Streptococcus mutans membrane lipid composition: Virulence factors and structural parameters

Objective: The aim of the present work was to analyze whether the location of the dental biofilm was associated with shifts in the membrane fatty acid profile, and whether such shifts could affect certain virulence factors of strains of Streptococcus mutans. Design: An experimental study was conducted to assess the behavior of S. mutans strains isolated from dental biofilm collected from sound and carious smooth and occlusal surfaces of the oral cavity of children. The lipid composition of the bacterial membrane, structural membrane parameters, acid survival, and ATPase activity were tested at pH 7 and 5. Results: At pH 5, an increase in both the unsaturated and the long chain fatty acids as well as in proton ATPase hydrolytic activity was observed in strains isolated from carious smooth surface biofilm but not in carious occlusal surface strains. The observed changes correlated with the studied structural parameters, and were found to be associated with membrane organization. The changes correlated with a decreased in Delta C (sn-1 and sn-2 acyl chain inequivalence), indicative of increased acyl chain interaction. Conclusions: The obtained results suggest that the acidic environment (pH 5) of smooth surface caries affects membrane organization, inducing a shift in membrane lipid profile, which would likely induce better protein/lipid hydrophobic matching, resulting in increased ATPase activity and higher acid survival.