Molecular Epidemiology and Genetic Profile of Non-Typhoidal Salmonella Serovars Isolated From Poultry Production Chain in Khorasan Province, Iran: A Comprehensive Analysis of Prevalence, Virulence Genes, and Antibiotic Resistance.

Non-typhoidal Salmonella (NTS) serovars are important foodborne zoonotic pathogens that threaten human health and contribute to the evolution and global dissemination of antibiotic resistance. This study investigated the virulence characteristics, antibiotic susceptibility, serovar distribution, and antimicrobial resistance determinants of 132 NTS isolates obtained from the poultry production chain in Khorasan Province, Iran, between 2018 and 2020. Salmonella Infantis was the predominant serovar, accounting for 53.8% of isolates, followed by S. Enteritidis (20.5%), S. Typhimurium (3.8%), and 22% of isolates could not be typed by multiplex PCR and were categorized as non-typed Salmonella. Based on antibiotic susceptibility tests, most Salmonella isolates exhibited high resistance to tiamulin (97%), flumequine (81.1%), ampicillin (96.2%), and streptomycin (78.8%). A total of 65 multidrug-resistant (MDR) profiles were identified. Conversely, gentamicin (97%), ciprofloxacin (94%), enrofloxacin (90.9%), cefotaxime (89.4%), and colistin (88.6%) demonstrated the greatest effectiveness against these NTS isolates. The most frequently identified antimicrobial resistance genes (ARGs) were blaTEM (91.7%), sul1 (80.3%), and aadA (78.8%). In addition, PCR analysis of virulence genes showed that all isolates harbored the stn and iroN virulence genes. However, pefA and the Salmonella plasmid virulence genes (spvB, spvC, and spvR) were detected in 53% and 36.4% of the isolates, respectively. In conclusion, our findings highlight the increasing prevalence of MDR S. Infantis, which has replaced S. Enteritidis and S. Typhimurium as the dominant serovars in the poultry production chain. Effective control of NTS in poultry production chain requires regular monitoring and surveillance of NTS infections, serotype diversity, and antimicrobial resistance profiles.