– (-)-Viriditoxin is a mycotoxin originally isolated from A. viridinutans that has antibacterial and antiproliferative activity. It is active against methicillin-sensitive and -resistant S. aureus (MSSA and MRSA, respectively), tetracycline-sensitive and -resistant Staphylococcus, vancomycin-sensitive and -resistant Enterococcus, and penicillin-sensitive and -resistant S. pneumoniae (MICs = 2-32 μg/ml). (-)-Viriditoxin is also active against fish pathogens, including S. iniae and S. parauberis (MICs = 0.16-0.21 μg/ml). It inhibits polymerization and the GTPase activity of E. coli FtsZ, a tubulin-like GTPase involved in bacterial cell division (IC50s = 8.2 and 7 μg/ml, respectively). (-)-Viriditoxin inhibits proliferation of human DU145, LNCaP, and PC3 prostate cancer cells (IC50s = 5.36, 0.63, and 7.6 μM, respectively). It is also toxic to mice (LD50 = 2.8 mg/kg, i.p.).