Evaluation of multi-drug resistance, virulence factors, and antimicrobial resistance genes of non-typhoidal Salmonella isolated from ruminants as a potential human health threat in Razavi Khorasan, northeastern Iran

Non-typhoidal Salmonella (NTS) is a significant foodborne pathogen that poses a threat to human health by causing infections and potentially acquiring antibiotic resistance. We evaluated thirty-five Salmonella serovars previously isolated from cattle, sheep, goats, and their retail meat in Razavi Khorasan Province, Iran. The isolates were confirmed with Salmonella polyvalent antiserum. Furthermore, PCR was used to identify the Salmonella Enteritidis, Salmonella Typhimurium, and the host-adapted serovars Salmonella Dublin and Salmonella Abortusovis. Additionally, the antimicrobial susceptibility of the serovars was evaluated using the disk diffusion method. Subsequently, the occurrence of antimicrobial resistance genes and virulence factors was evaluated using the PCR technique. Molecular typing revealed that 20 % of the isolates were S. Typhimurium, 11.4 % were S. Dublin, 8.6 % were S. Enteritidis, 5.7 % were S. Abortusovis, and 54.3 % (19 isolates) were classified as nontyped serovars. Salmonella isolates showed high susceptibility to ciprofloxacin (91.4 %), colistin (88.6 %), gentamicin (88.6 %), and cefotaxime (85.7 %) while exhibiting high resistance to others such as ampicillin (88.6 %), streptomycin (74.3 %), and tetracycline (51.4 %). The most prevalent resistance genes in non-typhoidal Salmonella (NTS) are blaTEM (91.4 %), sul1 (65.7 %), and aadA (54.3 %). Additionally, twenty-five isolates (71.4 %) showed multi-drug resistance profiles. The most frequent virulence genes are stn (100 %), iroN (100 %), and pefA (42.9 %). The current study has revealed that Salmonella serovars isolated from sheep and goats, like those from cattle, exhibit multi-drug resistance and harbor antimicrobial resistance genes. Additionally, they possess diverse virulence factors that can threaten human health by spreading diseases and developing drug resistance, leading to antibiotic treatment failure.