Ureolytic bacteria in dental plaque and caries progression in children

Bacterial urease enzymes hydrolyze salivary urea and generate alkali in the oral cavity.  A recent longitudinal study showed that urease activity in plaque was associated with reduced caries risk in children over a three-year study period; however, increased urease activity in saliva was significantly associated with increased caries risk.

Objective: The objective of this study was to evaluate the relationship of ureolytic oral bacteria with dental caries in children over a three-year period.

Methods:   140 plaque samples collected from 20 children over a three-year period were selected from a larger longitudinal study on the basis of the variability in urease activity levels observed during the study period.  The samples were analyzed by qPCR using gene specific primers for two ureolytic species (Actinomyces naeslundii and Streptococcus salivarius), two arginolytic species (Streptococcus sanguis and Streptococcus gordonii), and Streptococcus mutans.  Generalized latent linear and mixed models were used to study the relationship of these bacteria with three caries outcomes: enamel caries, dentin caries, and dmfs, adjusted for age, gender, and baseline caries.

Results:  A. naeslundii was negatively associated with enamel caries (adj.β=-0.03, P=0.001).  S. salivarius , which is a predominant ureolytic species in saliva and which is found only in very small numbers in plaque was positively associated with dentin caries (adj.β=3.44, P=0.012) and with the dmfs (adj.b=2.69, P=0.024).  S. sanguis (adj.β=0.05, P=0.015) and S. gordonii (adj.β=0.04, P=0.015) were positively associated with enamel caries, while S. mutans was positively associated with the advanced lesions (adj.β=2.54, P=0.031).

Conclusion: The results from the microbiological analysis are in agreement with the biochemical findings of this prospective study with respect to the relationship of urease with caries development in children.  A more thorough microbiological analysis using novel and more powerful technologies will help further dissect this complex relationship.

Grant Support: K23 DE015285, G12 RR 0305, U54RR026139-01A1