Disc susceptibility testing for thermomphilic campylobacters.

The minimum inhibitory concentrations (MICs) and zone diameters around NCCLS strength discs of 100 clinical isolates of thermophilic Campylobacter species, including 79 strains of Campylobacter jejuni subsp. jejuni, 19 of C. coli and two of C. lari, plus three type strains of these species, were determined for erythromycin, clindamycin, nalidixic acid, norfloxacin, ciprofloxacin, ampicillin, piperacillin, cephalothin, ceftriaxone, chloramphenicol, gentamicin and tetracycline. Using error-rate bounded analysis and adjustment of MIC breakpoints to fit natural populations, tentative interpretive zone diameter criteria were set for each of the antimicrobials. Application of these criteria showed that resistance to quinolones was not detected in species other than C. lari. Two strains of C. jejuni subsp. jejuni were susceptible to cephalothin. The type strain of C. lari was susceptible to erythromycin and resistant to clindamycin. Full resistance to erythromycin, chloramphenicol or gentamicin was not found in any strain, while nine strains were resistant to tetracycline. This disc method should provide a simple approach to resistance detection for surveillance or routine testing of invasive isolates.