Colistin resistance and resistance determinants are mobile among Salmonella enterica isolates from diseased and healthy pigs in Thailand https://doi.org/10.12982/VIS.2026.082
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Abstract
Salmonella is an important enteric pathogen that poses a threat to human and livestock animal health, with emerging multidrug resistance (MDR) a major public health issue globally. A total of 150 fecal samples were collected from pigs housed from 4 separate pig farms in southern Thailand and tested for the presence of Salmonella. Confirmed Salmonella isolates were tested for their susceptibility to 11 antimicrobials, and PCR used to detect antimicrobial resistance genes (ARGs). Salmonella isolates were cultured from 69% (103/150) of all fecal samples, with higher prevalence in diseased pigs (12/15; 80%), compared with healthy pigs (91/135; 67%). Serotype Rissen was the most frequently identified serotype among the Salmonella isolates. Resistance to ampicillin (AMP) (97%), sulfonamide-trimethoprim (SXT) (97%), and tetracycline (TET) (94%) were the most common phenotypes observed. The most common ARGs identified were blaTEM (99%), tetA (87%), sul1 (77%), and dfrA1 (74%), and more than 95% of the Salmonella isolates tested were MDR - based on resistance to three or more antimicrobial classes. The most common antimicrobial resistance pattern exhibited was AMP-TET-SXT (76%), and resistance to colistin (via the mcr-1 gene) was observed in both healthy and diseased pigs. The clonal groups of PFGE analysis in each serotype revealed the genetic relationship among Salmonella isolated from healthy and diseased pigs from different pig farms. The pulsotype of Salmonella is clonal in both healthy and diseased pigs, providing crucial genetic evidence for the circulation of Salmonella in the area and its potential spread of MDR through the pig production chain.
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