As dental caries develop, oral biofilms experience shifts in both microbial makeup and phenotypic behavior. This investigation aimed to assess and compare the acid tolerance (AT) of dental plaque collected from two cohorts of children—one group presenting with severe caries (CA) and another entirely caries-free (CF)—and to link these findings with variations in microbial composition and metabolic activity within the biofilms.
Plaque was obtained from 20 children aged 2–5 years in each cohort. Acid tolerance was determined by measuring bacterial viability after an acid exposure at pH 3.5, employing LIVE/DEAD® BacLight™ staining combined with confocal microscopy. AT was scored on a scale from 1 (minimal/no tolerance) to 5 (extensive tolerance). Metabolic end-products following a 20 mM glucose challenge for one hour were analyzed through Nuclear Magnetic Resonance (NMR). Microbial community profiles were generated using 16S rRNA Illumina sequencing. The CA group showed a markedly higher mean AT score (4.1) compared to the CF group (2.6, p < 0.05). Post–glucose pulse, CA plaques exhibited significantly elevated ratios of lactate to acetate, lactate to formate, lactate to succinate, and lactate to ethanol relative to CF samples (p < 0.05). Sequencing data identified 25 species enriched in CA plaque, among them taxa from Streptococcus, Prevotella, Leptotrichia, and Veillonella (p < 0.05).These findings indicate that pooled plaque from children with extensive caries displays an increased AT when compared with plaque from healthy peers, and that this characteristic aligns with differences in microbial activity and community composition. Consequently, the collective functional phenotype of plaque may serve as a potential marker for caries status. However, longitudinal research is required to determine whether shifts in AT over time can reliably forecast caries development before AT can be applied as a predictive clinical indicator.
