Summary
The inhibitory activity of cefpirome (HR 810), a new cephalosporin derivative for parenteral use, was tested by agar dilution methods against Enterococcus faecatis (100 strains), Staphylococcus aureus (40 strains) and coagulase-negative staphylococcal species (60 strains) in comparison with other beta-lac ta m antibiotics.
For E. faecalls, the cefpirome minimum inhibitory concentration (MIC) range was 2-128 μg/ml, with an MIC,, of 8 μg/ml, and an MIC90, of 64 μg/ml. The optimal bactericidal activity against strains with MICs of ≤ 8 μg/ml occurred at 2-4 times the MIC, and the reduction in the initial inoculum was 99.9-99.7% after 24 h incubation at these concentrations.
Mec gene-negative staphylococci (both S. aureus and coagulase- negative species) had cefpirome MICs of 0.25-2 μg/ml (MIC50 0.5 μg/ml, MIC90 1 μg/ml). Mec gene-positive strains had MICs of 0.5-128 μg/ml (MIC50 2 μg/ml, MIC90 32 μg/ml). Strains with borderline resistance to oxacillin which did not harbor the mec gene and which were susceptible to cefpirome maintained their susceptibility even when high-density inocula were used and after several passages in media containing the antibiotic.
These studies present some potential advantages of cefpirome over other cephalosporins in the inhibitory activity against Gram-positive cocci.
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