PRESENCE OF A CAPSULE IN ERYSIPELOTHRIX-RHUSIOPATHIAE AND ITS RELATIONSHIP TO VIRULENCE FOR MICE

Three avirulent insertional mutants of Erysipelothrix rhusiopathiae we re obtained by the technique of transposon mutagenesis with the self-c onjugative transposon Tn916. The interactions between murine polymorph onuclear leukocytes and parent and mutant strains were studied in vitr o. In the presence of normal serum, the virulent parent strain was res istant to phagocytosis, whereas the avirulent mutant strains were effi ciently phagocytosed. In the presence of immune serum, the parent and the mutant strains were both efficiently phagocytosed. Electron micros copic examination of the parent strain demonstrated the presence of a structure resembling a capsule which was absent on the mutant strains, suggesting that a capsule may be involved in virulence. This was conf irmed in studies in which an avirulent mutant strain reverted to virul ence following acquisition of a capsule when the transposon was lost b y spontaneous excision. These results strongly suggest that virulence of E. rhusiopathiae is associated, at least in part, with resistance t o phagocytosis by polymorphonuclear leukocytes and that this antiphago cytic ability of the bacterium results from its possession of a capsul e.