Isolation, Molecular Identification, and Antibiotic Resistance Profile of Salmonella Typhimurium Isolated from Calves Fecal Samples of Dairy Farms in Hamedan

Introduction: Calf diarrhea is one of the significant problems in dairy farms associated with treatment costs and reduced livestock production. Salmonellae are among the most common and the major causative agents of diarrhea in calves and humans. The present study was carried out to isolate and identify Salmonella in fecal samples of calves in industrial dairy farms of Hamedan and to determine antibiotic resistance profiles of the probable isolates. Methods: Salmonella were presumptively isolated based on the cultural characteristics and biochemical tests, and the identity of the isolates was further confirmed using genus- and serotype-specific PCR assays. Kirby-Bauer disk diffusion method was performed to determine antibiotic resistance profiles of the isolates. Results: Out of 120 stool samples collected from 8 industrial farms, 22 (18.33%) isolates possessing rfbJ, fliC and fljB genes were identified as Salmonella Typhimurium serotype. Antibiotic susceptibility test revealed all isolates (100%) were susceptible to gentamicin, amoxicillin-clavulanic acid, kanamycin, and ciprofloxacin and resistant against cotrimoxazole, cefazolin, and cefixime. Conclusion: To our knowledge, this study was the first report of Salmonella infection in Hamedan's dairy farms, indicating a relatively high prevalence rate of S. Typhimurium infection as the only detected serotype. Antibiotic resistance should also be considered a severe public health concern. Thus, effective hygiene measures should be adopted to prevent or reduce the infection, and monitoring antibiotic susceptibility is required to choose the drug of choice for treatment.