Genotypic and Phenotypic Characterization of Salmonella Typhimurium Strains Isolated from Swine in the Southern Region of Brazil

Salmonella Typhimurium has long been one of the most frequently isolated serovars in animal and human infections. Pork has been involved in the dissemination of S. Typhimurium to humans and plays an important role in the epidemiology of this infection. This study aimed to characterize genotypically and phenotypically S. Typhimurium strains isolated from swine in Brazil. The genomic relatedness among 17 of the 18 S. Typhimurium genomes was ≥ 90% according to Gegenees analysis, while ANI analysis showed ≥ 98.2% similarity across all 18 genomes, with most strains belonging to SNP cluster PDS000201117.2. Virulence factors and stress-related genes were searched at NCBI Pathogen Detection. All strains carried the iroB, iroC, sinH, asr, golS, and golT genes. Under acid stress, all strains survived after 10 min and 1 h. Under oxidative stress, 17 (94.44%) strains survived after 10 min, and 11 (61.11%) strains survived after 1 h. The invasion rates in Caco-2 cells ranged from 37.50% to 100%, and survival in the macrophage assay ranged from 37.50% to 87.50%. In conclusion, the close genetic relationship observed among the S. Typhimurium strains isolated from swine studied may suggest that a predominant subtype may have prevailed in Brazil's swine sources. The high prevalence of some heavy metal tolerance encoding genes is alarming due to their potential to influence in the co-selection of S. Typhimurium strains resistant to antibiotics. Moreover, the presence of some virulence genes and the notable stress survival and cell invasion capacities highlighted the importance of surveillance to prevent the dissemination through food of virulent S. Typhimurium strains present in livestock to humans.