Oral Epithelial Cell Responses to Streptococcus spp.

Substantial evidence has supported variations in the physiology, gene expression, and growth characteristics of bacteria in biofilms compared with the same species under planktonic conditions. While it has been suggested that the host may respond differently to biofilm bacteria, scant evidence is available to document the parameters of these differences. Objectives: To evaluate epithelial cell responses to bacterial challenge with planktonic versus biofilm S. gordonii, S. oralis and S. sanguinis by determining changes in levels of cytokine/chemokine in culture supernatants. The streptococcal species were used to characterize the role of prototype “early colonizers” on gene induction. Methods: Biofilms were used to better represent the form of bacteria in the subgingival sulcus within the oral cavity and to contrast with previous studies using planktonic bacteria. The biofilms were grown for three days on rigid gas permeable contact lenses (RPGL). Oral epithelial cells (OKF4) were challenged with the streptococci either grown as biofilms or using varying concentrations of planktonic bacteria similar to the number of bacteria in the biofilms. OKF4 cells were cultured in 48-well plates at 10⁵ cells/well and were challenged with the biofilms, planktonic bacteria, and RPGL controls for 3 hours under anaerobic conditions. Protein expression levels for IL-6, IL-8 and MCP-1 were determined by ELISA. Results: IL-6, IL-8 and MCP-1 levels in culture supernatants were not significantly altered following biofilm or planktonic challenge with any of the streptococcal species, compared to control levels. Conclusion: These early bacterial colonizers of the subgingival sulcus elicited a rather minimal expression of these host innate immune molecules. This is consistent with the perceived minimal virulence of these species and importance of a regulated host response to members of the commensal microbiota in the oral cavity. Supported by NIH/NIDCR DE018177 and AADR Student Research Fellowship (AR).