Experimental investigations into the pathogenicity of the L-phase variant of Streptobacillus moniliformis.

SUMMARY The experimental evidence presented in the present work shows that the L-phase variant of Streptobacillus moniliformis is in itself only slightly virulent to mice, if it is so at all. On intraperitoneal inoculation the infection remained latent until reversion to the bacillary form had occurred; it did not manifest itself if the reversion was more or less inhibited by an appropriate administration of penicillin. In contrast to the results obtained in previous experiments with the bacillary phase of S. moniliformis, it proved extremely difficult to infect mice intranasally with L1 cultures, and attempts to establish an infection by feeding completely failed. In addition, it is shown by immunization experiments that the bacillary phase of S. moniliformis is a better immunizing antigen than the L-phase variant is, as a vaccine prepared from the latter, though effective against infection with the homologous phase, was unable to prevent infection with streptobacillus cultures. Vaccination with a bacillary vaccine, on the other hand, conferred immunity against infection with both the homologous phase and the heterologous phase. The L-phase of S. moniliformis may therefore be regarded as a degraded variant: compared with the bacillary form, it is characterized by a deficiency of important biological properties.