Regulatory Effect of Irresistin-16 on Competitive Dual-Species Biofilms Composed of Streptococcus mutans and Streptococcus sanguinis

Based on the ecological plaque hypothesis, suppressing opportunistic pathogens within biofilms, rather than killing microbes indiscriminately, could be a biofilm control strategy for managing dental caries. The present study aimed to evaluate the effects of irresistin-16 (IRS-16) on competitive dual-species biofilms, which consisted of the conditional cariogenic agent Streptococcus mutans (S. mutans) and oral commensal bacteria Streptococcus sanguinis (S. sanguinis). Bacterial growth and biofilm formation were monitored using growth curve and crystal violet staining, respectively. The microbial proportion was determined using fluorescence in situ hybridization. A 2, 5-diphenyltetrazolium bromide assay was used to measure the metabolic activity of biofilms. Bacterial/extracellular polysaccharide (EPS) dyeing, together with water-insoluble EPS measurements, were used to estimate EPS synthesis. A lactic acid assay was performed to detect lactic acid generation in biofilms. The cytotoxicity of IRS-16 was evaluated in mouse fibroblast L929 cells using a live/dead cell viability assay and cell counting kit-8 assay. Our results showed that IRS-16 exhibited selective anti-biofilm activity, leading to a remarkable survival disadvantage of S. mutans within competitive dual-species biofilms. In addition, the metabolic activity, EPS synthesis, and acid generation of dual-species biofilms were significantly reduced by IRS-16. Moreover, IRS-16 showed minimal cytotoxicity against mouse fibroblast L929 cells. In conclusion, IRS-16 exhibited remarkable regulatory effects on dual-species biofilms composed of S. mutans and S. sanguinis with low cytotoxicity, suggesting that it may have potential for use in caries management through ecological biofilm control.

Understanding the Complex Phage-Host Interactions in Biofilm Communities

Bacteriophages and bacterial biofilms are widely present in natural environments, a fact that has accelerated the evolution of phages and their bacterial hosts in these particular niches. Phage-host interactions in biofilm communities are rather complex, where phages are not always merely predators but also can establish symbiotic relationships that induce and strengthen biofilms. In this review we provide an overview of the main features affecting phage-biofilm interactions as well as the currently available methods of studying these interactions. In addition, we address the applications of phages for biofilm control in different contexts. Expected final online publication date for the Annual Review of Virology, Volume 8 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Single DNase or Proteinase Treatment Induces Change in Composition and Structural Integrity of Multispecies Oral Biofilms

Biofilm virulence is mainly based on its bacterial cell surrounding biofilm matrix, which contains a scaffold of exopolysaccharides, carbohydrates, proteins, lipids, and nucleic acids. Targeting these nucleid acids or proteins could enable an efficient biofilm control. Therefore, the study aimed to test the effect of deoxyribonuclease I (DNase I) and proteinase K on oral biofilms. Six-species biofilms (Streptococcus mutans, Streptococcus oralis, Actinomyces oris, Fusobacterium nucleatum, Veillonella dispar, and Candida albicans) were exposed to DNase I (0.001 mg/mL, 0.002 mg/mL) or proteinase K (0.05 mg/mL, 0.1 mg/mL) for 1 h during biofilm formation. After 64 h, biofilms were harvested, quantified by culture analysis and visualized by image analysis using CLSM (confocal laser scanning microscopy). Statistical analysis was performed by ANOVA, followed by the Tukey test at a 5% significance level. The biofilm treatment with proteinase K induced a significant increase of Logs10 counts in S. mutans and a decrease in C. albicans, while biofilm thickness was reduced from 28.5 μm (control) to 9.07 μm (0.05 mg/mL) and 7.4 μm (0.1 mg/mL). Treatment with DNase I had no effect on the total bacterial growth within the biofilm. Targeting proteins of biofilms by proteinase K are promising adjunctive tool for biofilm control.