Although its clinical appearance suggest dental plaque is an amorphous bacterial accumulation, recent studies suggest not only structural organization of specific bacteria but an ordered process of maturation. The early accumulation of streptococci, particularly Streptococcus sanguis is followed by the appearance of Gram-positive and Gram-negative filaments. One of the major factors related to the appearance of these filaments is the interaction between specific surface components of the streptococci with analogous components of the filaments. One form of aggregate which results from this interaction has been termed """"""""corncobs"""""""" because of their resemblance to an ear of corn. These units which are often observed in the superficial layers of plaque were originally thought to be unique to aggregates formed by S. sanguis and Bacterionema matruchotii, a Gram-positive aerobic rod. We have recently found that corncobs are also formed between S. sanguis and Fusobacterium nucleatum, a Gram-negative, anaerobic rod. These anaerobic rods are among the most numerous organisms found in subgingival plaque and plaque associated with certain types of periodontal disease. Thus, these aggregates could serve as a connecting link between supra and subgingival plaque. The object of the proposed studies is to characterize the interactions between S. sanguis, B. matruchotii and F. nucleatum and determine the molecular basis of corncob formation. This will be accomplished using the following methods: i. dissecting the cell surface and assaying the fractions for receptor activity, ii. comparing the composition of the surfaces of strains which do not form corncobs with those that do, iii. comparison of the surface of corncob negative mutants with the positive parent strains, iv. the effects of environment on corncob formation and resulting surface changes will also be assayed. In addition to biological activity the extracts will be characterized chemically and immunochemically using combinations of analytical electrophoretic methods, isotopic labeling techniques, column chromatography and analytical chemistry. The results of these studies could provide an understanding of the surface polymers of oral bacteria which are associated with corncob formation and suggest strategies which could be employed to inhibit plaque maturation.
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