Molecular analysis of clinical <i>Acinetobacter baumannii</i> isolates based on colistin resistance, biofilm formation, clonal relationships, and <i>pmr</i> A gene expression

Aims This study investigates the molecular characteristics of multidrug-resistant Acinetobacter baumannii (MDRAB) clinical isolates with particular emphasis on colistin resistance, biofilm formation, antimicrobial resistance determinants, clonal relatedness, and pmrA gene expression.Methods Twenty MDRAB isolates were collected from intensive care unit patients at Afzalipour Hospital, Kerman, Iran. Antimicrobial susceptibility testing was performed using the broth microdilution method according to the EUCAST 2022 guidelines. Polymerase chain reaction (PCR) was used to detect extended-spectrum β-lactamase (ESBL), carbapenemase, biofilm-associated genes, and class 1 integrons. Clonal relatedness was assessed using Repetitive-element PCR (Rep-PCR), and the pmrA gene (GenBank accession no. MN787072.1) expression analyzed through quantitative RT-PCR (qRT-PCR).Results The isolates demonstrated high minimum inhibitory concentrations (MICs) particularly against carbapenems. Many isolates showed strong biofilm, while carrying biofilm-associated genes bap, csuE, pgaA, and ompA. Class 1 integrons and the blaCTX-M gene detected in 94% and 65% of isolates, respectively. Colistin-resistant (ColR) isolates shared a distinct Rep-PCR profile (singleton) and harbored both the pmrA and blaCTX-M-15 genes. DNA sequencing and qRT-PCR analysis revealed that, the Q218→K mutation had marginal effect on pmrA gene expression.Conclusion These findings underscore the urgent need for effective antibiotic stewardship to address rising incidence of carbapenemase-producing, colistin resistance in A. baumannii.