Whole-genome shotgun sequences of seven colistin-resistant Acinetobacter baumannii isolates from bacteraemia.

OBJECTIVES: Acinetobacter baumannii is a nosocomial pathogen responsible for various infections, including bloodstream infections, meningitis and ventilator-associated pneumonia. It is resistant to most antimicrobial agents, including colistin, and the development of colistin-resistant A. baumannii is of serious concern in the hospital setting. In this study, the whole-genome shotgun sequences of seven colistin-resistant A. baumannii isolates from bloodstream infections were characterised.

METHODS: Colistin susceptibility testing was performed by broth microdilution. Whole genomes of all seven isolates were sequenced using an Ion Torrent™ PGM platform with 400-bp chemistry.

RESULTS: All seven isolates were confirmed to be resistant to colistin, with minimum inhibitory concentrations (MICs) ranging from 8μg/mL to 64μg/mL. Various antimicrobial resistance genes were present. The mcr1-5 genes were absent in all seven isolates. Chromosomal mutations that could be responsible for colistin resistance were observed. Six isolates belonged to ST848 and one isolate belonged to ST451.

CONCLUSION: Increased colistin resistance among clinical isolates of A. baumannii is alarming. Several mutations that could be responsible for colistin resistance were observed in all seven isolates. However, the significant contribution of these mutations requires further confirmation. However, genome information for these colistin-resistant A. baumannii isolates will be helpful for further comparative analysis.