Alkali- and Acid-producing Bacteria Associated with Caries and Health

Objective:  To compare the proportions of selected alkali-producing and acid-producing bacteria in dental plaque from children with respect to caries status and urease activity.

Methods:  DNA was extracted from 12 plaque samples with high urease activity (HU: mean 10.17 µmoles urea min^-1 (mg protein)^-1 and 10 samples with low urease activity (LU: mean 1.91 µmoles urea min^-1 (mg protein)^-1.  Of the HU plaques, eight came from caries-free (CF), and four from caries-active (CA) children.  Of the LU samples, four came from CF, and six from CA children.  Samples were analyzed by real-time PCR using primers specific for the ureA gene of Actinomyces naeslundii, the arcA gene of Streptococcus gordonii, and the gtfB gene of Streptococcus mutans.  The copy number of each gene was normalized to that of 16S rDNA for total bacteria.  The proportions of each species were compared with respect to a: urease activity b: caries status and c: urease activity and caries status together using the Kruskal-Wallis non-parametric test.

Results: HU samples contained higher proportions of A. naeslundii and S. gordonii compared to LU plaques, however this difference was not statistically significant (P>0.05).  Plaques from CF children had higher proportions of A. naeslundii and lower proportions of S. mutans compared to CA ones (P=0.021).  When samples were stratified according to both urease and caries, HU/CF plaques had higher proportions of A. naeslundii and S. gordoni and lower proportions of S. mutans (P<0.001 for S. mutans) compared to the LU/CA samples.

Conclusions:  Increased cariogenic activity in the dental plaque of children may be related not only to increased proportions of acidogenic bacteria, but also to a loss of bacteria that are able to generate alkali from urea and arginine.  Analysis of a larger number of samples is necessary to confirm the later observations statistically.

Supported by P20RR11126, DE015285, DE10362, G12RR03051.