Characterization of blaOXA-542-mediated carbapenem resistance in Acinetobacter baumannii

Abstract Background Carbapenem-resistant Acinetobacter baumannii (CRAB) causes multiple anatomical site infections, representing a significant public health threat. Aim This study reports the isolation and characterization of a carbapenem-resistant A. baumannii harbouring blaOXA-542, followed by a comprehensive investigation of its antimicrobial resistance mechanisms and genomic characteristics. Methods Firstly, antimicrobial susceptibility testing was performed using the broth microdilution method. Subsequently, whole-genome sequencing was employed to identify and characterize the resistance and virulence determinants. The functional validation of resistance mechanisms was performed by gene knockdown and construction of expression vectors. The fitness cost of β-lactamase expression was identified by a bacterial growth kinetic test. Molecular docking was utilized to predict potential binding sites of β-lactamase and carbapenems. Finally, the genetic characteristics of the isolates were analysed through comparative genomics analyses and phylogenetic tree construction. Results and conclusions The results demonstrated that blaOXA-542 confers resistance to carbapenem and penicillin in A. baumannii and Escherichia coli while exhibiting no significant impact on cephalosporins. The ability of blaOXA-542 to hydrolyze meropenem was further confirmed by modified carbapenem inactivation assay (mCIM). Expression of blaOXA-542 in E. coli BL21 showed no significant growth rate alteration. Comparative analysis of the blaOXA-542 genetic environment revealed a close association with Acinetobacter pitti. This study reports the emergence of blaOXA-542-mediated carbapenem and penicillin resistance in a novel A. baumannii lineage (ST2795Pas/ST3464Oxf), highlighting the urgent need for rational antibiotic use against specific pathogens.