In vitro susceptibility of Capnocytophaga species to 29 antimicrobial agents.

A hemoglobin-supplemented medium composed of Columbia agar base supplemented with 1% hemoglobin and 1% Polyvitex was used to investigate the in vitro activity of 29 antimicrobial agents against Capnocytophaga species. Clindamycin was the most active agent, with all strains being inhibited by 0.06 microgram/ml or less. Amoxicillin-clavulanic acid and imipenem were the most active among the beta-lactam antibiotics (MIC for 90% of strains tested [MIC90], 0.50 microgram/ml); other very active drugs were BMY 28142, cefpirome, cefotaxime, ceftazidime, and ceftriaxone (MIC90, 0.06 to 0.50 micrograms/ml), although at least one strain showed resistance to each of these antibiotics (MIC, greater than or equal to 16 micrograms/ml). Ciprofloxacin was the most active among the quinolones, with all strains being inhibited by 0.50 microgram/ml. The MICs of the other four drugs ranged from 0.12 to 4 micrograms/ml. Ampicillin, penicillin G, ticarcillin, aztreonam, and temocillin were moderately active (MIC90, 1 to 8 micrograms/ml; MIC range, less than or equal to 0.03 to greater than 128 micrograms/ml). All strains were uniformly resistant to the aminoglycosides, polymyxin B, vancomycin, trimethoprim, and amphotericin B. Three strains produced beta-lactamase. No significant difference was found between the susceptibility of strains isolated from various sources or patients.