Molecular epidemiology and carbapenem resistance characteristics of Acinetobacter baumannii causing bloodstream infection from 2009 to 2018 in northwest China

Abstract

Bloodstream infection (BSI) caused by <i>Acinetobacter baumannii</i> poses a serious threat to health and is correlated with high mortality in patients with hospital-acquired infections, so the molecular epidemiology and antimicrobial resistance characteristics of this pathogen urgently need to be explored. <i>A. baumannii</i> isolates from BSI patients were collected in three tertiary hospitals in northwest China from 2009 to 2018. Antimicrobial susceptibility testing was used to determine the MICs of the <i>A. baumannii</i> isolates. Whole-genome sequencing based on the Illumina platform was performed for molecular epidemiological analyses and acquired resistance gene screening. The efflux pump phenotype was detected by examining the influence of an efflux pump inhibitor. The expression of efflux pump genes was evaluated by RT-PCR. In total, 47 <i>A. baumannii</i> isolates causing BSI were collected and they presented multidrug resistance, including resistance to carbapenems. Clone complex (CC) 92 was the most prevalent with 30 isolates, among which a cluster was observed in the phylogenetic tree based on the core genome multi-locus sequence type, indicating the dissemination of a dominant clone. BSI-related <i>A. baumannii</i> isolates normally harbour multiple resistance determinants, of which oxacillinase genes are most common. Except for the intrinsic <i>bla</i> _OXA-51 family, there are some carbapenem-resistant determinants in these <i>A. baumannii</i> isolates, including <i>bla</i> _OXA-23, which is encoded within the Tn<i>2006</i>, Tn<i>2008</i> or Tn<i>2009</i> transposon structures and <i>bla</i> _OXA-72. The transfer of <i>bla</i> _OXA-72 was suggested by XerC/D site-specific recombination. The AdeABC efflux pump system contributed to carbapenem resistance in <i>A. baumannii</i> isolates, as evidenced by the high expression of some of its encoding genes. Both the clone dissemination and carbapenem resistance mediated by oxacillinase or efflux pumps suggest an effective strategy for hospital infection control.