Molecular epidemiology and antimicrobial resistance of Salmonella isolates from broilers and pigs in Thailand

Aim: This study aimed to determine the prevalence and antimicrobial resistance pattern of Salmonella spp., and the genetic relatedness between isolates from broilers and pigs at slaughterhouses in Thailand. Materials and Methods: Fecal samples (604 broilers and 562 pigs) were collected from slaughterhouses from April to July 2018. Salmonella spp. were isolated and identified according to the ISO 6579:2002. Salmonella-positive isolates were identified using serotyping and challenged with nine antimicrobial agents: Amoxicillin/clavulanate (AMC, 30 μg), ampicillin (AMP, 10 μg), ceftazidime (30 μg), chloramphenicol (30 μg), ciprofloxacin (CIP, 5 μg), nalidixic acid (NAL, 30 μg), norfloxacin (10 μg), trimethoprim/sulfamethoxazole (SXT, 25 μg), and tetracycline (TET, 30 μg). Isolates of the predominant serovar Salmonella Typhimurium were examined for genetic relatedness using pulsed-field gel electrophoresis (PFGE). Results: Salmonella was detected in 18.05% of broiler isolates and 37.54% of pig isolates. The most common serovars were Kentucky, Give, and Typhimurium in broilers and Rissen, Typhimurium, and Weltevreden in pigs. Among broilers, isolates were most commonly resistant to antibiotics, NAL, AMP, TET, AMC, and CIP. Pig isolates most commonly exhibited antimicrobial resistance against AMP, TET, and SXT. Based on PFGE results among 52 S. Typhimurium isolates from broilers and pigs, a high genetic relatedness between broiler and pig isolates (85% similarity) in Cluster A and C from PFGE result was identified. Conclusion: The results revealed high cross-contamination between these two animal species across various provinces in Thailand