Role of AI-2 in oral biofilm formation using microfluidic devices
Biofilms are highly organized bacterial structures that are attached to a surface. They are ubiquitous in nature and may be detrimental, causing numerous types of illnesses in living organisms. Biofilms in the human oral cavity are the main cause of dental caries and periodontal diseases and can act as a source for pathogenic organisms to spread within the body and cause various types of systemic diseases. Streptococcus mutans is the primary etiological agent of dental caries, the single most chronic childhood disease. In many cases, quorum sensing (QS) is required for initial formation and subsequent development of biofilms and the signaling molecule autoinducer 2 (AI- 2) has been well studied as an inter-species QS signaling molecule. However, recent reports also suggest that AI-2-mediated signaling is important for intra-species biofilm formation in both Gram-negative and positive bacteria. Therefore, there is significant interest in understanding the role of different QS signals such as AI-2 in oral biofilm formation. Microfluidic devices provide biomimetic environments and offer a simple method for executing multiple stimuli experiments simultaneously, thus, can be an extremely powerful tool in the study of QS in biofilms. In this study, we report conditions that support the development of S. mutans biofilms in microchannel microfluidic devices, and the effects of extracellular addition of chemically synthesized (S)-4,5-dihydroxy-2,3-pentanedione (DPD; precursor of AI-2) on mono-species S. mutans luxS (AI-2 deficient strain) biofilm formation using a gradient generating microfluidic device. S. mutans wild type (WT) and luxS biofilms were developed in nutrient rich medium (25% brain heart infusion medium, BHI + 1% sucrose) for up to 48 h. Maximum biofilm formation with both strains was observed after 24 h, with distinct structure and organization. No changes in S. mutans luxS biofilm growth or structure were observed upon exposure to different concentrations of AI-2 in a gradient generating device (0 to 5 M). These results were also validated by using a standard 96-well plate assay and by verifying the uptake of AI-2 by S. mutans luxS. Our data suggest that extracellular addition of AI-2 does not complement the luxS deletion in S. mutans with respect to biofilm formation.
Kim, Sun Ho (2008). Role of AI-2 in oral biofilm formation using microfluidic devices. Master's thesis, Texas A&M University. Available electronically from