An unexpected inhibitory effect of rapamycin against germination of spores of Bacillus brevis strain Nagano.

Rapamycin is used in medicine as an immunosuppressive agent (Sirolimus; Rapamune) although discovered as an antifungal agent. It is thought not to have antibacterial activity. Surprisingly, we found that rapamycin inhibits the germination of Bacillus brevis Nagano spores, but is inactive against Bacillus brevis Nagano vegetative cells. Surprisingly rapamycin did not show antimicrobial activity against other Bacillus strains, including other gramicidin S-producing Bacillus brevis strains such as ATCC 9999 and BI-7, whether tested as spores or vegetative cells.