Variability of the SPA-P gene as a potential biomarker of Streptococcus Mutans virulence in childhood caries

Abstract

Objective: To evaluate the associations between S. mutans spa-P gene haplotypes, bacterial load (CFU/mL), the Oral Hygiene Index (OHI), caries experience (dmft+DMFT), and the caries component (d+D) in children.

Methods: A total of 51 patients were included in the study. DNA was extracted from S. mutans strains isolated from stimulated saliva, and the spa-P gene was sequenced. A descriptive analysis of the clinical, microbiological, and genetic variables was conducted. Generalized linear models were used to assess the association between the dmft+DMFT, d+D, OHI, and CFU/mL >10⁴ indices and S. mutans haplotypes, with results expressed as incidence rate ratios (IRR) and 95% CI. The associations were validated using Fisher’s exact test

Results: The mean dmft+DMFT value was 6.35 ± 4.79. Thirty haplotypes of the spa-P gene were identified, with haplotype 4 being the most common, shared by strains from 9 children. No significant associations were detected between the haplotypes of the spa-P gene and CFU/mL (p = 0.225), dmft+DMFT (p = 0.833), or d+D (p = 0.294). CFU/mL levels were positively but not significantly associated with higher dmft+DMFT values (IRR=1.34; 95% CI: 0.732–2.42) and a higher caries component score (IRR=1.32; 95% CI: 0.66–2.57). The d+D component was more strongly associated with the OHI (IRR = 2.17; 95% CI 1.11–4.22; p < 0.05).

Conclusions: The results revealed a high genetic diversity of the spa-P gene in S. mutans, with no significant associations observed with caries experience or CFU/mL levels. Furthermore, the influence of the d+D component is highlighted, as it shows a significant correlation with the oral hygiene index.