Abstract
Acinetobacter baumannii is a highly potent nosocomial pathogen that is associated with increased in-hospital mortality. Here, we investigated the changes in 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 using the Illumina MiSeq platform and multi-locus sequence typing (MLST) were performed for 98 CRAB clinical isolates. In silico analyses for the prediction of antimicrobial resistance and virulence factor genes were performed. Plasmid sequences, including complete forms, were reconstructed from the sequence reads. Epidemiologic data were collected from the hospital database. MLST using the 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 compositions of antimicrobial resistance determinants differed among sequence types. ST447 and ST451/ST1809 with a few resistance genes were isolated during the later years of the study period. The number of virulence genes increased, while that of ST191 did not change significantly over the investigation period. Intriguingly MLST types, compositions of antimicrobial resistance genes, and virulence genes had no association with clinical outcomes of CRAB bacteraemia. In conclusion, active changes in or accumulations of antimicrobial resistance determinants and virulence genes in CRAB were not observed during the research period. Molecular characteristics of CRAB had no association with clinical outcomes of CRAB bacteraemia.
Highlights
Acinetobacter baumannii is an aerobic gram-negative coccobacillus known for relatively few virulence factors as compared to other gram-negative pathogens [1]
An multi-locus sequence typing (MLST) using Pasteur scheme identified 93 strains (94.9%) that were classified into ST2, indicating that most of the strains belonged to IC II
We found that 91 strains (92.9%), all belonging to IC II, had two incidences of gdhB alleles, 3 and 189, which made distinctions between ST208, ST1806, ST451, and ST1809 ambiguous
Summary
Acinetobacter baumannii is an aerobic gram-negative coccobacillus known for relatively few virulence factors as compared to other gram-negative pathogens [1]. Its ability to acquire various antimicrobial resistance genes makes it a highly successful nosocomial pathogen, which is associated with increased in-hospital mortality [2]. The specific clone, international clone 2 (IC II), is a major clonal group among Korean CRAB isolates [5]. This organism is associated with nosocomial outbreaks and multidrug resistance in association with blaOXA-23-like genes [6]. 75% of A. baumannii clinical isolates were shown to belong to IC II in Korea [7], and IC II was recognised as the second most common cause of bacteraemia from 2012 to 2013 [8]
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