Serotype Distribution and Antimicrobial Resistance of Salmonella Isolates in Human, Chicken, and Cattle in Iran

Salmonellais a foodborne zoonotic enteric bacterium able to infect both humans and animals. This study aimed to identify the antimicrobial resistance of Salmonella serovars isolated from human, cattle, and poultry. Moreover, we investigated the probable transmission trends of antibiotic-resistant Salmonella isolates from food animals to human. A total of 242 Salmonella isolates collected from various human and animal sources were serotyped. The polymerase chain reaction was performed to detect the invA virulence gene. The isolates were subsequently tested against 14 antimicrobials and the resistance rates among the isolates from three sample sources were statistically analyzed by the Chi-Square test. Serotyping revealed the isolates belonged to various serovars with the dominance of Enteritidis (37%), Typhimurium (35.3%), and Infantis (21.1%). A high frequency of resistance to streptomycin was observed followed by tetracycline, trimethoprim, sulfonamides, spectinomycin, chloramphenicol, florfenicol, ampicillin, kanamycin, ceftazidime, and cefepime. In addition, multidrug resistance was observed in more than 40% of the isolates. The results of the statistical analysis showed a significant relationship (P ˂ 0.001) between the rate of antibiotic resistance among the three sources of Salmonellaisolates. Furthermore, the antibiotic resistance had a statistical relationship between the different serotypes isolated from different sources. These findings demonstrate the possible transmission of resistance to human from animal sources. The prevalence of the Typhimurium, Enteritidis, and Infantis serovars in both human and animals suggested that Salmonella contamination in chicken and cattle may be the major source of salmonellosis in human. The high incidence of antibiotic resistance in Salmonellaisolates along with the close relationship between the antimicrobial resistance of animal and human isolates indicate the role of food animal products as an important source of resistance.