Genetic polymorphisms of the sortase A gene and early childhood caries in two-year-old children

Genotypic diversity of Streptococcus mutans in children with and without early childhood caries- A systematic review

OBJECTIVE

Genotypic diversity and polymorphism of Streptococcus mutans remain as a topic of interest, as this provides a satisfactory explanation for the contrasting caries status in people harboring Sterptococcus mutans. This systematic review aimed to analyze and appraise Genomic diversity of Streptococcus mutans and its relationship in Early Childhood Caries.

METHODS

A literature search was conducted until August 2020 using PubMed, Cochrane central, SIGLE using search keywords and MeSH headings include "Early Childhood caries", "Streptococcus mutans" and "Genotypic diversity". Apart from the aforementioned electric search, manual search was also done. The retrieved papers were assessed by three review authors and the disagreements were discussed and the final decision was made by consensus. Qualities of the included studies were assessed and data were extracted for analysis.

RESULTS

A total of 4081 papers were retrieved for screening after the removal of duplicate articles. Among the retrieved studies, 4074 papers did not satisfy the study inclusion criteria. Finally, those 7 papers which fulfilled all the inclusion criteria were selected and reviewed systematically.

CONCLUSION

Genetic polymorphism and genetic mutation exist in S.mutans strain and the missense mutation varies between children with and without Early Childhood caries. The number of genotypes of S.mutans varies between caries active and caries-free children. Due to the lack of adequate studies on gene mutations for direct comparison, further studies are needed to evaluate these gene mutation and its diversities to draw a definitive conclusion.

Effects of missense mutations in sortase A gene on enzyme activity in Streptococcus mutans

Background

Streptococcus mutans (S. mutans) is the major aetiological agent of dental caries, and the transpeptidase Sortase A (SrtA) plays a major role in cariogenicity. The T168G and G470A missense mutations in the srtA gene may be linked to caries susceptibility, as demonstrated in our previous studies. This study aimed to investigate the effects of these missense mutations of the srtA gene on SrtA enzyme activity in S. mutans.

Methods

The point mutated recombinant S.mutans T168G and G470A sortases were expressed in expression plasmid pET32a. S. mutans UA159 sortase coding gene srtA was used as the template for point mutation. Enzymatic activity was assessed by quantifying increases in the fluorescence intensity generated when a substrate Dabcyl-QALPNTGEE-Edans was cleaved by SrtA. The kinetic constants were calculated based on the curve fit for the Michaelis-Menten equation.

Results

SrtA_{△N40(UA159)} and the mutant enzymes, SrtA_△N40(D56E) and SrtA_{△N40(R157H)}, were expressed and purified. A kinetic analysis showed that the affinity of SrtA_△N40(D56E) and SrtA_{△N40(R157H)} remained approximately equal to the affinity of SrtA_{△N40(UA159)}, as determined by the Michaelis constant (K_m). However, the catalytic rate constant (k_cat) and catalytic efficiency (k_cat/K_m) of SrtA_△N40(D56E) were reduced compared with those of SrtA_{△N40(R157H)} and SrtA_{△N40(UA159)}, whereas the k_cat and k_cat/K_m values of SrtA_{△N40(R157H)} were slightly lower than those of SrtA_{△N40(UA159)}.

Conclusions

The findings of this study indicate that the T168G missense mutation of the srtA gene results in a significant reduction in enzymatic activity compared with S. mutans UA159, suggesting that the T168G missense mutation of the srtA gene may be related to low cariogenicity.

Electronic supplementary material

The online version of this article (doi:10.1186/s12903-016-0204-1) contains supplementary material, which is available to authorized users.

Genetic polymorphisms of the sortase A gene and social-behavioural factors associated with caries in children: a case-control study

Background

Streptococcus mutans (S. mutans) is the primary etiological agent of dental caries. Sortase is a transpeptidase that anchors several surface proteins to the S. mutans cell wall and has been shown to play a major role in cariogenicity. The purpose of this study was to explore the genetic polymorphisms of the sortase gene (srtA) and the social-behavioural factors associated with dental caries in children with S. mutans.

Methods

In this case–control study, 121 S. mutans strains were separately selected from caries-free children and high-severity caries children for sequencing of the srtA gene. Social and behavioural data were collected by self-administered questionnaires. Genomic DNA was extracted from S. mutans strains and amplified by PCR to obtain the srtA gene. The purified PCR products were sequenced and analysed for mutations with ABI Variant Reporter software. The distribution of missense mutations and the mean of social-behavioural factors were compared between the groups. A multiple logistic regression model was used to control for confounding factors.

Results

The mutation frequencies at loci 168 (P = 0.023) and 470 (P = 0.032) were significantly different between the groups. The best-fitting model showed that greater age, high frequencies of solid sugar consumption, prolonged breastfeeding, a high proportion of visible plaque, and S. mutans with a T at locus 168 of the srtA gene were associated with high-severity caries in children (P < 0.05). Children carrying a G at locus 168 of S. mutans had a decreased risk for high-severity caries (OR = 0.32, 95% CI = 0.12–0.86) compared with those carrying a T.

Conclusions

The present study suggested that the locus 168 missense mutation of the srtA gene may correlate with caries susceptibility in children with S. mutans. In addition, age, duration of breastfeeding, solid sugar consumption, and poor oral hygiene contributed to this complex disease.