Genomic analysis of early ST32 Acinetobacter baumannii strains recovered in US military treatment facilities reveals distinct lineages and links to the origins of the Tn6168 ampC transposon

Liam A Tobin; Eradah Abu Sabah; Francois Lebreton; Garry S A Myers; Patrick T McGann; Mehrad Hamidian

doi:10.1093/jac/dkae454

Genomic analysis of early ST32 Acinetobacter baumannii strains recovered in US military treatment facilities reveals distinct lineages and links to the origins of the Tn6168 ampC transposon

J Antimicrob Chemother. 2024 Dec 16:dkae454. doi: 10.1093/jac/dkae454. Online ahead of print.

Authors

Liam A Tobin¹, Eradah Abu Sabah¹, Francois Lebreton², Garry S A Myers¹, Patrick T McGann², Mehrad Hamidian¹

Affiliations

¹ Australian Institute for Microbiology and Infection, University of Technology Sydney, Ultimo, NSW 2007, Australia.
² Multidrug Resistant Organism Repository and Surveillance Network, Walter Reed Army Institute of Research, Silver Spring, MD, USA.

PMID: 39680383
DOI: 10.1093/jac/dkae454

Abstract

Objectives: To study the population structure and genomic characteristics, including antimicrobial resistance genes, plasmid types and surface polysaccharide type, of the globally distributed Acinetobacter baumannii belonging to ST32 (Institut Pasteur scheme).

Methods: Antibiotic resistance phenotype for 19 antibiotics was determined using Vitek 2. Whole-genome sequencing was performed using the Illumina MiSeq platform. Genomes were assembled using Newbler. Phylogenetic analysis was done by determining the core-genome alignments using Panaroo v1.3, analysed in IQ-Tree2 v2.2.0.3 to construct Maximum Likelihood trees using the RaxML software. Resistance genes and IS were identified using the Abricate programme, and ISFinder databases.

Results: One hundred and thirty-three (n = 133) ST32 A. baumannii isolates were analysed in this study. These genomes originated mainly from US military treatment facilities (n = 113), but also included additional publicly available genomes in GenBank (n = 20) recovered from a broad geographic distribution extending to Asia and South America. Phylogenetic analysis of all 133 genomes revealed at least four clades, with over 80 genomes forming a tightly clustered branch, suggesting they are likely to represent outbreak strains. Analysis of the ampC region showed that ST32 strains played a significant role in the formation of the widely distributed ampC transposon, Tn6168, and supplying DNA segments containing an ISAba1-ampC from ST32s via homologous recombination.

Conclusions: ST32 strains played a significant role in the evolution of antibiotic resistance in several widely distributed sequence types including ST1 (global clone 1) and ST3.

Abstract

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