Cefpirome (HR810) disk diffusion susceptibility tests: confirmation of interpretive criteria using cefotaxime and cefoperazone-resistant strains and effects of blood supplemented media

Abstract

Cefpirome (formerly HR810) is a wide-spectrum, beta-lactamase-stable cephalosporin with antimicrobial activity against Pseudomonas species, Enterobacteriaceae, and gram-positive species. Reevaluation of the 30-microgram disk diffusion tests with commercially prepared disks using strains resistant to "third generation," cephalosporins confirms the proposed susceptibility breakpoint zone of greater than or equal to 18 mm (minimal inhibitory concentration correlate, less than or equal to 8.0 micrograms/ml) and the resistance breakpoint zone of less than or equal to 14 mm (minimal inhibitory concentration correlate, greater than or equal to 32 micrograms/ml). Major and minor interpretive errors were only 3.8%, and these errors could be further reduced (2.3%) by not testing methicillin-resistant Staphylococcus species. The addition of 5% sheep blood or chocolated blood to Mueller-Hinton agar slightly increased the cefpirome zone diameters (17.7-22.2 mm) for nearly 60% of Streptococcus faecalis strains tested.