Pathogenicity of Beauveria bassiana in mice.

The potential pathogenicity of Beauveria bassiana was examined by intramuscular injection of high (2 x 10(8)) or low (2 x 10(5)) concentrations of conidia spores, into the left or right quadriceps muscles of CD-1 mice, respectively. The injection sites were monitored over a period of 28 days by both microbiological and histopathological methods. Focal muscle necrosis, edema and inflammation occurred rapidly (within 12 hours) at the high dose application (2 x 10(8)) site, but such lesions were far less severe with the low dose spore application (2 x 10(5)). Fungal spores in the high dose site persisted in normal shape for 2 weeks, after which time they began to degenerate. Almost all spores were cleared from the injection site within the 28-day observation period. Spread to other organs of the body was not observed, except by macrophage transport to regional lymph nodes. At the low dose rate, most spores were cleared within 12 h to 2 d, leaving only mild focal edema and inflammation. Viable fungal colonies could be recovered up to 3 d after injection from the high dose site, but only up to 12 h from the low dose site. It was concluded that B. bassiana does not cause infection, nor multiply, nor survive for more than 3 days when injected intramuscularly into healthy mice.