Molecular identification of Salmonella Infantis isolated from backyard chickens and detection of their resistance genes by PCR

This study aims at molecular identification of Salmonella Infantis isolated from backyard chickens and the detection of their antibiotic resistance genes. A total of 46 Salmonella-suspected samples isolated from backyard chickens of northern Iran were collected. Serotyping was done by the traditional method and then confirmed by PCR. Antimicrobial susceptibility of the isolates against 13 antimicrobial agents was determined by the standard disk diffusion method. There were 44 samples identified as Salmonella. Serotyping results showed that all 44 isolates belonged to serogroup C1 and serovar Infantis. The most resistance observed was to tetracycline and doxycycline (100%), chloramphenicol (79%) and florfenicol (72%). The floR, catI, tetA and tetG genes were used for the detection of florfenicol chloramphenicol and tetracycline resistance. In order to identify the phenotypic resistance in strains which showed resistance genes by PCR, colony PCR and culture on plates each containing antibiotic was performed simultaneously. All the Salmonella Infantis resistant to florfenicol and chloramphenicol harbored floR and catI. None of the Salmonella resistant to tetracycline carried tetA or tetG. The result of colony PCR and culture in antibiotic medium confirmed theresults of PCR and indicated phenotypic resistance in these samples.