Antimicrobial resistance patterns and molecular characterization of Acinetobacter baumannii isolates in non-COVID-19 patients admitted to intensive care units during the pandemic: a retrospective study at a tertiary hospital in Tehran, Iran.

BACKGROUND: Acinetobacter baumannii is one of the most common causes of healthcare-acquired infections, particularly among the critically ill patients in intensive care units (ICUs). Its multidrug-resistance (MDR) nature is a major factor contributing to treatment difficulties, and ultimately increased patient mortality. This study aimed to investigate the prevalence, antimicrobial resistance patterns, and molecular characteristics of A. baumannii strains isolated from ICU patients (non-COVID-19) in Tehran, Iran. RESULTS: The infection rate of A. baumannii among ICU patients was 2.25% (75/3340). More than 90% of isolates showed resistance to key antibiotics including imipenem, meropenem, cefotaxime, and ciprofloxacin. Colistin was the most effective drug, with a susceptibility rate of 61.3%. The majority of the isolates (92%) were categorized as extensively drug-resistant (XDR) and harbored multiple antibiotic resistance genes (ARGs). Among carbapenem resistance genes, blaOXA-23-like was the most prevalent, detected in 72% (54/75) of isolates, followed by blaOXA-24-like in 49.3% (37/75). Regarding aminoglycoside resistance, the genes aac(6')-Ib and ant(2')-Ia were identified in 66.6% (50/75) and 32% (24/75) of the isolates, respectively. Genotyping by multiplex PCR revealed that most of isolates (85.3%) belonged to GC2. Furthermore, REP-PCR genotyping identified eight different genotypes, with one dominant genotype accounting for 81% (51/63) of isolates. CONCLUSION: The present study demonstrates the predominance of XDR A. baumannii strains carrying diverse ARGs in our ICU setting. These findings raise concern, as such strains complicate treatment, limit therapeutic options, and may contribute to poor outcomes in critically ill patients. Mortality was high and appeared more associated with extensive resistance than with comorbidities. The clonal dissemination of these strains further emphasizes the need for robust infection control measures. Implementation of strict infection control measures and robust antibiotic stewardship programs remains essential to limit the spread of these highly resistant pathogens.