In vitro activity of fosfomycin against 'problem' gram-positive cocci.

Fosfomycin was active in vitro against 54 of 60 'problem' Gram-positive cocci (20 methicillin-resistant Staphylococcus aureus, 20 coagulase-negative staphylococci and 20 enterococci). Its activity was significantly greater under anaerobic conditions, especially against coagulase-negative staphylococci. Mutants resistant to fosfomycin were readily demonstrated, but their growth was prevented by rifampicin or ciprofloxacin. The combinations rifampicin+fosfomycin and ciprofloxacin+fosfomycin showed MIC synergy. It is concluded that fosfomycin in an appropriate combination would be a valuable addition to the small and dwindling range of antibiotics active against problem Gram-positive cocci.