Molecular and genetic analyses of Actinomyces spp.

Members of the genus Actinomyces are predominant primary colonizers of the oral cavity and play an important role in initiating plaque development. Th ese bacteria have evolved unique mechanisms that favor colonization and per sistence in this micro-environment. The expression of cell-surface fimbriae is correlated with the ability of these bacteria to adhere to specific rec eptors on the tooth and mucosal surfaces, and to interact with other plaque bacteria. The elaboration of sialidase is thought to enhance fimbriae-medi ated adherence by unmasking the fimbrial receptors on mammalian cells. The presence of certain cell-associated or extracellular enzymes, including tho se involved in sucrose or urea metabolism may provide the means for these b acteria to thrive under conditions when other growth nutrients are not avai lable. Moreover, these enzyme activities may influence the distribution of other plaque bacteria and promote selection for Actinomyces spp. in certain ecological niches. The recent development of a genetic transfer system for Actinomyces spp, has allowed for studies the results of which demonstrate the existence of multiple genes involved in fimbriae synthesis and function , and facilitated the construction of allelic replacement mutants at each g ene locus. Analyses of these mutants have revealed a direct correlation bet ween the synthesis of assembled fimbriae and the observed adherence propert ies. Further genetic analysis of the various enzyme activities detected fro m strains of Actinomyces should allow for an assessment of the role of thes e components in microbial ecology, and their contribution to the overall su ccess of Actinomyces spp. as a primary colonizer and a key player in oral h ealth and disease.