Background and objectives: bla _SHV, bla _TEM and bla _VEB are a group of Extended-Spectrum Beta-Lactamase enzymes (ESBLs) which are able to hydrolyze Penicillins and some cephalosporin antibiotics. The present study evaluated the frequency of ESBL genes bla _SHV, bla _TEM and bla _VEB in Acinetobacter baumannii strains isolated from nosocomial infections to outline the importance of these genes in antibiotic resistance. Methods: One hundred Acinetobacter baumannii strains were isolated from different nosocomial infections. After antibiotic resistance evaluation with the Kirby-Bauer disc-diffusion method, the Minimum Inhibitory Concentration (MIC) of Ciprofloxacin was measured using the E-test method. Then, the ESBL producing strains were identified employing Combined Disk Methods. Finally, all isolates were evaluated with the Polymerase Chain Reaction (PCR) technique to detect the ESBL genes of interest. Results: Out of 100 Acinetobacter baumannii isolates, 59% were ESBL positive according to the phenotypic method. The PCR assay could not detect the bla _SHV and bla _VEB genes in the studied isolates, but the presence of bla _TEM gene was demonstrated in 42% of the strains. Conclusion: The high resistance to most antibiotics, the high prevalence of ESBLs-producing strains and also a high prevalence of bla _TEM gene in A. baumannii strains found in the current study gives cause for major concern about nosocomial infections in Iran because of the treatment complexity of these strains. Our results highlight the need for infection control measures to prevent the spread of resistant isolates, especially in hospitals.

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