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.