The molecular epidemiology and antimicrobial resistance phenotypes of Acinetobacter baumannii isolated from patients in three hospitals in southern Vietnam

Multidrug resistance (MDR) in the nosocomial pathogen Acinetobacter baumannii limits therapeutic options and impacts on clinical care. Resistance against carbapenems, a group of last-resort antimicrobials for treating MDR A. baumannii infections, is associated with the expression (and over-expression) of carbapenemases encoded by the blaOXA genes. The aim of this study was to determine the prevalence of antimicrobial resistant A. baumannii associated with infection in three hospitals in southern Vietnam and to characterise the genetic determinants associated with resistance against carbapenems. We recovered a total of 160 A. baumannii isolates from clinical samples collected in three hospitals in southern Vietnam from 2012 to 2014. Antimicrobial resistance was common; 119/160 (74%) of isolates were both MDR and extensively drug resistant (XDR). High-level imipenem resistance (>32µg/ml) was determined for 109/117 (91.6%) of the XDR imipenem non-susceptible organisms, of which the majority (86.7%) harboured the blaOXA-51 and blaOXA-23 genes associated with an ISAba1 element. Multiple-locus variable number tandem repeat analysis (MLVA) segregated the 160 A. baumannii into 107 different MLVA types, which described five major clusters. The biggest cluster was a clonal complex comprised mainly of imipenem resistant organisms that were isolated from all three of the study hospitals. Our study indicates a very high prevalence of MDR/XDR A. baumannii causing clinically significant infections in hospitals in southern Vietnam. These organisms commonly harboured the blaOXA-23 gene with ISAba1 and were carbapenem resistant; this resistance phenotype may explain their continued selection and on-going transmission within the Vietnamese healthcare system.