Isolation and Whole-genome Sequence Analysis of the Imipenem Heteroresistant Acinetobacter baumannii Clinical Isolate HRAB-85

- We isolated/characterised an imipenem heteroresistant A. baumannii strain (HRAB-85).
- Subpopulations grew in the presence of imipenem at concentrations of up to 64 μg/mL.
- The total length of strain HRAB-85 was 4,098,585 bp with a GC content of 39.98%.
- Whole-genome sequencing revealed four ISs and 19 antibiotic-resistance genes.
- Our results improve our understanding of heteroresistant A. baumannii.

ObjectivesHeteroresistance is a phenomenon in which there are various responses to antibiotics from bacterial cells within the same population. Here, we isolated and characterised an imipenem heteroresistant Acinetobacter baumannii strain (HRAB-85).MethodsThe genome of strain HRAB-85 was completely sequenced and analysed to understand its antibiotic resistance mechanisms. Population analysis and multilocus sequence typing were performed.ResultsSubpopulations grew in the presence of imipenem at concentrations of up to 64 μg/mL, and the strain was found to belong to ST208. The total length of strain HRAB-85 was 4,098,585 bp with a GC content of 39.98%. The genome harboured at least four insertion sequences: the common ISAba1, ISAba22, ISAba24, and newly reported ISAba26. Additionally, 19 antibiotic-resistance genes against eight classes of antimicrobial agents were found, and 11 genomic islands (GIs) were identified. Among them, GI3, GI10, and GI11 contained many ISs and antibiotic-resistance determinants.ConclusionsThe existence of imipenem heteroresistant phenotypes in A. baumannii was substantiated in this hospital, and imipenem pressure, which could induce imipenem-heteroresistant subpopulations, may select for highly resistant strains. The complete genome sequencing and bioinformatics analysis of HRAB-85 could improve our understanding of the epidemiology and resistance mechanisms of carbapenem-heteroresistant A. baumannii.