Raman signatures of Cnm-positive Streptococcus mutans: I, the molecular origin of cerebral microbleeds

This study featured a Raman spectroscopic analysis aimed at unfolding structural differences at the molecular scale between Cnm -positive and Cnm -negative Streptococcus mutans bacteria and their respective biofilms. The primary goal of this analysis was to unveil the molecular origin of enhanced virulence and propensity to damage endothelial tissue of strains containing the Cnm gene. In situ Raman assessments of live biofilm exopolysaccharides, generated upon sucrose addition by Cnm -positive and negative cultures, revealed additional features that linked to specific metabolic characteristics. The Raman spectra of Cnm -positive and Cnm -negative bacterial cells were strikingly different. In the Cnm -positive strain, strong signals from a variety of residual oxysulfur molecules, including indoxyl and other sulfates (likely stored in the Cnm protein at the bacterial surface), suggested that this strain is capable to exploit sulfur chemistry for anchoring purposes, while simplifying the structure of its peptidoglycan membrane. On the other hand, the Cnm -positive strain appeared to have conspicuously lost its capacity of producing and storing glycogen molecules, possibly allocating differently its resources in adaptive advantage for tissue invasive activity. Regarding biofilm structure, the Cnm -positive strain produced larger amounts of glucans for a lesser number of cells; however, the ratio between α -1,6- and α-1,3-glucan fractions showed no significant variations in comparison to the Cnm -negative strain, suggesting that adhesion rather than biofilm strength and impermeability is the main priority in its overall functionality.