Determination of serogroup and antibiotic resistance pattern of Salmonellas isolated from commercial laying poultry of Tabriz area

Salmonellosis is one of the most important zoonotic diseases. Using a variety of antibiotics is the key to reducing the incidence and mortality associated with Salmonella infections. However, incorrect use of antibiotics in commercial poultry farms may lead to the emergence of antibiotic resistance and consequently inadequate antimicrobial drugs. Also, the transfer of antibiotic-resistant strains to humans through the food chain could also be a public health threat. Therefore, the aim of this study was to determine the serogroup and antibiotic resistance pattern in Salmonella isolates from 8 commercial laying herds in Tabriz area. For this purpose, after isolation of Salmonella from different samples, the isolates were tested by specific antisera and then their antibiotic resistance pattern was determined using disk diffusion method (based on Kirby-Bauer method) against the 6 types of antibiotics used in the poultry industry in Iran (Enrofloxacin, Fluorphenicol, Fosphomycin, Lincospectin, Soltream and Doxycycline) and 6 types of antibiotics used  in humans (Gentamicin, Co-amoxiclav, Ciprofloxacin, Cefalexin, Cefotaxime and Ceftriaxone). From the 96 tested samples, 16 isolates of Salmonella were identified with 10 isolates belonging to serogroup D but 6 isolates did not belong to any of the tested serogroups. Also, all isolates were sensitive to Gentamycin and Fosfomycin and the highest resistance was observed towards Doxycycline with an abundance of 83.35%. The relatively high prevalence of drug resistance among Salmonella isolates from commercial laying poultry showed that antibiotics should be administered with more caution and care.