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 Streptococcus mutans to enamel and, therefore, decrease biofilm formation. While S. mutans is considered a leading cause of dental disorders, Bacillus subtilis 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 B. subtilis on biofilm formation by S. mutans in the presence of casein proteins. Our results indicate that there is a significant decrease in total biofilm formation by S. mutans exposed to a casein protein mixture in a mono-species culture, whereas, in the co-culture with B. subtilis, an inhibitory effect of the caseins mixture on S. mutans biofilm formation was observed. Proteolytic activity analysis suggested that B. subtilis is capable of breaking down milk proteins, especially κ-casein, which enables biofilm formation by S. mutans in the presence of milk caseins. Therefore, these findings may challenge the assumption that milk is “caries-safe”, especially in a complex microbial environment.
Bibliographical noteFunding Information:
Acknowledgments: This study forms part of Danielle Duanis-Assaf’s Ph.D. project and Eli Kenan’s DMD project. Danielle Duanis-Assaf is a recipient of the Scholarship of Excellency for outstanding Ph.D. students from the ARO and STEP-GTP sisters fellowship.
© 2020 by the authors. Licensee MDPI, Basel, Switzerland.
- Bacillus subtilis
- Biofilm formation
- Milk caseins
- Streptococcus mutans