The poultry industry in Iran is the main supplier of protein in the food chain. In the present study, we showed the importance of the possible dissemination of clonally related multiple drug resistant (MDR) Salmonella Infantis in broiler farms in Iran. In total, 156 fecal samples belonging to 23 poultry farms in Razavi Khorasan province, northeast of Iran, were examined for the presence of Salmonella serovars. Molecular serotypes and serogroups, class 1 and 2 integron types, colistin resistance genes (mcr-1 and mcr-2) and antimicrobial susceptibility patterns were determined on the recovered Salmonella isolates. Based on PCR analysis, 30 recovered Salmonella isolates were identified as S. Infantis (23 isolates; 76.6%), S. Enteritidis (six isolates; 20%), and one isolate (3.3%) was not serotyped by the applied method. Class 1 integrons were detected in 22 isolates (95.6%) and class 2 integrons were not detected in any of the isolates. Although colistin resistance was prevalent in disc diffusion test, mcr-1 and mcr-2 genes were not detected. All class 1 integrons carried the cassette aadA1 gene. All Salmonella isolates were resistant to colistin and amoxicillin/clavulanic acid and MDR patterns were observed in most (96.6%) isolates. This study revealed a high prevalence rate of S. Infantis and the presence of class 1 integrons in broiler farms. The presence of the same integron cassettes in the sequenced isolates suggests that strains are clonally related. Stringent monitoring programs are required to prevent the spreading of MDR Salmonella serovars into food chain via poultry products.

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