Molecular Epidemiology of Emerging <i>bla</i> _OXA-23-Like - and <i>bla</i> _OXA-24-Like -Carrying Acinetobacter baumannii in Taiwan

Abstract

The rate of recovery of carbapenem-resistant <i>Acinetobacter baumannii</i> (CRAB) isolates has increased significantly in recent decades in Taiwan. This study investigated the molecular epidemiology of CRAB with a focus on the mechanisms of resistance and spread in isolates with <i>bla</i>_OXA-23-like or <i>bla</i>_OXA-24-like All 555 CRAB isolates in our multicenter collection, which were recovered from 2002 to 2010, were tested for the presence of class A, B, and D carbapenemase genes. All isolates with <i>bla</i>_OXA-23-like or <i>bla</i>_OXA-24-like were subjected to pulsed-field gel electrophoresis, and 82 isolates (60 isolates with <i>bla</i>_OXA-23-like and 22 isolates with <i>bla</i>_OXA-24-like) were selected for multilocus sequence typing to determine the sequence type (ST) and clonal group (CG) and for detection of additional β-lactamase and aminoglycoside resistance genes. The flanking regions of carbapenem and aminoglycoside resistance genes were identified by PCR mapping and sequencing. The localization of <i>bla</i>_OXA was determined by S1 nuclease and I-CeuI assays. The numbers of CRAB isolates carrying <i>bla</i>_OXA-23-like or <i>bla</i>_OXA-24-like, especially those carrying <i>bla</i>_OXA-23-like, increased significantly from 2008 onward. The <i>bla</i>_OXA-23-like gene was carried by antibiotic resistance genomic island 1 (AbGRI1)-type structures located on plasmids and/or the chromosome in isolates of different STs (CG92 and novel CG786), whereas <i>bla</i>_OXA-24-like was carried on plasmids in CRAB isolates of limited STs (CG92). No class A or B carbapenemase genes were identified. Multiple aminoglycoside resistance genes coexisted in CRAB. Tn<i>6180</i>-borne <i>armA</i> was found in 74 (90.2%) CRAB isolates, and 58 (70.7%) isolates had Tn<i>6179</i> upstream, constituting AbGRI3. <i>bla</i>_TEM was present in 38 (46.3%) of the CRAB isolates tested, with 35 (92.1%) isolates containing <i>bla</i>_TEM in AbGRI2-type structures, and 61% of <i>ampC</i> genes had IS<i>Aba1</i> upstream. We conclude that the dissemination and spread of a few dominant lineages of CRAB containing various resistance island structures occurred in Taiwan.