PCR-Based investigation of virulence genes in Streptococcus sobrinus isolated from dental caries

Objective: Streptococcus sobrinus is a highly cariogenic, acidogenic, and strong biofilm-forming species. This may be the initial study to report the prevalence of eno1, atl, and S1 serine protease genes in S. sobrinus from Iraqi patients. Methods: Carious tooth samples were obtained from patients between 6 and 60 years. Bacteria were isolated by conventional culture methods and were characterised by Gram staining, colony morphology, and biochemical properties. Twenty S. sobrinus isolates were additionally tested by PCR using primers specific for eno1 atl, and s1 family serine protease. The PCR products were examined by agarose gel electrophoresis. Results: Bacterial growth was observed in 90 (81%) of the 110 samples. S. sobrinus was the most common (22.2%), followed by Lactobacillus spp., Enterococcus spp., Fusobacterium spp., and other species. The S. sobrinus isolates were Gram-positive, catalase-positive, non-motile, with sticky mucoid colonies. The eno1 gene was present in 7 of the 20 isolates (35%) as determined by PCR, indicating strain variation in distribution. The atl gene was present in 17 isolates (85%), and the S1 family serine protease gene, which was present in all the tested isolates (20; 100%), was conserved. Conclusion: This research emphasises the prevalence of S. sobrinus in carious lesions and the variation of virulence gene distribution. The ubiquitous presence of S1 protease and the high incidence of atl suggest that they are fundamental to pathogenicity, although the presence of a percentage of eno1 implies genetic diversity. Identified virulence genes may guide early diagnostics and targeted preventive strategies for dental caries.