The human oral cavity is a highly diverse ecosystem with more than 500 species of bacteria, including cultivable and non-cultivable species. It is believed that infection due to a group of Gram-negative anaerobes - known as the 'red-complex' - is responsible for causing periodontitis, a chronic inflammation of the tooth supporting tissue that leads to tooth loss. My lab studies the pathogenic mechanisms of bacteria that constitute the red-complex; namely, Porhyromonas gingivalis, Tannerella forsythia (formerly Bacteroides forsythus) and Treponema denticola (a spirochete). Our overall objectives are to gain a better understanding of how these pathogenic bacteria initiate colonization, form biofilms and initiate tissue destructive host immune responses critical for disease progression. The research focuses on identifying the pathogen-associated molecular pattern molecules (PAMPs) and virulence factors as well as host immune responses to these microbial products.  Understanding of molecular interactions between oral pathogens or their products with host would lead to the future development of therapeutic strategies, such as vaccines, for periodontitis. Towards this goal, we developed genetic systems in non-pathogenic oral streptococci (Streptococci gordonii) for expression and delivery of vaccine antigens.