Lactobacilli and human dental caries: more than mechanical retention.

Lactobacilli have been considered as major contributors to human dental caries for over a century. Recent in vitro model studies have shown that when compared to Streptococcus mutans, a keystone pathogen of human dental caries, the ability of lactobacilli to form biofilms is poor, although differences exist between the different major species. Further studies using molecular and bioinformatics approaches provide evidence that multiple mechanisms, including adhesin-receptor mediated physical contact with S. mutans, facilitate the adherence and establishment of lactobacilli on the tooth surface. There is also evidence that under conditions like continuous sugar consumption, weak acids and other antimicrobials such as bacteriocins from lactobacilli can become detrimental to the microbial community, especially those in the proximity. Details on the underlying mechanisms of how different Lactobacillus sp. establish and persist in the highly complex microbiota on the tooth surface await further investigation.

Nanoceria Aggregate Formulation Promotes Buffer Stability, Cell Clustering, and Reduction of Adherent Biofilm in Streptococcus mutans.

Streptococcus mutans is one of the key etiological factors in tooth-borne biofilm development that leads to dental caries in the presence of fermentable sugars. We previously reported on the ability of acid-stabilized nanoceria (CeO2-NP) produced by the hydrolysis of ceric salts to limit biofilm adherence of S. mutans via non-bactericidal mechanism(s). Herein, we report a chondroitin sulfate A (CSA) formulation (CeO2-NP-CSA) comprising nanoceria aggregates that promotes resistance to bulk precipitation under a range of conditions with retention of the biofilm-inhibiting activity, allowing for a more thorough mechanistic study of its bioactivity. The principal mechanism of reduced in vitro biofilm adherence of S. mutans by CeO2-NP-CSA is the production of nonadherent cell clusters. Additionally, dose-dependent in vitro human cell toxicity studies demonstrated no additional toxicity beyond that of equimolar doses of sodium fluoride, currently utilized in many oral health products. This study represents a unique approach and use of a nanoceria aggregate formulation with implications for promoting oral health and dental caries prevention as an adjunctive treatment.

Multiple factors are involved in regulation of extracellular membrane vesicle biogenesis in Streptococcus mutans.

Streptococcus mutans, a major etiological agent of human dental caries, produces membrane vesicles (MVs) that contain protein and extracellular DNA. In this study, functional genomics, along with in vitro biofilm models, was used to identify factors that regulate MV biogenesis. Our results showed that when added to growth medium, MVs significantly enhanced biofilm formation by S. mutans, especially during growth in sucrose. This effect occurred in the presence and absence of added human saliva. Functional genomics revealed several genes, including sfp, which have a major effect on S. mutans MVs. In Bacillus sp. sfp encodes a 4'-phosphopantetheinyl transferase that contributes to surfactin biosynthesis and impacts vesiculogenesis. In S. mutans, sfp resides within the TnSmu2 Genomic Island that supports pigment production associated with oxidative stress tolerance. Compared to the UA159 parent, the Δsfp mutant, TW406, demonstrated a 1.74-fold (p < .05) higher MV yield as measured by BCA protein assay. This mutant also displayed increased susceptibility to low pH and oxidative stressors, as demonstrated by acid killing and hydrogen peroxide challenge assays. Deficiency of bacA, a putative surfactin synthetase homolog within TnSmu2, and especially dac and pdeA that encode a di-adenylyl cyclase and a phosphodiesterase, respectively, also significantly increased MV yield (p < .05). However, elimination of bacA2, a bacitracin synthetase homolog, resulted in a >1.5-fold (p < .05) reduction of MV yield. These results demonstrate that S. mutans MV properties are regulated by genes within and outside of the TnSmu2 island, and that as a major particulate component of the biofilm matrix, MVs significantly influence biofilm formation.

Inhibitory effects of xylitol and sorbitol on Streptococcus mutans and Candida albicans biofilms are repressed by the presence of sucrose.

