Serotyping and pathogenicity of Erysipelothrix strains isolated from tonsils of slaughter pigs in Thailand

Erysipelothrix strains were isolated from the tonsils of 46 (15.0%) of 307 apparently healthy slaughter pigs in Thailand during the period of August to September, 1997. A total of 27 of the 46 Erysipelothrix isolates could be classified into 5 serovars but the remaining 19 were untypable in this study. Of the 25 isolates serologically identified as Erysipelothrix rhusiopathiae, 20, 4, and 1 isolates belonged to serovars 2, 12, and 17, respectively. Only 2 isolates from the tonsils belonged to Erysipelothrix tonsillarum and represented either serovar 7 or 10. Although the periods and the districts of the survey were limited, the information obtained in the present investigation demonstrates the presence of a variety of serovars in pigs in Thailand. Of 29 selected isolates belonging to serovars 2, 7, 10, 12, 17, and untypable, only 5 (17.2%) were virulent for both mice and pigs. Five of these virulent isolates belonging to serovars 2 and 12 killed less than 30% of mice immunized with a swine erysipelas bacterin commercially available in Thailand, suggesting that the vaccine elicited a sufficient immunity to these field isolates.