In vitro and in vivo activity of coumermycin and other antibacterial agents against methicillin-resistant strains of Staphylococcus aureus.

The in vitro activity of coumermycin, fusidic acid, cotrimoxazole, and vancomycin was determined by broth microdilution assay against 33 methicillin-resistant Staphylococcus aureus (MRSA) clinical isolates from the Detroit Receiving Hospital, Detroit, Mich. Coumermycin was the most active drug tested, while fusidic acid, vancomycin, and cotrimoxazole also had good activity. The four antimicrobials were tested in vivo against 7 strains of MRSA employing the mouse protection model. Again, coumermycin was the most active, followed by vancomycin, cotrimoxazole, and fusidic acid. Coumermycin was very active, while vancomycin and fusidic acid were inactive in neutropenic mice infected with an MRSA strain. Coumermycin retained activity when given 18 h before an MRSA infection, while vancomycin activity was lost. Coumermycin was active in a local thigh infection while vancomycin was inactive. The results indicate that coumermycin is potent against MRSA with activity equal or superior to comparable agents in various experimental mouse infections.