Genetic diversity and antimicrobial resistance of clinical Acinetobacter baumannii isolates: insights from ERIC typing.

Acinetobacter baumannii is a major nosocomial pathogen, and multidrug-resistant (MDR) and extensively drug-resistant (XDR) isolates pose a serious threat to healthcare systems worldwide. Genetic diversity among clinical isolates contributes to variable resistance profiles, complicating treatment strategies and infection control efforts. In this study, 102 non-duplicate A. baumannii isolates were collected over 1 year from Shahid Beheshti Hospital, Kashan, Iran, predominantly from bronchoalveolar lavage samples. Antimicrobial susceptibility testing revealed high resistance rates against piperacillin/tazobactam (93.1%), meropenem (93.1%), and ciprofloxacin (91.2%), while tobramycin retained the highest in vitro activity. ERIC-PCR genotyping identified 38 distinct genotypes clustered into five groups, with clusters I-IV representing major lineages. Cluster I exhibited significantly higher resistance to meropenem, tobramycin, gentamicin, and ciprofloxacin compared to other clusters (p < 0.05), and overall, 64.8% of isolates were closely related, indicating clonal dissemination within the hospital. These findings demonstrate the coexistence of multiple XDR lineages and highlight a strong association between clonal types and antimicrobial resistance patterns. Integrating molecular surveillance with antibiotic stewardship and infection control measures is essential to limit the spread of MDR and XDR A. baumannii in healthcare settings.