Salivary gel-forming mucin MUC5B--a nutrient for dental plaque bacteria.

INTRODUCTION: Model systems with oral bacteria from dental plaque have demonstrated that the utilization of complex glycoproteins as a food source cannot be undertaken by single species but requires concerted degradation by a multi-species consortium, with each member contributing one or a few hydrolytic enzymes. Unlike previous studies, the aim of the present investigation was to explore the ability of fresh dental plaque to degrade salivary mucin, MUC5B, isolated by methods designed to retain intact the natural polymeric structure and physiological conformation, in an attempt to mimic the naturally occurring interaction between the oral microbiota and salivary mucins.
METHODS: Human salivary MUC5B was isolated from whole saliva by density-gradient centrifugation and incubated with freshly isolated supragingival dental plaque with samples subjected to fluorescent staining for viability and metabolic activity. In addition, the degradation of MUC5B oligosaccharide side chains was studied using a lectin assay, recognizing three different carbohydrate epitopes commonly found on mucin oligosaccharide side chains.
RESULTS: The addition of purified salivary MUC5B elicited a strong metabolic response from the biofilm cells, whereas individual strains of Streptococcus oralis and Streptococcus gordonii isolated from the same plaque were not able to utilize the MUC5B. The degradation of terminal saccharide moieties on the MUC5B was demonstrated by a marked decrease in both sialic acid and fucose reactivity.
CONCLUSION: These results have shown that dental plaque is capable of utilizing human salivary MUC5B as a nutrient source, a process possibly requiring the synergistic degradation of the molecule by a consortium of oral bacteria in the plaque community.