P-024. PFGE Genotyping and Antimicrobial Resistance of Salmonella Typhimurium Isolated from Pigs, Cattle and Humans in Korea
Salmonella enterica serovar Typhimurium (ST) is one of the most common serovars isolated from humans and animals. It was suggested that ST infections in humans are largely due to the consumption of contaminated pork and beef with ST in Korea. To investigate genotypes and antimicrobial resistance patterns for ST isolates from different origins, a total of 70 ST strains including 19 isolates from humans, 44 isolates from pigs and 6 isolates from cattle were analyzed by pulsed-field gel electrophoresis (PFGE) and antimicrobial susceptibility test. PFGE using XbaI macrodigestion of DNA was performed and data were analyzed by BioNumerics software packages. Forty three distinct PFGE patterns were generated among 70 ST isolates and these grouped into 14 PFGE groups (from A to N) at the level of 75% similarity. The most prevalent group was A (A1-A17 subtypes) group comprising 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 F and C groups. Antimicrobial resistance was most often observed to tetracycline (TE) (81.4%), followed by streptomycin (S) (64.3%) and nalidixic acid (NA) (31.4%) by antimicrobial susceptibility test using 11 antimicrobial agents. Seventeen antimicrobial resistant patterns were observed and 64 (91.4%) ST isolates were resistant to at least one antimicrobial agent and 49 (70%) ST isolates were resistant to two or more antimicrobials whereas 8.6% of isolates including a reference strain was shown susceptible to all tested antimicrobial agents. The most prevalent resistance pattern was a TE-S pattern (37.1%) in which 66.6% bovine, 40.8% swine and 21.1% human isolates were included. Three ST isolates from human (15.9%) showed resistance to 7 to 8 antimicrobials. PFGE types did not coincide with antimicrobial resistance patterns and therefore, the combination of antimicrobial susceptibility patterns and PFGE types allowed further differentiation for ST isolates tested. This data showed PFGE genotypes and antimicrobial resistance patterns of ST isolates from different origins in Korea.