreak investigation, the practice of predicting bacterial genotypes based on antimicrobial phenotypes should be discouraged.

Timothy L. Wiemken, PhD, MPH, CIC1, Susan Rudin, BS2, Michael Jacobs, MD3, Robert A. Bonomo, MD2, Robert Kelley, PhD1, Emily Pacholski, MPHc4 and Julio Ramirez, MD1, (1)Division of Infectious Diseases, University of Louisville, Louisville, KY, (2)Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, (3)Case Western Reserve University/University Hospitals of Cleveland, Cleveland, OH, (4)Infectious Diseases, University of Louisville, Louisville, KY


T. L. Wiemken, None

S. Rudin, None

M. Jacobs, None

R. A. Bonomo, None

R. Kelley, None

E. Pacholski, None

J. Ramirez, None

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