Understanding molecular features of carbapenem-resistant Acinetobacter baumannii causing invasive infection through comparative genomics and their clinical implications

Abstract

Acinetobacter baumannii is a highly potent nosocomial pathogen, associated with increased in-hospital mortality. Here, we investigated the changes in the molecular characteristics of carbapenem-resistant A. baumannii (CRAB) isolated from the blood samples of patients admitted to a tertiary hospital in South Korea from January 2009 to July 2015. Whole genome sequencing (WGS) using the Illumina MiSeq platform and multi-locus sequence typing (MLST) were performed for 98 CRAB clinical isolates. Antimicrobial resistance genes were identified by querying contig sequences against ResFinder database. The distribution of virulence factors was obtained using Large Scale blast score ratio (LS-BSR). Epidemiologic data were collected from hospital database. MLST using Oxford scheme revealed 10 sequence types of CRAB, of which ST191 was the dominant type (n = 59). Although blaOXA-23 was shared by most analysed strains, the composition of antimicrobial resistance determinants was different among the sequence types. ST447 and ST451/ST1809 with a few resistance genes were isolated during the later years of the study period. Number of virulence genes increased, while that of ST191 did not changed significantly during the investigation period. MLST types, composition of antimicrobial resistance genes, and virulence genes had no association with clinical outcomes of CRAB bacteraemia. In conclusion, the active change in or accumulation of antimicrobial resistance determinants and virulence genes in CRAB was not observed during the research period. The molecular characteristics of CRAB had no association with clinical outcomes of CRAB bacteraemia.