Abstract

Purpose: Dental caries affects 2.5 Billion people worldwide from early childhood throughout life [1]. The disease state is associated with the formation of a multispecies, acidogenic biofilm that erodes dentin and tooth enamel over time. Treatment of biofilms is challenging due to host physiological barriers and biofilm structures, such as the extracellular polymeric substance that limit diffusion of chemotherapeutics to the pathogenic microorganisms within the biofilm, leading to increased antibiotic resistance. Our goal was to increase the efficacy of two orally relevant chemotherapeutics through the use of so-called inactive ingredients, or excipients, that we have previously shown to be effective at enhancing tobramycin efficacy in Pseudomonas aeruginosa biofilms. Methods: Multispecies biofilms, consisting of a 1:1:0.1 ratio of Streptococcus gordonii (DL1.1): Streptococcus mutans (UA159): Candida albicans (SC5314), were grown in 96 well microtiter plates for 24 h at 37 C and 5% CO prior to dosing. Biofilms were grown in 1:1 RPMI:Trypticase Soy Broth with 0.6% yeast extract microbiological media. Susceptibility testing of antimicrobial/excipient formulations was performed by adding premixed formulations of the proper dose to preformed biofilms and incubating for an additional 24 h at 37 C and 5% CO . Antimicrobials were tested at inhibitory and subinhibitory concentrations and excipients were tested at 5mM or 20mM concentrations. Cell viability was estimated with a PrestoBlue® viability assay and confirmed with subsequent microbial enumeration assays. Results: We tested 12 combinations of excipients during our preliminary screening. Our results indicate that ½ of the combinations of excipients with erythromycin, an antibacterial, enhances the efficacy of both inhibitory and sub-inhibitory doses of erythromycin. In comparison, only 1/3 of the excipient combinations tested with sub-inhibitory levels of chlorhexidine, an antiseptic, enhanced treatment efficacy. Of the screening studies performed, two excipients routinely enhanced the antimicrobial treatment efficacy. Conclusion: We have demonstrated that the addition of select excipients to antimicrobials can enhance the efficacy of the antimicrobial even at sub-inhibitory doses. This is important for combating the prevalence of antibiotic resistance found for microorganisms in the biofilm state.