Association between biofilm-related genes and phenotypic formation capacity in Streptococcus mutans isolated from the oral cavity

Abstract

Objective: To investigate the relationship between the presence of four key biofilm-associated genes (gtfB, gbpA, comDE, atpH) and phenotypic biofilm formation capacity in clinical oral isolates of Streptococcus mutans.

Methods: Three hundred clinical samples (saliva, dental plaque, and dental caries specimens) were collected from patients attending dental clinics in Nasiriyah, Iraq, between November 2025 and February 2026. S. mutans was isolated using selective media and identified by biochemical tests and 16S rRNA PCR. Biofilm formation capacity was assessed using the microtiter plate method. PCR was employed to detect the presence of gtfB, gbpA, comDE, and atpH genes. Statistical analysis was performed using Fisher's exact test.

Results: Thirty-six (12%) isolates were confirmed as S. mutans. Phenotypically, 31 isolates (86.1%) produced biofilms: 11 (30.5%) strong, 9 (25%) moderate, and 11 (30.5%) weak biofilm formers. Genotypically, gtfB was present in all 36 isolates (100%), while comDE, atpH, and gbpA were found in 35 (97.2%), 34 (94.4%), and 31 (86.1%) isolates, respectively. No statistically significant association was observed between the presence of any tested gene and biofilm formation strength (p > 0.05 for all comparisons).

Conclusion: Biofilm-associated genes are highly prevalent among oral S. mutans isolates, yet their mere presence does not predict phenotypic biofilm strength. This discrepancy suggests that post-transcriptional regulation, allelic variations, or alternative pathways critically modulate biofilm formation.