Genotypic and Phenotypic Correlations of Multidrug-Resistant Acinetobacter baumannii-A. calcoaceticus Complex Strains Isolated from Patients at the National Naval Medical Center

Authors: HUANG, XIAO-ZHE - Walter Reed Army Institute; Frye, Jonathan; CHAHINE, MOHAMAD - Walter Reed Army Institute; CASH, DANA - Walter Reed Army Institute; BARBER, MELISSA - Walter Reed Army Medical Center; BABEL, BRITTA - Us Naval Medical Research Center; KASPER, MATTHEW - Us Naval Medical Research Center; WHITMAN, TIMOTHY - Us Naval Medical Research Center; LINDLER, LUTHER - US Department Of Health And Human Services (HHS); BOWDEN, ROBERT - Walter Reed Army Institute; NIKOLICH, MIKELJON - Walter Reed Army Institute

Submitted to: Journal of Clinical Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/25/2010
Publication Date: 11/1/2010
Citation: Huang, X., Frye, J.G., Chahine, M.A., Cash, D.M., Barbe, M.G., Babel, B.S., Kasper, M.R., Whitman, T.J., Lindler, L.E., Bowden, R.A. 2010. Genotypic and Phenotypic Correlations of Multidrug-Resistant Acinetobacter baumannii-A. calcoaceticus Complex Strains Isolated from Patients at the National Naval Medical Center. Journal of Clinical Microbiology. 48(11):4333-4336.

Interpretive Summary: Acinetobacter baumannii-calcoaceticus complex (ABC) is a bacterium that causes wound infections in many combat casualties. An increase in ABC strains which are resistant to antibiotics has complicate treatment of these wounds. In this study, 102 ABC isolates from wounded soldiers treated at National Naval Medical Center (NNMC) were characterized to determine how closely the matched on a genetic level. Pulse field gel electrophoresis (PFGE) is a technique that was used to classify them into 23 distinct PFGE types (PFTs). Eighty percent (n=82) of the isolates belonged to six PFTs; the remaining isolates (n=20) belonged in the other 17 PFTs. Microarray analysis of representatives of the eight major PFTs detected the presence of several antimicrobial resistance genes. Isolates with the blaOXA gene were found to be resistant by in vitro susceptibility testing to the important antibiotic, imipenem. Further analysis by DNA sequencing determined that the imipenem resistant gene was blaOXA-23. Isolates with this gene clustered into two distinct PFTs. These data provided precise information that benefits diagnosis including development of rapid identification tests, surveillance, and epidemiology of MDR ABC infections which are important when determining treatment protocols.

Technical Abstract: Acinetobacter baumannii-calcoaceticus complex (ABC) infections have complicated the care of U.S. combat casualties. In this study, 102 ABC isolates from wounded soldiers treated at National Naval Medical Center (NNMC) were characterized by phenotype and genotype to identify clones in this population and to determine their genetic relationship. Pulse field gel electrophoresis (PFGE) revealed 23 PFGE types (PFTs) based on > 90% similarity. Eighty percent of the isolates belonged to six dominant PFTs while the remaining isolates had limited similarity to other isolates. Microarray analysis of DNA extracted from eight representative isolates of the dominant PFGE patterns detected 11 aminoglycoside resistance genes, 4 ß-lactamase genes and 11 other antimicrobial resistant (AR) related genes encoding sulfonamide resistance, tetracycline resistance and DNA transfer associated genes. Only isolates hybridizing with a probe for a blaOXA gene were resistant to imipenem. PCR and sequencing analysis of these isolates determined that the imipenem resistant gene was blaOXA-23. Further PCR analysis showed that 27% of the 102 ABC isolates were blaOXA-23 positive. Drug susceptibility tests and a PCR test correlated well, indicating 93% of imipenem resistant isolates carried the blaOXA-23 locus. Isolates harboring blaOXA-23 tended to cluster into two distinct PFTs, with 17 isolates belonging to PFT 5 and 10 isolates belonging to PFT 11. Molecular characterization by PFGE, DNA microarray and PCR combined with classical susceptibility testing provided precise MDR information that can benefit diagnosis including development of rapid identification tests, surveillance, epidemiologic analysis, and preventive strategies for MDR ABC infections.