Cefmetazole: a broad spectrum cephem antibiotic effective on methicillin- and cephem-resistant Staphylococcus aureus

Antibacterial activity of cefmetazole (CMZ) was investigated by the plate dilution method. Since CMZ is stable to any type of bacterial beta-lactamases, it inhibited growth of Escherichia coli carrying R plasmids, Klebsiella spp., Proteus vulgaris, and Bacteroides fragilis at the concentration of less than 0.78 to 25.0 micrograms/ml. The distinct characteristic of CMZ is its anti-MRSA (methicillin- and cephem-resistant Staphylococcus aureus) activity. Exclusively in MRSA, a new fraction of penicillin binding proteins (PBP) with a relative molecular mass of 78 kd apears, and the 78 kd/PBP possesses low binding affinity to beta-lactam antibiotics. By the competitive binding experiment of beta-lactam drugs to the PBPs of MRSA, it was revealed that CMZ and cephaloridine retain binding affinities to the new 78kd/PBP fraction of MRSA.