Comparative antimicrobial activities of antiseptic mouthrinses against isogenic planktonic and biofilm forms of Actinobacillus actinomycetemcomitans

Background: Bacteria contained in biofilms have been shown to have a decrea sed susceptibility to antimicrobial agents compared to those in planktonic form. Thus, in vitro biofilm models have been developed for screening oral antimicrobial formulations in an effort to produce findings more predictive of clinical activity. This study compared the antimicrobial activity of th ree mouthrinse formulations when tested against isogenic strains of Actinob acillus actinomycetemcomitans (Aa), one of which was a clinical isolate whi ch forms tenacious biofilms in vitro and the other of which was a spontaneo us variant which always grows planktonically. Method: Biofilm-forming Aa strains CU1000 and NJ4300, obtained as clinical isolates, and their respective spontaneous planktonic variants, CU1060 and NJ4350, were grown under standard laboratory conditions and exposed for 15 s to either a negative control (phosphate buffered saline [PBS]), an essent ial-oil containing mouthrinse (Listerine((R)) Antiseptic [LA]), an amine fl uoride/stannous fluoride-containing mouthrinse (Meridol((R)) [M]), or a tri closan and PVM/MA copolymer-containing mouthrinse (Plax((R)) [P]). The cell s were then washed, serially diluted, plated, and incubated for enumeration of viable bacteria. Colony-forming units (CFU)/ml were log(10) transformed and the mouthrinse groups were compared to the PBS group using analysis of variance. Results: All 3 mouthrinses produced statisically significant 99.99% reducti ons (p less than or equal to0.0001) in both planktonic strains compared to the PBS control. Effects on the biofilm forms of the organisms were more va riable, Exposure to LA produced statistically significant (p less than or e qual to0.0001) reductions in strains CU1000 and NJ4300 of 98.20% and 96.47% , respectively, compared to PBS. M and P produced much smaller reductions w hich were not statistically significant. Conclusions: The results of this study, in which antimicrobial mouthrinses were tested against biofilm-forming and planktonic strains of the same orga nism, provide a clear demonstration of the resistance to antimicrobial agen ts conferred by biofilm formation and provide additional support for employ ing tests using biofilms to more accurately assess the relative activities of antiplaque agents in vitro.