Effects of Lactobacillus spp. isolated from oral cavity of caries-free subjects on Streptococcus mutans: study of probiotic activity

Abstract

The idea of using micro-organisms from the resident microbiota to inhibit the growth of pathogenic bacteria was proposed over a century ago and today assists on the development of new therapeutic strategies for infections. Previous studies corroborated that probiotic strains Lactobacillus can inhibit Streptococcus mutans, however the effects of Lactobacillus on the formation of biofilms and caries development need to be investigated. The objective of this study will evaluate the effect of Lactobacillus strains isolated from caries-free subjects on S. mutans using study models in vitro and in vivo. On the in vitro study, 30 Lactobacillus strains isolated from the oral cavity of caries-free subjects will be evaluated for antibacterial activity against S. mutans in planktonic growth. Hereafter 10 strains that exhibit higher antibacterial activity will be selected for the study of antimicrobial effects on biofilms of S. mutans formed on hydroxyapatite discs. In all these tests in addition to the effects of Lactobacillus strains on S. mutans will also be evaluated the effects of the filtrated culture of Lactobacillus on S. mutans checking the inhibitory effects related to the acid environment and antimicrobial substances secreted by Lactobacillus. For in vivo study, one Lactobacillus strain will be selected with higher inhibitory effect on biofilm of S. mutans to assess its effects on the development of experimental caries in rats. After infection by S. mutans and Lactobacillus strain in the oral cavity of the rats, sampling of biofilm will be conducted to count CFU/mL and analysis of the maxilla and mandible in stereomicroscope for quantification of occlusal caries and smooth surface will be performed. The results will be submitted to an exploratory analysis for selecting the most appropriate statistical test for each experiment of this study. (AU)