Tyzzer's infection: host specificity of Clostridium piliforme isolates.

Tyzzer's disease, a well-recognized syndrome in numerous laboratory animal species, is caused by the obligate intracellular bacterium, Clostridium piliforme. Distinct isolates of C. piliforme from various laboratory animal species have been identified based on protein and antigenic heterogeneity. The goal of this study was to examine the host specificity of three well-characterized isolates of C. piliforme. Groups of mice, rats, and hamsters were experimentally infected with isolates obtained from a naturally infected mouse (M1), a naturally infected rat (R1), and a naturally infected hamster (H2). To assess infection status, animals were monitored serologically for antibody to C. piliforme over a 12-week period. Evaluation of results indicated that the M1 isolate infected rats and mice but not hamsters, whereas the R1 and H2 isolates infected only the host species from which the isolates were originally obtained. These findings suggest that C. piliforme isolates can be categorized into two types: 1) cross-infective isolates, such as M1, which can infect more than one laboratory animal species, and 2) isolates, such as R1 and H2, which have a more limited host range within laboratory animal species. These results emphasize the need to consider the host specificity of C. piliforme isolates when investigating outbreaks of Tyzzer's disease.