Closthioamide is isolated from the strictly anaerobic bacterium Clostridium cellulolyticum, and belongs to a new class of natural products [1]. Closthioamide is highly active against a pathogenic, methicillin-resistant Staphylococcus aureus (MRSA) strain with a minimum inhibitory concentration (MIC) of 0.4 μg/mL-1 (0.58 μM). Closthioamide is even active against vancomycin-resistant Enterococcus faecalis (VRE) with the same low MIC value and is thus significantly more potent against these bacteria than ciprofloxacin, the standard drug used against VRE, with remarkable strain selectivity. Closthioamide shows moderate antiproliferative and cytotoxic effects [2].