Genomic characteristics of the multiresistant Acinetobacter baumannii global clone 1 reference strain A297/RUH875

Acinetobacter baumannii ST1, also known as global clone 1 (GC1), is a globally distributed lineage associated with antimicrobial resistance (AMR). The multiresistant isolate A297/RUH8751, recovered from a urinary tract infection in the Netherlands in 1984, has served as a reference strain for ST1. We aimed to generate and analyse the complete genome sequence of A297/RUH8751 to provide insights into its genomic features, antibiotic resistance determinants and phylogenetic placement.

WGS was performed using Oxford Nanopore GridION and Illumina HiSeq platforms. Assembly was conducted with Autocycler v0.2.1. Genomic features, including antibiotic resistance genes, insertion sequences and restriction-modification systems, were characterized using ResFinder, ISFinder and REBASE. Comparative analyses were conducted with the draft genome of NIPH 527, which also represents RUH875, to assess sequence variations. Phylogenetic analysis was performed to determine the evolutionary placement of A297/RUH875 within GC1.

The complete genome of RUH875 (A297) consists of a 3 965 450 bp chromosome and three plasmids: pA297-1 (pRAY*; 6078 bp), pA297-2 (8731 bp) and pA297-3 (a 200 kb conjugative plasmid). The chromosome harbours the AbaR21 genomic resistance island, carrying seven antibiotic resistance genes and six prophage regions. Notably, bap1 and bap2, biofilm-associated genes, were fully resolved, with bap1 identical to that of A. baumannii A1-the earliest GC1 isolate. Comparative analysis with A1 revealed 122 SNPs, with clustered variations suggesting potential recombination events. Phylogenetic analysis confirmed A297/RUH875 as a distinct lineage within GC1. The completed genome sequence provides a reference, in addition to strain A1, for studying AMR evolution in GC1 and enhances comparative genomic analyses.