Proteolytic Activity of Upon κ-Casein Undermines Its "Caries-Safe" Effect

Milk is believed to be a relatively "caries-safe" food. This belief relies on the fact that caseins, which constitute around 80% of milk's protein content, were found to inhibit the adhesion of to enamel and, therefore, decrease biofilm formation. While is considered a leading cause of dental disorders, is a non-pathogenic foodborne bacterium, frequently contaminating milk and its products. This study aimed to investigate the effects of dairy-associated foodborne bacteria such as on biofilm formation by in the presence of casein proteins. Our results indicate that there is a significant decrease in total biofilm formation by exposed to a casein protein mixture in a mono-species culture, whereas, in the co-culture with , an inhibitory effect of the caseins mixture on biofilm formation was observed. Proteolytic activity analysis suggested that is capable of breaking down milk proteins, especially κ-casein, which enables biofilm formation by in the presence of milk caseins. Therefore, these findings may challenge the assumption that milk is "caries-safe", especially in a complex microbial environment.