Molecular epidemiology of emerging bla _OXA-23-Like - and bla _OXA-24-Like -carrying acinetobacter baumannii in Taiwan

The rate of recovery of carbapenem-resistant Acinetobacter baumannii (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 bla _OXA-23-like or bla _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 bla _OXA-23-like or bla _OXA-24-like were subjected to pulsed-field gel electrophoresis, and 82 isolates (60 isolates with bla _OXA-23-like and 22 isolates with bla _OXA-24-like ) were selected for multilocus sequence typing to determine the sequence type (ST) and clonal group (CG) and for detection of additional -lactamase and aminoglycoside resistance genes. The flanking regions of carbapenem and aminoglycoside resistance genes were identified by PCR mapping and sequencing. The localization of bla _OXA was determined by S1 nuclease and I-CeuI assays. The numbers of CRAB isolates carrying bla _OXA-23-like or bla _OXA-24-like , especially those carrying bla _OXA-23-like , increased significantly from 2008 onward. The bla _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 bla _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. Tn6180-borne armA was found in 74 (90.2%) CRAB isolates, and 58 (70.7%) isolates had Tn6179 upstream, constituting AbGRI3. bla _TEM was present in 38 (46.3%) of the CRAB isolates tested, with 35 (92.1%) isolates containing bla _TEM in AbGRI2-type structures, and 61% of ampC genes had ISAba1 upstream. We conclude that the dissemination and spread of a few dominant lineages of CRAB containing various resistance island structures occurred in Taiwan.