Media- and method-dependent variations in minimal inhibitory concentrations of antiplaque agents on oral bacteria

Aims: To determine minimal inhibitory concentrations (MICs) and the percentage of nonsusceptible bacteria - those still cultivable above a threshold concentration - in human supragingival dental plaque and saliva for antiplaque/antimicrobial agents including triclosan (TCS) and trichlorocarbanilide (TCC), and a new potential antimicrobial, 2-t-butyl-5-(4-t-butylphenyl)-phenol (DTBBP). Methods and Results: Broth and agar dilution-based MIC tests were performed using 28 oral and nonoral bacterial strains representing 17 species. MICs for TCS were lowest and more than 100-fold lower than DTBBP (P < 0.0005) by both methods. MICs for TCS were lower in broth-based tests compared with TCC. The additions of defibrinated blood to agar and horse serum to broth increased MICs - in the case of TCS, 10- to 15-fold. Significantly higher proportions of nonsusceptible plaque and salivary bacteria were recovered from agar media containing DTBBP or TCC compared with TCS (P < 0.05). Conclusions: TCS is a more effective antimicrobial agent than either TCC or DTBBP as determined by in vitro testing. Significance and Impact of the Study: The utility of in vitro testing for antiplaque agents as a predictor of in vivo efficacy is affected by the methods used.