Urease and Dental Plaque Microbial Profiles in Children

<div><p>Objective</p><p>Urease enzymes produced by oral bacteria generate ammonia, which can have a significant impact on the oral ecology and, consequently, on oral health. To evaluate the relationship of urease with dental plaque microbial profiles in children as it relates to dental caries, and to identify the main contributors to this activity.</p><p>Methods</p><p>82 supragingival plaque samples were collected from 44 children at baseline and one year later, as part of a longitudinal study on urease and caries in children. DNA was extracted; the V3–V5 region of the 16S rRNA gene was amplified and sequenced using 454 pyrosequencing. Urease activity was measured using a spectrophotometric assay. Data were analyzed with Qiime.</p><p>Results</p><p>Plaque urease activity was significantly associated with the composition of the microbial communities of the dental plaque (Baseline P = 0.027, One Year P = 0.012). The bacterial taxa whose proportion in dental plaque exhibited significant variation by plaque urease levels in both visits were the family Pasteurellaceae (Baseline P<0.001; One Year P = 0.0148), especially <i>Haemophilus parainfluenzae</i>. No association was observed between these bacteria and dental caries. Bacteria in the genus Leptotrichia were negatively associated with urease and positively associated with dental caries (Bonferroni P<0.001).</p><p>Conclusions</p><p>Alkali production by urease enzymes primarily from species in the family Pasteurellaceae can be an important ecological determinant in children’s dental plaque. Further studies are needed to establish the role of urease-associated bacteria in the acid/base homeostasis of the dental plaque, and in the development and prediction of dental caries in children.</p></div

Heatmap and assigned taxonomy of the most representative OTUs (minimum 500 copies) in dental plaque samples at baseline (A) and one year later (B).

<p>Samples are arranged by increasing plaque urease levels (left: lowest, to right: highest). * indicates OTUs that exhibit significant difference among samples with urease below the median vs. those with urease levels above the median (Bonferroni P<0.001).</p

OTUs whose frequencies in dental plaque of children differ significantly^* by: A) plaque urease (above median vs. below median), B) caries experience (dmfs>0 vs. dmfs = 0), and C) active dentine caries (dentine caries present vs. no dentine caries).

<p>* g-test with Bonferroni correction for multiple comparisons P<0.001.</p><p>Taxonomic classification of the OTUs into species was performed by BLAST against the HOMD.</p

Bacterial taxon summary at Family level for dental plaque samples by plaque urease activity at Baseline and One Year later.

<p>*indicates a significant difference in the variance of the bacterial family among the different urease categories after multiple comparisons (ANOVA P<0.05, Bonferroni P<0.05). ·ANOVA P<0.05, Bonferroni P>0.05).</p

Principal Coordinate Analysis of bacterial communities in Baseline samples of dental plaque from children by plaque urease activity and caries status.

<p>Figures A, B and C: samples divided by median urease activity: red- below the median (<2.65 units/mg); green- above the median (>2.65 units/mg). Figures D, E, and F: red- lowest urease quartile (<1.72 units/mg) vs. bleu- highest urease quartile (>4.0 units/mg); light gray: second and third quartile of urease (1.72–4.0 units/mg). A and D: All samples; B and E: Caries-Free (dmfs = 0); C and F: Caries-Experienced (dmfs>0). Circled samples in the Caries-Free groups belong to children who were initially caries free but developed caries within the one-year study period. In the Caries-Experienced group, the circled samples correspond to children who had previous caries but did not develop any new lesions within the one-year study period.</p

Principal Coordinate Analysis of bacterial communities in One-Year samples of dental plaque from children by plaque urease activity and caries status.

<p>Figures A, B and C: samples divided by median urease activity: red- below the median (<2.16 units/mg); green- above the median (>2.16 units/mg). Figures D, E, and F: red- lowest urease quartile (<1.62 units/mg) vs. bleu- highest urease quartile (>2.86 units/mg); light gray: second and third quartile of urease (1.62–2.86 units/mg). A and D: All samples; B and E: Caries-Free (dmfs = 0); C and F: Caries-Experienced (dmfs>0). Circled samples in the Caries-Free groups belong to children who were initially caries free but developed caries within the one-year study period. In the Caries-Experienced group, the circled samples correspond to children who had previous caries but did not develop any new lesions within the one-year study period.</p