Prevalence and Genotype of Salmonella Choleraesuis in Gunma Prefecture, Japan

We studied the prevalence of swine salmonellosis and PFGE genotype of isolates in Gunma Prefecture, Japan. Between 2005 and 2008, swine salmonellosis was confirmed in 430 of 2,707,402 (0.02%) swine at slaughterhouses. All isolates were identified as deriving from Salmonella Choleraesuis, biotype Choleraesuis (negative for H2S production). We used 30 bacterial strains from 15 farms that had experienced outbreaks in 2006 and 2007. All strains were susceptible to various antibiotics such as cephems (cefotaxime), fluoroquinolones (norfloxacin and ciprofloxacin), and fosfomycin. On the other hand, all strains were resistant to tetracycline (TC), and 29 of 30 (97%) strains were resistant to streptomycin (SM). The most predominant profiles were those of SM-TC (26 strains). During Bin 1 digestion, 30 strains showed 6 profiles on PFGE as G1 to 06, and each profile was assigned into 1 of 4 clusters (I to IV). The most prevalent profile was Cl (22 strains), followed by G3 (3 strains), and G2 (2 strains). Strains showing the same antimicrobial resistance profiles (SM-TC) and the same PFGE profiles (Cl) were isolated from 5 of 15 farms (A to E) during the 2006 and 2007 outbreaks. In conclusion, the prevalence of swine salmonellosis caused by SM-TC resistant-S. Choleraesuis biotype Choleraesuis is around 0.02%, as determined by infection rate at pig farms between 2005 and 2008 in Gunma prefecture. S. Choleraesuis usually causes systemic infections in swine and humans and antimicrobial treatment is necessary. The antimicrobial susceptibility of Salmonella in swine should be surveyed further.