Carbapenem-hydrolyzing oxacillinases are reported increasingly in Acinetobacter baumannii. Here we report the contribution of carbapenem-hydrolyzing oxacillinases genes to carbapenem resistance in clinical Acinetobacter baumannii strains in Saudi Arabia. Forty non-repetitive clinical A. baumannii strains were isolated and identified from 40 patients, hospitalized in various wards in King Khalid University and Armed Forces Hospitals (Riyadh, Saudi Arabia). Antibiotic susceptibility testing

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... ted that most isolates (65 to 100% of the total strains) were resistant to -lactams antibiotics with minimum inhibitory concentrations (MICs) ranged from low to very high values. In addition, 65 and 67.5% of the total isolated clinical strains were resistant to carbapenem antibiotics, including imipenem and meropenem, respectively. Based on antibiotic susceptibility, it was possible to divide the isolated clinical A. baumannii strains into four phenotypes clusters, I, II, III and IV, with multiple antibiotic resistance of > 90% (with very high MICs), 80 to 89% (with high MICs), 70 to 79% (with moderate MICs), and 40 to 69 (with moderate to low MICs), of the total antibiotics (n = 17), respectively. The results of polymerase chain reaction (PCR) products analysis reveals that the major groups of oxacillinases genes including bla OXA-23 , bla OXA-24 , and bla OXA-58 were detected in 72.5% (n = 29), 45% (n = 18) and 37.5% (n = 15) of the isolated A. baumannii strains, respectively. In addition, analysis of the prevalence of different oxacillinases genes in different antibiotics-based phenotypes clusters, revealed that cluster I harbored the highest distribution of resistant genes, which could explain the extremely multiple antibiotic resistance phenotype within the strains of this cluster.