Selective recovery of oral Capnocytophaga spp. with sheep blood agar containing bacitracin and polymyxin B.

On the basis of in vitro susceptibility testing of antibiotics, dyes, and other antimicrobial agents, we developed and evaluated a medium, TBBP, for the selective isolation of oral Capnocytophaga spp. TBBP medium consists of 4% Trypticase soy agar (BBL Microbiology Systems, Cockeysville, Md.), 5% sheep blood, 0.1% yeast extract, 50 micrograms of bacitracin per ml, and 100 micrograms of polymyxin B per ml. A total of 34 Capnocytophaga stock cultures grew well on TBBP medium. Except for some streptococcal strains, TBBP medium inhibited growth of all test stock culture isolates of common oral gram-positive and gram-negative species. In a clinical study of 15 deep periodontal pockets, TBBP medium demonstrated Capnocytophaga recoverability that was similar to or higher than that shown by a nonselective blood agar medium. Typical Capnocytophaga colonial morphology enabled us to readily distinguish this organism from the few other bacteria which could grow on TBBP medium.