Molecular epidemiology and genetic characterisation of carbapenem-resistant Acinetobacter baumannii isolates from Guangdong Province, South China

Carbapenem-resistant Acinetobacter baumannii (CRAB) has become a worldwide issue. This study aimed to characterise the epidemiology and genetic relationships of A. baumannii isolates in Guangdong Province, China.CRAB isolates were collected from five municipal hospitals from June-December 2017. The 16S-23S rRNA intergenic spacer region was used for confirmation of strain identity. Antimicrobial susceptibility testing and the CarbAcineto NP test were performed to analyse the resistance spectrum and carbapenemase production of the isolates. PCR-based assays were used to detect β-lactamase genes and related mobile genetic elements. Genetic diversity among the isolates was analysed by enterobacterial repetitive intergenic consensus (ERIC)-PCR, multilocus sequence typing (MLST) and multiplex PCR.A total of 122 isolates were confirmed as A. baumannii; all were resistant to the tested antibiotics except for tigecycline and colistin. The CarbAcineto NP test showed that 93.4% of the isolates produced a carbapenemase. blaOXA-23-like and extended-spectrum β-lactamase-encoding genes were found by PCR in 94.3% and 91.8% of the isolates, respectively. Furthermore, the genetic environment of blaOXA-23-like was mainly associated with transposons Tn2008 (46.1%), Tn2006 (27.0%) and Tn2009 (20.9%). MLST identified six existing sequence types (STs) and three novel STs, of which ST195 (35.7%) and ST208 (32.1%) were the most common, belonging to clonal group 92 and European clone II.This study suggests that co-production of β-lactamases was the major resistance mechanism of CRAB isolates. Dissemination of blaOXA-23-like may be facilitated by transposable elements. ST195 and ST208 were the predominant epidemic types of A. baumannii in Guangdong Province.