Virulent Genes and Genetic Relationship of Salmonella spp. Isolated from Chickens and Husbandry Environments in Small-Scale Farms in the Mekong Delta, Vietnam

Salmonella is one of the most severe pathogens causing diseases in poultry and humans, and several factors could become transmission vectors in the husbandry environment. This study was conducted from April to July 2024 to clarify the prevalence of common Salmonella serovars in chickens and the husbandry environment and their pathogenicity and genetic relationship in small-scale farms in the Mekong Delta, Vietnam. A total of 279 samples were randomly collected from fresh chickens’ feces (n = 54), husbandry environment (n=81), and pests (n=144), including rats, geckos, and ants, in four small-scale farms to examine the prevalence of Salmonella spp. By the conventional isolation method, 75 samples were positive for Salmonella, accounting for 26.88%. The prevalence of Salmonella in chicken feces, the environment, and pests were 27.78%, 12.35%, and 34.72%, respectively. Of 75 positive Salmonella isolates, two common serovars were identified, including S. Gallinarum (13.33%) and S. Enteritidis (10.67%); however, S. Pullorum and S. Typhimurium were not detected using PCR. These Salmonella isolates were detected virulent genes by using PCR, and found that these isolates harbored several virulent genes, including InvA (100%), fimA (100%), stn (93.33%), sopB (89.33%), and sodC1 (54.57%). The ERIC-PCR method was used to determine the genetic relationship among Salmonella strains carrying virulent genes present in chickens, environment, and pests in these small-scale farms. The results showed diversity in phenotype and similarity in the genetic relationship (more than 75% similarity) among Salmonella strains isolated from chicken feces and the livestock environment. In conclusion, the study indicated that pathogenic Salmonella serovars could survive and be transmitted among sources, including chickens, the husbandry environment, and pests in small-scale poultry farms in the Mekong Delta.