Effect of the Probiotic <b><i>Lactobacillus rhamnosus</i></b> LB21<b> </b>on the Cariogenicity of <b><i>Streptococcus mutans</i></b> UA159 in a Dual-Species Biofilm Model

Abstract

Despite promising results using probiotics, evidence of the preventive effect on enamel demineralization is insufficient and the cariogenic potential of probiotics is still controversial. Probiotics could affect biofilm formation and interfere with adherence, growth or coaggregation with Streptococcus mutans in biofilms. However, most of the studies have been conducted using planktonic bacteria. Hence, the aim of the study was to assess the effect of probiotic bacteria on the cariogenicity of S. mutans using an in vitro biofilm caries model on enamel. Single-species biofilms (S. mutans UA159, SM or Lactobacillus rhamnosus LB21, LB) or dual-species biofilms simultaneously inoculated (SM + LB) or LB inoculated 8 h after SM (SM → LB) were grown for 96 h. Biofilms were formed on bovine enamel saliva-coated slabs of known surface hardness (SH) and immersed in culture media. Biofilms were exposed 8 times per day to 10% sucrose. Medium pH was monitored twice daily as a biofilm acidogenicity indicator. After 96 h, biofilms were collected to determine biomass and bacteria viability. Slab demineralization was calculated as percentage of SH loss (%SHL). Additionally, the model was tested with different concentrations of the initial inoculum (10³, 10⁶, 10⁸ cells/ml) and different adhesion times (2 or 8 h). The dual-species biofilm revealed no LB effects on SM cariogenicity, without changes in acidogenicity or %SHL among groups (p > 0.05, n = 12). Lack of activity of LB on SM cariogenicity persisted even when 10⁵ times higher concentration of the probiotic was tested. Coaggregation was not observed. In conclusion, findings suggest that LB does not reduce cariogenicity of SM in a validated experimental caries model.

Biofilm extracellular polysaccharides degradation during starvation and enamel demineralization

“…An in vitro , randomized and blinded factorial (2x2) study was conducted using a validated cariogenic biofilm model [5, 25, 26]. The study was approved by the Research and Ethics Committee of the Piracicaba Dental School, University of Campinas (142/2014).…”

“…Only in the adhesion phase, the UTYEB pH 7.0 was strongly buffered (10x higher than the usual phosphate concentration) to avoid pH drop and enamel demineralization during this phase. After adhesion, the slabs were transferred to fresh UTYEB pH 7.0 with 0.1 mM glucose (salivary basal concentration) and incubated overnight at 37°C, 10% CO 2 for 16 h. At the beginning of 2 nd day, the biofilms were exposed to episodes of “feast” and “famine” comprised of 8 daily exposures to carbohydrate solutions: 10% sucrose or a combination of 5.25% glucose and 5.25% fructose at predetermined times (08:00, 09:30, 11:00, 12:00, 13:30, 15:00, 16:00 and 17:30 h) for 3 min [25, 26]. After the cariogenic challenge, enamel slabs were rinsed 3 times in 0.9% NaCl solution, and placed back into the culture media.…”

Ecological Approaches to Dental Caries Prevention: Paradigm Shift or Shibboleth?

“…One of the problems identified in using probiotics for caries prevention is that the commonly available Lactobacillus and Bifidobacterium probiotic bacteria are themselves acidogenic and aciduric, and could contribute to the caries process if such bacteria are allowed to colonize the oral cavity [Maltz and Beighton, 2012]. Recent in vitro biofilm studies have confirmed this apprehension with different strains such as Lactobacillus salivarius W24 [Pham et al, 2009], Lactobacillus rhamnosus GG [Schwendicke et al, 2014a], Bifidobacteria animalis lactis BB12 [Schwendicke et al, 2014b], Lactobacillus rhamnosus LB21 [Fernández et al, 2015], and Lactobacillus acidophilus LA-5 [Schwendicke et al, 2017] which have all been shown to lower biofilm pH. In fact, some Lactobacillus and Bifidobacterium strains have greater cariogenic attributes than even MS [Beighton et al, 2010].…”

Antagonistic effects ofStreptococcusandLactobacillusprobiotics in pharyngeal biofilms

“…In this context, a strain of Streptococcus salivarius K12 is marketed for oral (Fernandez et al . ) and oropharyngeal use, and has shown promise in the prevention and management of bacterial pharyngitis in children and adults (Tagg ; Di Pierro et al . , , ) and in limiting group B Streptococcus colonization of the vagina in mice (Patras et al .…”