Molecular epidemiology and characterization of multiple drug-resistant (MDR) clinical isolates of Acinetobacter baumannii

Summary Objectives The aim of this study was to identify the genetic relatedness of multiple drug-resistant (MDR) Acinetobacter baumannii clinical isolates recovered from a hospital in Los Angeles. Methods Twenty-one MDR A. baumannii isolates were collected and their antibiotic susceptibilities determined according to Clinical and Laboratory Standards Institute guidelines. Genes coding for antibiotic resistance were identified by PCR, and their identities were confirmed by DNA sequencing. Clonal relationships were studied by pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST). Results MDR consistently correlated with the presence of oxacillinases, mostly in the form of the plasmid-mediated OXA-23 enzyme, which was detected in 12 (57.1%) isolates. GES-type carbapenemases were found in 20 (95.2%) strains, AAC in all 21 (100%) strains, and PER in seven (33.3%) strains, and IS Aba1 was detected in 16 (76.2%) isolates. The association between IS Aba1 and resistance genes confirms insertion elements as a source of β-lactamase production. Of the 21 clinical isolates, five were found to be related to sequence type 1 (ST1) and 16 to ST2, as analyzed by MLST. PFGE demonstrated that the majority of clinical isolates were highly related (>85%). Conclusions This study supports a more complete understanding of genotyping of antibiotic resistance for better assessment of MDR strain transmission.