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

Nguyen Tuan Anh,Nguyen Si Tuan,Stephen Baker,Ho Huynh Thuy Duong,Tran Vu Thieu Nga,Dao Minh Y,Nguyen Van Vinh Chau,Huynh Minh Tuan

doi:10.1099/jmm.0.000418

Abstract

Multidrug resistance 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 multidrug-resistant (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 characterize 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 (>32 µg ml-1) was determined for 109/117 (91.6 %) of the XDR imipenem-nonsusceptible 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 segregated the 160 A. baumannii into 107 different multiple-locus variable number tandem repeat analysis types, which described five major clusters. The biggest cluster was a clonal complex composed 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 ongoing transmission within the Vietnamese healthcare system.

Highlights

Acinetobacter baumannii has emerged globally as one of the leading causes of nosocomial infections
The 160 A. baumannii isolates from three hospitals during the period of investigation were recovered from sputum (64/160; 40 %), pus (8/160; 5 %), blood (3/160; 1.9 %) and fluid aspirates (3/160; 1.9 %); data regarding the origins of the additional clinical isolates (82/160, 51.3 %), which were predominantly from hospital C, were not available
Antimicrobial susceptibility testing was performed within the hospital laboratories at the time of isolation; 17 differing antimicrobials were tested, with only 5 antimicrobials consistently tested between the three sites

Summary

Introduction

Acinetobacter baumannii has emerged globally as one of the leading causes of nosocomial infections. This emergence is partly associated with the remarkable ability of the organism to become resistant to multiple antimicrobials, which leaves limited treatment options [1]. The use of carbapenems as last-resort antimicrobials for the treatment of A. baumannii infections has been hindered by the rapid development of resistance against this important group of antimicrobials [2,3,4]. Carbapenem resistance in A. baumannii is associated with a variety of mechanisms, but expression (and overexpression) of carbapenemases plays the most important role [5, 6]. The presence of specific insertion elements, such as an ISAba, upstream of these blaOXA genes leads to the up-regulation of their expression, resulting in further decreased susceptibility against carbapenems [9, 10]

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