1425. Mapping the Genetic Lineages of Acinetobacter baumannii (Ab) at a Metropolitan Academic Hospital in Northeast Ohio (NEO); a 15 Year Comparison
Session: Poster Abstract Session: Epidemiology of Multiple Drug-Resistant Gram Negative Rods
Saturday, October 20, 2012
Room: SDCC Poster Hall F-H
Background: Ab has been a challenge to clinicians in the NEO area for more than a decade.  When Ab first emerged in an academic metropolitan hospital in the mid 1990s, this pathogen was regarded as an infection control dilemma with low associated mortality. Recently, we experienced an outbreak of carbapenem resistant Ab, including 5 bloodstream infections (BSI) that resulted in mortality. We hypothesized that this outbreak was caused by a different strain of Ab. In this analysis, we compare the molecular characteristics of Ab involved in two distinct outbreaks that occurred in this hospital in NEO in 1996 and 2010-11.

Methods: 21 Ab isolates archived from 1996 and 31 between August 2010 and March 2011 were examined. Antimicrobial susceptibility was tested with broth microdilution. Genetic typing was done with automated repetitive sequence-based PCR (rep-PCR). Isolates were considered clonally related if they were >95% similar by the method of Kullback-Leibler (K-L). Representative isolates belonging to clonal lineages designated as worldwide clones (WW) 1, 2 and 3 were included as references. To detect the presence of acquired carbapenemases as a mechanism of carbapenem resistance, PCR was performed with primers that anneal to blaOXA-23, blaOXA-24, and blaIMP.

Results: Among isolates from 1996, resistance to imipenem and ampicillin/sulbactam was 4.75% (1/21) and 9.5% (2/21), respectively. In contrast, among isolates from 2010-11, resistance to imipenem was 87% (27/31) and 71% (22/31) to ampicillin/sulbactam. Molecular typing with rep-PCR and analyzed with K-L method revealed that 74% (16/21) of isolates from 1996 belong to a cluster related to WW 3, whereas 68% (21/31) of the 2010-11 isolates (including 5 BSI isolates) belong to a cluster related to WW 2 that harbored blaOXA-23. Additionally, we discovered a cluster of 2 isolates harbored blaOXA-24. Of note, 2 isolates from 1996 were indistinguishable from the predominant group in 2010-11.

Conclusion: We demonstrate that carbapenem-resistant Ab from the WW 2 clonal lineage and harboring blaOXA-23/24 predominates in this metropolitan hospital in NEO, displacing a pre-existent WW 3-related strain that was carbapenem susceptible. In this setting, strain replacement and the introduction of carbapenemase genes may have a major impact on patient outcomes.

Federico Perez, MD1, Jennifer Hanrahan, DO2, Sue Rudin, BS1, Robert Kalayjian, MD3 and Robert A. Bonomo, MD1, (1)Louis Stokes Cleveland Veterans Affairs Medical Center, Cleveland, OH, (2)MetroHealth, Cleveland, OH, (3)The MetroHealth Medical Center, Cleveland, OH


F. Perez, None

J. Hanrahan, None

S. Rudin, None

R. Kalayjian, None

R. A. Bonomo, Pfizer: Grant Investigator, Grant recipient
AstraZeneca: Grant Investigator, Grant recipient
Rib-X: Grant Investigator, Grant recipient

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