Genotyping, Phage Typing, and Antimicrobial Resistance of Salmonella Typhimurium Isolated from Pigs, Cattle, and Humans

Abstract

Salmonella enterica serovar Typhimurium (ST) is one of the most common serovars isolated from humans and animals. It has been suggested that ST infections in Koreans are largely due to the consumption of contaminated pork and beef. To investigate the genotypes, phage types, and antimicrobial resistance patterns for ST isolates of different origins, a total of 70 ST strains, including 19 isolates from humans, 44 isolates from pigs, and 6 isolates from cattle, were analyzed using pulsedfield gel electrophoresis (PFGE), phage typing, and antimicrobial susceptibility tests. Forty-three distinct PFGE patterns were generated from 70 ST isolates, which were grouped into 14 PFGE groups (from A to N) at the level of 75% similarity. The most prevalent group was the A (A1-A17 subtypes) group, encompassing 54.5% (38/70) of ST isolates. ST isolates from pigs and cattle mostly belong to groups A and L, whereas ST isolates from humans mostly belong to groups F and C. Antimicrobial susceptibility tests using 11 antimicrobial agents showed that resistance to tetracycline (TE) (81.4%) was highly prevalent, followed by streptomycin (S) (64.3%) and nalidixic acid (NA) (31.4%) resistance. A total of seventeen antimicrobial resistance patterns were observed. Only 8.6% of isolates, including a reference strain, were susceptible to all antimicrobial agents tested. The most prevalent resistance pattern was TE-S (37.1%), which was seen in 66.6% of bovine, 40.8% of swine and 21.1% of human isolates. Three ST isolates from humans (15.9%) showed resistance to 7-8 antimicrobials. The most predominant phage type (PT) was U302 (64.3%), followed by DT170 (10.0%). PFGE types did not coincide with antimicrobial resistance patterns and phage types; therefore, the combination of those types allowed for further differentiation between tested ST isolates.

Genomic Approaches for Understanding the Characteristics of Salmonella enterica subsp. enterica Serovar Typhimurium ST1120, Isolated from Swine Feces in Korea

“…S. Typhimurium ST1120 was isolated from feces of pigs [13]. This ST1120 strain was cultivated in Luria-Bertani (LB) broth at 37°C for 3 h with constant shaking at 220 rpm until it reached log phase.…”

“…S. Typhimurium strain ST1120 (also called HID1120) was first isolated from feces of pigs in Gangwon Province, Korea [13]. Its whole genome was fully sequenced and analyzed in this study.…”

Prevalence of Salmonella spp. and Escherichia coli in the feces of free-roaming wildlife throughout South Korea

“…Irrigation water contaminated with feces is often responsible for the pathogen contamination of leafy greens [ 25 , 26 ]. Salmonella was detected in the feces of various animals, including wild boar [ 27 , 28 ], wild foxes, ducks [ 29 ], stray dogs, coyotes [ 30 ], hedgehogs [ 31 ], tigers [ 32 ], cattle [ 33 ], magpies [ 31 ], and waterfowls [ 34 ]. Owing to their omnivorous feeding habits, wild animals are major reservoirs of Salmonella and can be exposed to Salmonella colonization through fecal shedding [ 31 ].…”

“…Animals such as cattle and pigs must be treated with precaution because they are considered a most frequent sources of salmonellosis outbreaks in humans in Korea [27,36,42]. Ultimately, the cross-contamination of fresh fruits and vegetables is caused by different pathogenic agents, including Salmonella and E. coli in Korea [43].…”