Genetic Characterization of Plasmid-Borne blaOXA-58 and blaOXA-72 in Acinetobacter pittii in Shaanxi, China

Abstract

BackgroundAcinetobacter pittii has emerged as an opportunistic nosocomial pathogen associated with hospital-acquired infections. The purpose of this study was to investigate the genetic structures of plasmids carrying carbapenemase genes blaOXA-58 and blaOXA-72 in A. pittii strains AR3676 and AR3651 isolated from patients. MethodsAntimicrobial susceptibility testing was performed using broth microdilution. Whole-genome sequencing and bioinformatics analysis were performed to characterize the genome of A. pittii AR3676 and AR3651. Conjugation experiments were conducted to evaluate plasmids transferability. Phylogenetic and comparative genomic analysis were performed to explore the characteristics of carbapenem-resistant A. pittii isolates worldwide. ResultsThe AR3676 strain exhibited resistance to imipenem. The 19,700-bp plasmid pAR3676-OXA-58 harbored blaOXA-58 with genetic contexts consisting of a truncated ISAba3-like-blaOXA58-ISAba3. Additionally, the AR3651 strain exhibited resistance to imipenem and meropenem. The genome of AR3651 comprised one 9,837-bp RepA_AB plasmid pAR3651-OXA-72 harboring blaOXA-72. The blaOXA-72 was flanked by XerC/XerD recombination sites. The conjugation of plasmids pAR3676-OXA-58 and pAR3651-OXA-72 from A. pittii to A. baumannii ATCC 17978RIFR failed three independent times. Phylogenetic analysis of A. pittii strains AR3676, AR3651 and other 504 A. pittii strains collected between 1966 and 2022 from various geographic localities, revealed genetic diversity with a heterogeneous distribution of carbapenemase genes. ConclusionA. pittii strains with plasmid carrying blaOXA-58 or blaOXA-72 may serve as an important reservoir of carbepenemase genes. The carbepenemase genes on a single plasmid may facilitate their dissemination and persistence. Additionally, the pdif sites and mobile elements play an important role in the mobilization of resistance genes and plasmid evolution.