OBJECTIVE: Among the preventive and therapeutic options available for dental caries, sugar alcohols (xylitol and sorbitol) have been widely promoted as oral healthcare products due to its perceived anticariogenic effect. However, the therapeutic efficacy of these sugar alcohols against Streptococcus mutans and Candida albicans in a sucrose supplemented environment, as found in disease-prone conditions in the oral cavity, has not been adequately investigated. METHODS: Single and mixed-species biofilm formation was evaluated in medium with different concentrations of xylitol, sorbitol with or without sucrose supplementation. Biofilm quantification methods such as crystal violet assay, XTT assay, CFU counting complemented with confocal and electron microscopic techniques were used. RESULTS: Under sucrose-free conditions, xylitol and sorbitol demonstrated a significant dose-dependent inhibitory effect on S. mutans biofilms, whereas inhibitory effect on C. albicans biofilm was weak. The presence of 1 % sucrose in the environment diminished the inhibitory effect of both xylitol and sorbitol on S. mutans and C. albicans mono-species biofilms. Sucrose supplementation on pre-formed S. mutans biofilms also reduced the inhibitory effect of xylitol. Xylitol and sorbitol presence reduced mixed-species biofilm formation and altered the biofilm architecture and glucan production. However, sucrose supplementation reduced the inhibitory effect of sugar alcohols and enhanced the mixed-species biofilm formation. CONCLUSIONS: Xylitol and sorbitol exerts an inhibitory effect on S. mutans and C. albicans biofilm formation and this inhibitory effect is repressed by the presence of sucrose.

Lactobacillus Plantarum 108 Inhibits Streptococcus mutans and Candida albicans Mixed-Species Biofilm Formation.

Streptococcus mutans is the principal biofilm forming oral pathogen associated with dental caries. Studies have shown that Candida albicans, a commensal oral fungus is capable of forming pathogenic mixed-species biofilms with S. mutans. The treatment of bacterial and fungal infections using conventional antimicrobial agents has become challenging due to the antimicrobial resistance of the biofilm mode of growth. The present study aimed to evaluate the efficacy of secretory components of Lactobacillus plantarum 108, a potentially promising probiotic strain, against S. mutans and C. albicans single and mixed-species biofilms. L. plantarum 108 supernatant inhibited S. mutans and C. albicans single-species biofilms as shown by XTT reduction assay, crystal violet assay, and colony forming units counting. The probiotic supernatant significantly inhibited the S. mutans and C. albicans mixed-species biofilm formation. The pre-formed mixed-species biofilms were also successfully reduced. Confocal microscopy showed poorly developed biofilm architecture in the probiotic supernatant treated biofilms. Moreover, the expression of S. mutans genes associated with glucosyltransferase activity and C. albicans hyphal specific genes (HWP1, ALS1 and ALS3) were down-regulated in the presence of the probiotic supernatant. Altogether, the data demonstrated the capacity of L. plantarum 108 supernatant to inhibit the S. mutans and C. albicans mixed-species biofilms. Herein, we provide a new insight on the potential of probiotic-based strategies to prevent bacterial-fungal mixed-species biofilms associated with dental caries.

Graphene onto medical grade titanium: an atom-thick multimodal coating that promotes osteoblast maturation and inhibits biofilm formation from distinct species.

The time needed for the osseointegration of titanium implants is deemed too long. Moreover, the bacterial colonization of their surfaces is a major cause of failure. Graphene can overcome these issues but its wet transfer onto substrates employs hazardous chemicals limiting the clinical applications. Alternatively, dry transfer technique has been developed, but the biological properties of this technique remain unexplored. Here, a dry transfer technique based on a hot-pressing method allowed to coat titanium substrates with high-quality graphene and coverage area >90% with a single transfer. The graphene-coated titanium is cytocompatible, did not induce cell membrane damage, induced human osteoblast maturation (gene and protein level), and increased the deposition of mineralized matrix compared to titanium alone. Moreover, graphene decreased the formation of biofilms from Streptococcus mutans, Enterococcus faecalis and even from whole saliva on titanium without killing the bacteria. These findings confirm that coating of titanium with graphene via a dry transfer technique is a promising strategy to improve osseointegration and prevent biofilm formation on implants and devices.