A Pyrroloquinazoline Analogue Regulated Streptococcus mutans and Streptococcus sanguinis Dual-Species Biofilms

Objective: Selective inhibition of cariogenic bacteria is regarded as a potential strategy against caries. To assess the potential of SCH-79797, one novel promising antibiotic, in microbial equilibrium using a dual-species biofilms model of Streptococcus mutans (S. mutans) and Streptococcus sanguinis (S. sanguinis).

Methods: Biofilm biomass and metabolic activity were disclosed using the MTT and crystal violet staining methods. Besides, bacteria/exopolysaccharide staining and anthrone method were applied to measure extracellular polysaccharides (EPS) synthesis, while lactic acid measurement was used to assess acid production. Then, quantitative real-time PCR (qRT-PCR) was employed to investigate gene variation related to polysaccharide production and interspecies competition within dual-species biofilm. The dual-species biofilm configuration was mirrored by fluorescence in situ hybridization (FISH). Growth of the planktonic bacteria was reflected by growth curve. Lastly, bacterial cell membranes were visualized by transmission electron microscope (TEM).

Results: Within dual-species biofilm, SCH-79797 not only abated biomass, metabolic activity, EPS as well as acid generation but also decreased the proportion of opportunistic cariogenic S. mutans. Besides, polysaccharides production and competition-related genes (gtfP, spxB) in S. sanguinis were up-regulated, whereas these associated genes (gtfB, gtfC, gtfD, and nlmD) in S. mutans were down-regulated inside dual-species biofilm which displayed decreased S. mutans ratio. Additionally, SCH-79797 had a selective inhibitory effect on S. mutans rather than S. sanguinis, including biofilm's biomass, metabolic activity, acid and polysaccharides generation, bacterial growth, and cell membrane integrity.

Conclusions: SCH-79797 showed regulatory effects on controlling dual-species biofilm ecologically, indicating its potential to be a latent anticaries agent.