Investigation of the Antagonistic Effect of Enterococcus Durans Strains on Microorganisms Responsible for Black Tooth Staining

Objective: Black stain is an extrinsic tooth discoloration, characterized by dark lines or incomplete pigmentation along the gingival margin in the cervical third of the tooth. Bacteria from the genus Capnocytophaga, particularly facultative anaerobic, gram-negative, fusiform-shaped species, are believed to contribute to its formation. Lactic acid bacteria, such as Enterococcus durans, are gram-positive bacilli that have been extensively studied for their probiotic properties. The aim of this study was to evaluate the antagonistic effects of three E.durans strains against bacteria isolated from black tooth stain and Capnocytophaga ochracea. Materials and Methods: Samples were collected from 50 children aged 9-12 years at the Pediatric Dentistry Department of XXX University. The samples were diluted and cultured on trypticase bacitracin blood polymyxin agar to isolate cultivable bacteria associated. Isolates were identified using biochemical tests, including indole, catalase, oxidase, and Gram staining under 8% CO₂ conditions. The antagonistic effects of the E.durans strains against both black stain bacteria and C.ochracea ATCC 27872 were assessed on blood agar plates. Data analysis was conducted using SPSS 25.0. The normality of data distribution was assessed using the Kolmogorov-Smirnov test. Absolute and logarithmic bacterial counts were statistically evaluated using the Kruskal-Wallis test. Results: Among the tested strains, E.durans K2-2 exhibited the strongest antagonistic effect against C.ochracea, with a 12mm inhibition zone. Conclusion: These results suggest that E.durans strains with probiotic potential may contribute to the prevention of dental caries by inhibiting associated bacterial species. Further studies are needed to investigate their mechanisms of action and to evaluate their potential use in preventive oral healthcare.