MULTICENTER VALIDATION OF PROPOSED DISK DIFFUSION SUSCEPTIBILITY TESTING INTERPRETIVE CRITERIA FOR LOMEFLOXACIN USING MORE THAN 1,500 CLINICAL ISOLATES

The accuracy of disk diffusion susceptibility testing of lomefloxacin was evaluated using 1,555 recent clinical isolates from ten medical ce nters. The isolates were rapidly growing nonfastidious aerobic species (1,501 isolates) and Haemophilus species (54 isolates), each found as an indicated species in the product package insert. Applying the rece ntly proposed modification of disk diffusion interpretive criteria (su sceptible at greater than or equal to 20 mm and resistant at less than or equal to 16 mm), absolute categorical agreement for nonfastidious aerobes (1,501 strains) was 95.5% with 0.5% very major and 0.1% major errors (error rates calculated using all tested strains as the denomin ator). The intermethod discord (MIG vs disk diffusion) was 0.5%. This contrasts to the current NCCLS recommended criteria (susceptible at gr eater than or equal to 22 mm and resistant at less than or equal to 18 mm) where the absolute categorical agreement was significantly less ( 89.6%) with 0.2% very major, and 0.3% major errors, and the intermetho d discord plas 7.1%. For Haemophilus species (54 strains), intermethod agreement was complete using either the current NCCLS interpretive cr iteria or the modified criteria. These multicenter (ten laboratories) data support the acceptance of the proposed modification of disk diffu sion interpretive criteria for 10-mu g lomefloxacin disks.