Biochemical, pathogenicity and toxicity studies of type III strains of Yersinia pseudotuberculosis isolated from the cecal contents of pigs.

Recent investigations have shown that the pig is a symptomless intestinal carrier of Y. pseudotuberculosis, the great majority of the strains isolated belonging to type III. Although these type III strains have a world-wide distribution there is little evidence to suggest that they are transferred readily to other animals and man. For that reason we examined the biochemical, pathogenic, immunogenic and exotoxin-producing properties of 24 type III strains isolated from the cecal contents of apparently healthy pigs. For comparison, we also examined type III strains from other sources, type I strains from normal pigs and isolates belonging to the other serotypes of Y. pseudotuberculosis. Biochemical reactions of type III strains were in accordance with data in the literature except for maltose and melibiose. Type III porcine strains were uniformly avirulent and atoxic but possessed a considerable degree of immunogenicity. On the other hand, type III strains isolated from aborted lambs and calves, although atoxic, were virulent for the guinea pig, as were also type I strains from healthy pigs. The pathogenic mechanism of Y.pseudotuberculosis, which is not unlike that found in E. coli, is discussed.