L-Arginine, a ubiquitous amino acid in human saliva, serves as a substrate for alkali production by arginolytic bacteria. Recently, exogenous L-arginine has been shown to enhance the alkalinogenic potential of oral biofilm and destabilize its microbial community, which might help control dental caries. However, L-arginine exposure may inflict additional changes in the biofilm milieu when bacteria are growing under cariogenic conditions. Here, we investigated how exogenous L-arginine modulates biofilm development using a mixed-species model containing both cariogenic (Streptococcus mutans) and arginolytic (Streptococcus gordonii) bacteria in the presence of sucrose. We observed that 1.5% (wt/vol) L-arginine (also a clinically effective concentration) exposure suppressed the outgrowth of S. mutans, favored S. gordonii dominance, and maintained Actinomyces naeslundii growth within biofilms (versus vehicle control). In parallel, topical L-arginine treatments substantially reduced the amounts of insoluble exopolysaccharides (EPS) by >3-fold, which significantly altered the three-dimensional (3D) architecture of the biofilm. Intriguingly, L-arginine repressed S. mutans genes associated with insoluble EPS (gtfB) and bacteriocin (SMU.150) production, while spxB expression (H 2 O 2 production) by S. gordonii increased sharply during biofilm development, which resulted in higher H 2 O 2 levels in arginine-treated biofilms. These modifications resulted in a markedly defective EPS matrix and areas devoid of any bacterial clusters (microcolonies) on the apatitic surface, while the in situ pH values at the biofilm-apatite interface were nearly one unit higher in arginine-treated biofilms (versus the vehicle control). Our data reveal new biological properties of L-arginine that impact biofilm matrix assembly and the dynamic microbial interactions associated with pathogenic biofilm development, indicating the multiaction potency of this promising biofilm disruptor. IMPORTANCEDental caries is one of the most prevalent and costly infectious diseases worldwide, caused by a biofilm formed on tooth surfaces. Novel strategies that compromise the ability of virulent species to assemble and maintain pathogenic biofilms could be an effective alternative to conventional antimicrobials that indiscriminately kill other oral species, including commensal bacteria. L-Arginine at 1.5% has been shown to be clinically effective in modulating cariogenic biofilms via alkali production by arginolytic bacteria. Using a mixed-species ecological model, we show new mechanisms by which L-arginine disrupts the process of biofilm matrix assembly and the dynamic microbial interactions that are associated with cariogenic biofilm development, without impacting the bacterial viability. These results may aid in the development of enhanced methods to control biofilms using L-arginine. Biofilms formed on surfaces are highly organized and structured microbial communities enmeshed in an extracellular matrix composed of polymeric substances, such as exopoly...

selectivity for S. mutans , and not other oral bacteria, and affects targeted bacteria within seconds of contact. Methods: In the present study, we evaluated C16G2 for clinical utility in vitro, followed by a pilot efficacy study to examine the impact of a 0.04% (w/v) C16G2 rinse in an intra-oral remineralization/demineralization model. Results and Conclusions: C16G2 rinse usage was associated with reductions in plaque and salivary S. mutans , lactic acid production, and enamel demineralization. The impact on total plaque bacteria was minimal. These results suggest that C16G2 is effective against S. mutans in vivo and should be evaluated further in the clinic. Copyright © 2011 S. Karger AG, Basel Dental caries is a chronic infection that affects populations worldwide. In the United States alone, health care costs associated with treating dental caries have topped 64 billion USD annually [Evans and Kleinman, 2000; Anonymous, 2008]. In the developing world, dental caries is more prevalent, especially among pediatric patients, Key WordsAntimicrobial ؒ Antimicrobial peptide ؒ Caries ؒ Demineralization ؒ Dental plaque ؒ Lactic acid ؒ Mouth rinse ؒ Oral therapeutic ؒ Selective antibiotic ؒ Selective therapeutic ؒ Specifically targeted antimicrobial peptide ؒ Streptococcus mutans ؒ Targeted antimicrobial Abstract Background/Aims: Streptococcus mutans , the major etiological agent of dental caries, has a measurable impact on domestic and global health care costs. Though persistent in the oral cavity despite conventional oral hygiene, S. mutans can be excluded from intact oral biofilms through competitive exclusion by other microorganisms. This suggests that therapies capable of selectively eliminating S. mutans while limiting the damage to the normal oral flora might be effective long-term interventions to fight cariogenesis. To meet this challenge, we designed C16G2, a novel synthetic specifically targeted antimicrobial peptide with specificity for S. mutans . C16G2 consists of a S. mutans -selective 'targeting region' comprised of a fragment from S. mutans competence stimulation peptide (CSP) conjoined to a 'killing region' consisting of a broad-spectrum antimicrobial peptide (G2). In vitro studies have indicated that C16G2 has robust efficacy and