Relative stability of Streptococcus mutans gtfB expression following short-term probiotic exposure in mouth-breathing children: a pilot study

Background Mouth-breathing induces alterations in the oral environment that may promote microbial dysbiosis. Streptococcus mutans is a major cariogenic bacterium associated with mouth-breathing conditions, with the gtfB gene representing a key virulence determinant involved in bacterial pathogenicity. However, the molecular response of virulence gene expression under altered respiratory conditions remains insufficiently understood. Objective This pilot study aimed to investigate the relative stability of gtfB gene expression following short-term probiotic exposure in mouth-breathing children. Methods A quasi-experimental pre–post study was conducted in a school-based pediatric population . Fourteen children aged 9–12 years were recruited, including seven mouth-breathing and seven nasal-breathing controls. Salivary gtfB expression was quantified using real-time PCR and normalized to a housekeeping gene . Statistical analyses were performed using the Mann–Whitney and Wilcoxon tests. Results gtfB gene expression was significantly higher in the mouth-breathing group compared with the control group (p < 0.05), indicating increased virulence potential under altered breathing conditions. Following 14 days of Lactobacillus reuteri Prodentis administration, a downward trend in gtfB expression was observed; however, the change did not reach a statistically significant level (p = 0.398), suggesting relative stability of gtfB virulence gene expression. Conclusion Short-term probiotic exposure demonstrated limited modulation of gtfB expression, indicating relative stability of Streptococcus mutans virulence regulation under mouth-breathing–associated dysbiotic conditions.