Characterization of antibiotic resistant patterns of Salmonella serotypes isolated from beef and chicken samples in Tehran

Introduction and Infection with Salmonella is the most frequently reported cause of bacterial food-borne illness worldwide. Raw meat samples are a common source and, in recent years, much attention has been focused in determining the prevalence of Salmonella during the different stages in the poultry and beef production chain. This study was conducted to examine the prevalence of Salmonella contamination, and the antibiotic resistance characteristics of isolated strains, from raw samples of packed and unpacked beef and chicken collected randomly from retail stores in Tehran. A total of one hundred and thirty three samples were collected from 27 meat providing retail stores in Tehran. Salmonella strains were isolated and identified according to the techniques recommended by the International Organization for Standardization (ISO 6579, 1998). Antimicrobial resistance test was performed by disk diffusion method using 13 antibiotics. Out of one hundred and thirty three samples tested, fifty one (38.3%) were identified as Salmonella strains. The percentages of Salmonella in chicken and beef samples were 62.7% and 37.3% respectively. The sereotyping results showed that isolated strains belonged to 10 different serotypes, and the most dominated serotype was Salmonella thompson (54.9%). Among the variety of antibiotics tested, the highest resistance was found with nalidixic acid followed by tetracycline, trimethoprim, and streptomycin. The percentages resistance of isolates from chicken samples to nalidixic acid, tetracycline, trimethoprim, and streptomycin were 90.6%, 71.9%, 56.6%, and 25%, and the isolates from meat samples were 36.8%, 21%, 26.3%, and 5.3% respectively. About 23.5% of theSalmonella strains were multiresistant to two or more antibiotic families. Finally, six resistance profiles have been identified. In overall, the degree of resistance of serotypes to nalidixic acid was greater than other tested antibiotics. Our results indicate that antimicrobial resistant Salmonella strains were widely spread among raw chicken and beef meats samples.