Method: The effect of lactose was tested on S. mutans UA159 in planktonic and biofilm conditions. For planktonic growth, S. mutans were grown overnight at 37ºC in BHI supplemented with different concentrations of lactose (1-5% (w/v)) or galactose (1-3% (w/v)). Changes in pH and growth (OD, λ=595nm) were recorded during incubation. Additionally, the biofilm of S. mutans was generated in BHI with/without 2% (w/v final) sucrose. Biofilm biomass was quantified by crystal violet (CV) staining and qPCR using species specific primers for the gene encoding for 16S rRNA. Biofilm depths, vitality and extracellular polysaccharides (EPS) were examined using CLSM. Biofilm related genes were examined using reverse transcription and qPCR.
Result: The addition of lactose and galactose did not show any significant effect on S. mutans growth in all tested concentrations. Importantly, lactose had the same acidogenic effect in all tested concentrations. The CV and qPCR methods showed a significant increase (about 100%) of biofilm biomass in the presence of lactose or galactose, in comparison to control. Further, the type of EPS produced by S. mutans in with the presence of lactose appears to be different compared to the polysaccharides produced in with the presence of sucrose. Finally, genes previously found to be related to biofilm formation of S. mutans were significantly up-regulated in the presence of lactose.
Conclusion: Our results suggest that lactose and galactose notably enhances S. mutans' ability to form biofilm and adds new insights to our understanding of effect of the predominant sugars of milk on dental biofilm development.