Raman signatures of Cnm-positive Streptococcus mutans: II, screening the virulence of clinical isolates

This study dealt with developing a Raman spectroscopic method for estimating the degree of virulence of Streptococcus mutans bacteria isolated from clinical swab samples. Raman experiments aimed at establishing suitable spectroscopic parameters to quantify bacterial virulence and were conducted on a limited series of six clinical isolates three of which were genomically classified as Cnm-positive and three as Cnm-negative. Samples were characterized after biofilm purification and compared with cultures of the same bacteria in physiological state of equilibrium, namely, after long-term stabilization in vitro. Statistically significant series of ten Raman spectra were collected at different locations on each clinical sample, and their averages interpreted as multiomic snapshots of bacterial structure. Building upon the spectroscopic analyses described in the companion paper Part I, Raman characterizations of clinical isolates revealed a significant degree of variability in the bacterial structure, but also suggested clear classification criteria for clinical samples. These spectroscopic criteria reflected specific biochemical circumstances affecting the structure of bacteria in their pathophysiological state. Raman algorithms based on the fractional balance between proteins and peptidoglycans, and the degree of protein structural disorder vs. presence of oxysulfur compounds enabled insightful classifications of bacterial virulence, which matched genomic analyses. These structural characteristics, which allowed distinguishing between Cnm-positive and Cnm-negative bacteria, could provide fast and unbiased diagnostic criteria for risk assessments of endocarditis and hemorrhagic strokes as induced by Cnm-positive bacteria. In summary, the present study proposes a new spectroscopic approach to oral flora-related diagnostics and confirms the potential utility of Raman spectroscopy in chairside analyses of clinical isolates.