[Antimicrobial activity of fosfomycin against beta-lactamase-producing methicillin-sensitive Staphylococcus aureus...

Antimicrobial activity of fosfomycin (FOM), cefazolin (CEZ), cefmetazole (CMZ), cefotiam (CTM) and piperacillin (PIPC) against clinical isolates of methicillin-sensitive Staphylococcus aureus (MSSA) (beta-lactamase-producing or non-producing) and methicillin-sensitive coagulase-negative Staphylococci (MSCNS) (beta-lactamase-producing or non-producing) were determined to make clear the differences in antimicrobial activity of FOM and beta-lactam antibiotics. The antimicrobial activity of PIPC against beta-lactamase-producing strains of MSSA was lower than that against non-producing ones, judging from the distribution patterns of susceptibility of the strains to PIPC. There were no differences in the antimicrobial activity of FOM, CEZ and CMZ for the producing and non-producing strains. The activity of FOM against MSCNS was comparable to that against MSSA, although those of CEZ, CMZ, CTM and PIPC were decreased. FOM, CEZ, CMZ and CTM showed bactericidal activity against TH4278 (MIC [microgram/ml]: FOM, 1; CEZ, 0.5; CMZ, 1; CTM, 0.5; PIPC, 1) of beta-lactamase-producing MSSA at 1 microgram/ml for 6 h, but PIPC did not at the same condition. FOM and CMZ at MIC suppressed regrowth of the strain, but CEZ, CTM and PIPC did not. In conclusion, FOM, which is not affected by beta-lactamase, demonstrated strong bactericidal activity at low concentration against the beta-lactam-resistant strains due to beta-lactamase production.