The in-vitro effect of bovine milk, and plant-based alternatives on oral microorganisms and biofilms

This in vitro study aimed to evaluate the effects of bovine milk and plant-based alternatives on oral microorganisms and multispecies biofilms, in part in interaction with monocytic cells. Test substances (all without added sugar) included bovine milk, plant-based oat drink, plant-based almond drink, and plant-based soy drink. Growth of Streptococcus gordonii, S. mutans (here also with 7.5% sucrose), and Porphyromonas gingivalis with 2.5% and 10% test substances was measured. Sediment of P. gingivalis cultures with 10% test substance at 24 h was assayed for Arg-gingipain activity. Further, two defined multi-species biofilms (caries and periodontal) were cultured on surfaces coated with the test substances (final concentration 10%) for 4 h and 24 h or 48 h, before biofilms were analyzed. Monocytic cells were added to periodontal biofilm, and thereafter, interleukin (IL)-1β and IL-10 expression was determined. The growth of S. gordonii was slightly promoted by bovine milk and by three of the four plant-based milk alternatives tested. In media with 5% sucrose and test substances, the S. mutans colony forming units (CFU) counts were lower at 6 h with the lowest counts after incubation with 2.5% bovine milk. Almond drink reduced the CFU counts in a formed cariogenic biofilm; bovine milk and soy drink reduced both mass and metabolic activity. The arginine-specific amidolytic activity of P. gingivalis was blocked with 10% almond drink. Oat drink and bovine milk decreased both CFU counts and metabolic activity of the formed periodontal biofilm. Independent of biofilm presence, soy drink increased the release of IL-10. These in-vitro results may support the available epidemiologic data on the inverse association of the intake of milk with caries and periodontitis. Plant-based drinks should be further investigated. Of special interest might be the inhibition of gingipain activity by almond drink as well as the immune-modulatory effects of soy drink.