In vitro antimicrobial activity of the new antibiotic vermisporin

The antimicrobial activity of vermisporin, a new antibiotic produced by fermentation of the fungus Ophiobolus vermisporis, was tested in vitro. Vermisporin inhibited 90% of Bacteroides fragilis and other Bacteroides spp. at 1 microgram/ml (range 0.25-1 micrograms/ml). Clostridium perfringens were inhibited by 1 microgram/ml (range 0.25-2 micrograms/ml). Vermisporin inhibited 90% of Staphylococcus aureus, including methicillin-resistant Staphylococcus aureus, at 0.5 micrograms/ml (range 0.12-0.5 micrograms/ml). Vermisporin MICs for group A, B, C, F and G streptococci were < 1 microgram/ml when tested in Haemophilus Test Medium but > or = 8 micrograms/ml in the presence of blood. Vermisporin MICs for Enterobacteriaceae, Pseudomonas aeruginosa and Haemophilus influenzae exceeded 64 micrograms/ml. Inhibited organisms had MBCs 16- to 32-fold above the MICs.