Molecular epidemiology and antimicrobial resistance of Salmonella spp. isolated from broilers and pigs at slaughterhouses in Thailand and China

Abstract

This study aimed to compare the antimicrobial resistance patterns and DNA restriction patterns by PulsedField Gel Electrophoresis (PFGE) between Salmonella spp. isolated from broilers and pigs in Thailand and China. One
hundred and sixty six isolates were collected from broilers and pigs at slaughterhouses in Khon Kaen, Thailand (n=106)
between February to August 2017 and in Chongqing, China (n=60) between March to October 2015. Antimicrobial
susceptibility of the isolates was determined using the disk diffusion method with nine antimicrobial agents. Genotypic
diversity of the isolates used PFGE of Xbal-digested chromosomal DNA to determine. Of 166 Salmonella isolates, 37
serotypes were identified. The Thai isolates were composed of 18 serotypes, of which S. Rissen was most common
(34%). The Chinese isolates consisted of 23 serotypes, of which S. Derby was most common (22%). The antimicrobial
resistance profiles of Salmonella isolates demonstrated that 38% (63/166) of the isolates were multidrug resistance
(MDR), with 20.8% (22/106) of the Thai isolates and 68.3% (41/60) of the Chinese isolates being identified as MDR.
Salmonella Typhimurium and S. Give isolated from Thailand and China were found to be clonally unrelated. It is
noteworthy that a close genetic relationship, at more than 90% similarity, was observed between S. Rissen isolated from
pigs in China and Thailand. Based on these results, better surveillance systems for Salmonella spp. should be
implemented, and the use of antibiotics in food animal production should be more tightly regulated in both Thailand
and China. The monitoring program of Salmonella dissemination should stay vigilant for S. Rissen between Thailand
and China.