Genetic basis of multidrug resistance in Acinetobacter baumannii clinical isolates at a tertiary medical center in Pennsylvania.
A total of 49 unique clinical isolates of multidrug-resistant (MDR) Acinetobacter baumannii identified at a tertiary medical center in Pittsburgh, Pennsylvania, between August 2006 and September 2007 were studied for the genetic basis of their MDR phenotype. Approximately half of all A. baumannii clinical isolates identified during this period qualified as MDR, defined by nonsusceptibility to three or more of the antimicrobials routinely tested in the clinical microbiology laboratory. Among the MDR isolates, 18.4% were resistant to imipenem. The frequencies of resistance to amikacin and ciprofloxacin were high at 36.7% and 95.9%, respectively. None of the isolates was resistant to colistin or tigecycline. The presence of the carbapenemase gene bla(OXA-23) and the 16S rRNA methylase gene armA predicted high-level resistance to imipenem and amikacin, respectively. bla(OXA-23) was preceded by insertion sequence ISAba1, which likely provided a potent promoter activity for the expression of the carbapenemase gene. The structure of the transposon defined by ISAba1 differed from those reported in Europe, suggesting that ISAba1-mediated acquisition of bla(OXA-23) may occur as an independent event. Typical substitutions in the quinolone resistance-determining regions of the gyrA and parC genes were observed in the ciprofloxacin-resistant isolates. Plasmid-mediated quinolone resistance genes, including the qnr genes, were not identified. Fifty-nine percent of the MDR isolates belonged to a single clonal group over the course of the study period, as demonstrated by pulsed-field gel electrophoresis.
Adams-Haduch
Jennifer M
JM
Division of Infectious Diseases, University of Pittsburgh Medical Center, S829 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15261. doiy@dom.pitt.edu.
Paterson
David L
DL
Sidjabat
Hanna E
HE
Pasculle
Anthony W
AW
Potoski
Brian A
BA
Muto
Carlene A
CA
Harrison
Lee H
LH
Doi
Yohei
Y
D000046:Academic Medical Centers; D000151:Acinetobacter Infections / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D040981:Acinetobacter baumannii / Q000187:drug effects* / Q000235:genetics* / Q000302:isolation & purification / Q000472:pathogenicity; D000583:Amikacin / Q000494:pharmacology; D001483:Base Sequence; D003428:Cross Infection / Q000188:drug therapy / Q000453:epidemiology / Q000382:microbiology; D017931:DNA Primers / Q000235:genetics; D024901:Drug Resistance, Multiple, Bacterial / Q000235:genetics*; D016521:Electrophoresis, Gel, Pulsed-Field; D005798:Genes, Bacterial; D006801:Humans; D008826:Microbial Sensitivity Tests; D017720:Molecular Epidemiology; D010414:Pennsylvania; D016133:Polymerase Chain Reaction; D001618:beta-Lactamases / Q000235:genetics
D017931:DNA Primers; D000583:Amikacin; D001618:beta-Lactamases