Tarbiat Modares University Infection Epidemiology and Microbiology 2588-4107 12 1 2026 02 01 Molecular Epidemiology of Acinetobacter baumannii Isolates Using Single-Locus Sequence Typing of blaOXA-51-like and ampC Genes as a Cost-Effective Method 53 60 28720 10.66224/iem.12.1.53 EN Farzaneh Firoozeh Department of Microbiology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran. Evidence-based Phytotherapy and Complementary Medicine Research Center, Alborz University of Medical Sciences, Karaj, Iran. 0000-0002-4026-4110 Zahra Hoseini Department of Microbiology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran Mohammad Mohammadzadeh Department of Microbiology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran. 0000-0001-8526-4504 Farzad Badmasti Department of Bacteriology, Pasteur Institute of Iran, Tehran, Iran 0000-0003-3502-147X Mohammad Zibaei Department of Parasitology and Mycology, School of Medicine, Alborz University of Medical Sciences, Karaj, Iran Center for Research of Endemic Parasites of Iran, Tehran University of medical Sciences, Tehran, Iran 0000-0003-2265-7460 Sepeta Zibaei Student Research Committee, Alborz University of Medical Sciences, Karaj, Iran 0009-0006-3630-0314 Journal Article 2025 09 27 <strong>Background:</strong> Acinetobacter baumannii is a crisis-causing opportunistic pathogen with a high capacity for clonal spread. blaOXA-51-like and ampC sequence-based typing (SBT) is a cost-effective and reliable technique to identify global and widespread lineages of A. baumannii strains. This research aimed to study circulating A. baumannii clones using single-locus sequence typing (SLST) as a reliable and cost-effective method.<br><strong>Materials & Methods:</strong> A total of 119 A. baumannii clinical isolates were collected from hospital inpatients from February to September 2024. The antibiotic resistance profile of A. baumannii isolates was determined, and genotyping was performed using SBT of blaOXA-51-like and ampC genes.<br><strong>Findings:</strong> All A. baumannii isolates were specified as multidrug-resistant (MDR), and 78.1% were identified as carbapenem resistant. Resistance to colistin was observed in 5% of isolates with a minimum inhibitory concentration (MIC) of ≥128 μg/mL. SBT of the blaOXA-51-like gene revealed four various blaOXA-51-like allele variants: including blaOXA-69 (n=47, 39.5%), blaOXA-64 (n=21, 17.6%), blaOXA-383 (n=44, 37%), and blaOXA-441 (n=7, 5.9%). SBT of the ampC specified two alleles, including ampC-1 (n=47, 39.5%) and ampC-25 (n=21, 17.6%), and 51 (42.9%) isolates showed an undetermined allele variant of the ampC gene. blaOXA-69 /ampC-1 and blaOXA-64 / ampC-25 pertained to sequence type 1/ clonal complex 1 (ST1/CC1) and ST25/CC25, respectively. <br><strong>Conclusion:</strong> SBT of the blaOXA-51-like and ampC genes revealed a relatively high prevalence of the international ST1/CC1 clone in MDR A. baumannii isolates in our region. However, the blaOXA-383 allele variant, which could possibly be associated with endemic clones, also had an approximately significant frequency. https://iem.modares.ac.ir/article_28720_7c08f51438fbd3ee4cbb942a0b87eb9e.pdf