Exogenous CSP Induces S. Mutans Cell Death in Multispecies Biofilms

Objectives: Streptococcus mutans, which is the primary pathogen in dental caries, is one of the many microbial species found in dental biofilms. While biofilms can offer many advantages to its residents, different bacterial species can also produce a variety of antimicrobial compounds directed against other species through a cell-density dependent response known as quorum sensing. In many of the streptococci, including S. mutans, the QS signaling system depends on a competence-stimulating peptide, CSP, and a two-component signal transduction system. Recent studies have shown that the addition of exogenous CSP in higher than physiological concentrations results in competence-induced S. mutans cell death. The objectives of our study are to assess the efficacy of eCSP in inducing S. mutans cell death and to determine if prolonged applications of eCSP affect the population dynamics of S. mutans.
Methods: Sequentially formed multispecies biofilms were established by forming initial biofilms of Streptococcus gordonii, Actinomyces naeslundii, or a mixture of Streptococcus sanguinis, Streptococcus salivarius, S. gordonii and A. naeslundii on hydroxyapatite disks, following in 24h by inoculating S. mutans that containing a tetracycline-resistant plasmid. In another 24h, mixed biofilms were exposed to exogenous S. mutans CSP (eCSP) at concentrations of 0 and 100µM for 4 hours. Survival of S. mutans was assessed by counting colony forming units. The population dynamics of S. mutans in multispecies biofilms after long-term eCSP exposure (up to 72h) was also assessed by qPCR, using the primers of the rRNA genes corresponding to each species.
Results: eCSP induced significant S. mutans cell death in all of multispecies biofilms. The qPCR results showed that the population dynamics after long-term eCSP exposure incurred no significant shifts.
Conclusions: S. mutans eCSP exhibits high efficacy in inducing species-specific cell death in S. mutans, and may serve as a potential novel therapeutic strategy for dental caries reduction.