Abstract
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.
Highlights
Milk is a complex colloidal mixture of proteins, fats, sugars, and minerals, with some in suspension and some in solution [1]
The first step in this study was to determine the effect of the major milk caseins on the surface attachment and biofilm formation by S. mutans
It was found that the biofilm biomass was reduced by 30% following the addition of casein protein mixture at a concentration of 0.5%, with a decrease of up to 94% with the addition of 1.5% casein
Summary
Milk is a complex colloidal mixture of proteins, fats, sugars, and minerals, with some in suspension and some in solution [1]. Milk provides all the necessary energy and nutrients to ensure proper growth and development; it is crucial with respect to bone mass formation, as well as the prevention of several chronic conditions such as cardiovascular diseases, some forms of cancer, obesity, and diabetes [4]. Caries is the most common chronic infectious disease related to the oral cavity [5]. Different sophisticated mechanisms of adherence account for the distribution of different species to a particular habitat in the oral tissues [7]. In addition to the adherence properties, dental biofilm displays a complex structure due to the extracellular matrix, which contributes to its resistance to mechanical removal, constitutes a reservoir for nutrients and bacteria, and determines the interactions of the biofilm with the environment [5]
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