A total of 75 isolates of Erysipelothrix rhusiopathiae, which had been cultured from 48 slaughter pigs with arthritis and lymphadenitis in Nagasaki Prefecture of Japan between 1985 and 1986, were examined for serotype, pathogenicity and antimicrobial susceptibility.
Of these isolates, 50 (66.7%) were serotype la, 13 (17.3%) were serotype 2, 8 (10.7%) were serotype 6, and 1 (1.3%) each was serotype 1b, 10, 11 or 21.
A pathogenicity test for mice showed that 42 isolates (56.0%) were clinically avirulent, 20 (26.7%) were highly virulent, and 13 (17.3%) were of low virulence. Most isolates of serotype 2 and all isolates of serotypes 6 and 21 were highly virulent whereas most isolates of serotype la were avirulent. Erysipelothrix rhusiopathiae was recovered from the left knee joint of mice inoculated with 33 of 42 (78.6%) avirulent isolates. Mice immunised with live erysipelas vaccine did not die after they were challenged with the highly virulent strains.
All of the 60 isolates tested were highly susceptible to penicillin, ampicillin, erythromycin and tylosin, but exhibited low susceptibility to oxytetracycline (MIC: 12.5-100μg/ml).