Molecular Epidemiology of Emerging blaOXA-23-Like- and blaOXA-24-Lik-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 beta-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.