Molecular sequencing of collagen-binding adhesin genes in Streptococcus mutans isolated from patients with severe dental caries in Iraq

Document Type : Research Paper

Authors

Department of Microbiology, College of Medicine, University of Babylon, Hilla, Iraq.

Abstract

Objective
One of the most important bacteria causing dental caries is Streptococcus mutans. This agent is known as the main etiological agent of dental caries. The pathogenicity of this bacterium is closely related to collagen-binding adhesins and cell surface-associated proteins. This bacterium also has a high ability to adhere to dental surfaces, form resistant biofilms, produce acid through carbohydrate fermentation, and survive in acidic conditions. This increases the pathogenicity of this bacterium. The aim of this study was to investigate and identify the sequences of WapA, SpaP, Cnm, and Cbm genes in Streptococcus mutans Iraqi isolates, compare these sequences with international reference strains, and evaluate the phylogenetic relationships between them.
Materials and methods
A total of 138 oral swab samples were collected from patients with severe dental caries, including those with and without type 1 diabetes mellitus. 32 control samples were also prepared from healthy individuals without dental caries. Sampling was performed at the Health Education Center and Specialized Dental Center in Babylon Province, Iraq. Oral swabs were collected from patients with severe dental caries in two subgroups, those with and without type 1 diabetes, and from healthy individuals. Streptococcus mutans isolates were then isolated and genomic DNA was extracted. The genes of interest were amplified by PCR and sequenced. Reference sequences in the GenBank database were used to perform sequence alignment and BLAST analyses. Phylogenetic trees were drawn and analyzed to assess the evolutionary relationships between isolates and reference strains.
Results
Sequencing results showed that for all four genes studied, there was 99-100% similarity between local isolates and global reference strains. A limited number of substitution mutations were identified in the WapA and SpaP genes. However, no sequence changes were observed in the Cnm and Cbm genes. This indicates that the Cnm and Cbm genes are completely conserved. The results of phylogenetic analyses showed that the cluster of Iraqi isolates is close to the clusters of international pathogenic strains. This could indicate high genetic similarity and close evolutionary relationships between them.
Conclusion
These findings indicate high genetic conservation of adhesion genes in Streptococcus mutans among different populations and at the same time indicate the existence of microevolutionary variations that could contribute to strain-specific pathogenicity. Gene sequencing is recognized as an important tool in monitoring the evolution of pathogenicity and can play an effective role in guiding preventive strategies for oral health and controlling dental caries.

Keywords

References

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Agricultural Biotechnology Journal
Volume 18, Issue 1
January 2026
Pages 301-318

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