Antimicrobial resistant Salmonella spp. circulating in antibiotic-free organic pig farms of northern-Thailand

We investigated the prevalence of Salmonella circulating in local organic pig farms in northern Thailand and typed isolated clones to better understand the population structure of the underlying Salmonella contamination. In total, 112 samples from 11 organic pig farms were processed from October to December 2018. Salmonella were detected in 9 farms with an overall prevalence of 25.0% (28/112). Prevalence detected in fecal, feeder, and boot swab samples was found to be 32.7% (17/53), 17.7% (6/34), and 20.0% (5/25), respectively. Of the 28 positive strains, Seven Salmonella serotypes were identified, with S. Rissen being the most common (15/28; 53.6%). 89.3% (25/28), 78.6% (22/28) and 71.4% (20/28) of isolated Salmonella were resisted against tetracycline, ampicillin, and sulfamethoxazole-trimethoprim, respectively. From multilocus sequence typing (MLST) analysis, the phylogenetic tree suggests dissemination of specific clones within herds that share routes of pig transportation and point mutations in housekeeping genes within herds. A minimum spanning tree (MST) revealed that Salmonella contamination in organic pig farming is possibly linked with conventional farming. Based on the own results, strictly highly organic practices provide a safe alternative enhancing domestic consumer trust and improve public health safety.