Wide dissemination of OXA-23-producing carbapenem-resistant Acinetobacter baumannii clonal complex 22 in multiple cities of China

In this study, multilocus sequence typing (MLST) was used to describe the genetic backgrounds of carbapenem-resistant Acinetobacter baumannii (CRAB) and carbapenem-susceptible A. baumannii (CSAB) from multiple cities of China. One hundred and fifty-two CRAB and 74 CSAB isolates obtained from 16 cities of China were selected for molecular characterization by MLST. eBURST was used to cluster sequence types (STs) into clonal complex (CCs) and infer evolutionary descent. PCR was used to detect carbapenemase-encoding genes and bla(AmpC) with the upstream element ISAba1. CSAB showed more diverse genetic backgrounds than CRAB since 36 distinct STs were identified in CSAB while only 8 STs were identified in CRAB. ST22 and its three single-locus variants, all clustered into CC22, were the most prominent STs, accounting for 86.8% of CRAB and 45.9% of CSAB, distributed in all 16 cities and possessing more noticeable antibiotic resistance than other STs. PCR amplification was positive for bla(OXA-23) in most CRAB isolates but negative in CSAB isolates. The presence of ISAba1 upstream of bla(AmpC) was variable in distinct STs of CRAB. eBURST reveals that CC22 is the largest group in the Pubmlst database, which also contains ST6 previously identified in a European clone II isolate as a member of a subgroup of CC22. We describe the wide dissemination of CRAB CC22 in China. The close relatedness between CC22 and European clone II implies the probable global spread of CC22. It is inferred that ST22-CSAB evolves to ST22-CRAB through acquiring bla(OXA-23) as a determinative factor.