Haemophilus test medium interpretive criteria for disk diffusion susceptibility tests with cefdinir, cefetamet,...

The disk diffusion zones and the MICs of six newer antimicrobials with significant activity against Haemophilus influenzae were compared using the Haemophilus test medium (HTM) and National Committee for Clinical Laboratory Standards methods. The rank order of potency was cefpodoxime (MIC50, < or = 0.03 micrograms/ml) > cefetamet > cefdinir > cefdaloxime = trospectomycin > cefmetazole (MIC50, 2 micrograms/ml). Susceptible breakpoint interpretive criteria for HTM tests were established that conformed to prior recommendations for each drug when tested against other species. Absolute agreement between methods ranged from 89% to 100% with < or = 1% false-susceptible interpretive errors. The recommended, tentative disk diffusion susceptible interpretive criteria were for 5-micrograms cefdinir disks > or = 20 mm (MIC correlate, < or = 1 micrograms/ml); for 10-micrograms cefetamet disks > or = 18 mm (MIC correlate, < or = 4 micrograms/ml); for 30-micrograms cefetamet disks > or = 21 mm (MIC correlate, < or = 4 micrograms/ml); for 30-micrograms cefmetazole disks > or = 16 mm (MIC correlate, < or = 16 micrograms/ml); for 10-micrograms cefpodoxime disks > or = 21 mm (MIC correlate, < or = 2 micrograms/ml); for 30-micrograms cefdaloxime disks > or = 23 mm (MIC correlate, < or = 2 micrograms/ml) and for 30-micrograms trospectomycin disks > or = 17 mm (MIC correlate, < or = 16 micrograms/ml). beta-Lactamase-negative, ampicillin-resistant (BLNAR) H. influenzae isolates consistently had the highest MICs for each cephalosporin tested.(ABSTRACT TRUNCATED AT 250 WORDS)