An in vitro investigation of Lactococcus lactis antagonizing cariogenic bacterium Streptococcus mutans

Objectives: The present study tested the antagonism between Lactococcus lactis and Streptococcus mutans and evaluated the feasibility of the application of L. lactis for the inhibition of S. mutans in the oral cavity. Methods: Competition assays on plates were employed to determine whether L. lactis antagonises S. mutans under different nutritional conditions, and real-time reverse-transcriptase PCR was used to evaluate the effects of metabolites of S. mutans on the bacteriocin nisin genes in L. lactis. Furthermore, the colonisation and effects of L. lactis on the surface of a tooth were examined by scanning electron microscopy. Results: L. lactis competitively inhibited S. mutans growth under nutritional deficiency, and the metabolites of S. mutans, including several exogenous molecular signals, enhanced the expression of genes related to nisin synthesis, nisA, nisB and nisI. Additionally, L. lactis effectively colonised the surface of tooth enamel, which showed substantially less decay with L. lactis adhesion compared to S. mutans adhesion. Conclusions: These findings suggest avenues of research into a new strategy to reduce major cariogenic S. mutans adhesion on the surfaces of teeth. (C) 2011 Elsevier Ltd. All rights reserved.