Lactose triggers biofilm formation by Streptococcus mutans

The most cariogenic bacterium, Streptococcus mutans, often adopts a sessile lifestyle in response to carbohydrates. Biofilm formation represents one of the most successful strategies for survival by S. mutans in a dental environment. This study reports induced biofilm formation by S. mutans in the presence of lactose, the primary sugar in milk. Importantly, no major difference was observed in S. mutans growth in the presence of different concentrations of lactose in growth medium, indicating that lactose has a specific effect on biofilm formation. Moreover, extracellular polysaccharides produced by S. mutans in response to lactose were found to be different from the polysaccharides produced in the presence of sucrose. It is further reported that several biofilm-related genes of S. mutans were significantly up-regulated in response to lactose. These results lead to the conclusion that lactose may promote biofilm formation by S. mutans, the most important bacterium involved in dental diseases.