Isolation and Characterization of an Actinomyces viscosus Aggregation Factor That Mediates Coaggregation with Porphyromonas gingivalis

Intergeneric coaggregaion is responsible for the complexity of the microbiota in human dental plaque and is believed to be importart in the initial colonization by bacteria of the human oral cavity. Actinomyces viscosus (A. viscosus), an early colo-nizer of the tooth surface, may enhance subsequent colonization by Porphyromonas gingivalis (P. gingi-valis) which is associated with adult periodontitis. The purpose of this study was to isolate and charac-terize the A. viscosus. aggregation factor (AvAF) that mediates coaggregation with P. gingivalis. AvAF was isolated from A. viscosus sonic extract (SE) by gel filtration on Sephacryl S-400 HR, by hydrophobic interacion chromatography on HiTrap Octyl Sepharose 4 FF, and by ion exchange chro-matography on HiTrap Q. The specific activity increased 12-fold with a yield of 2.5%. Sodium dodecyl sulfate polya-crylamide gel electrophoresis analysis of AvAF revealed a protein band of high molecular weight in excess of 200 kDa. Carbohydrate was detected as the only other material coinciding with the protein band, indicating that the AvAF was a glycoprotein. Immunoblotting analysis indicated that AvAF bound to P. gingivalis cells. AvAF was sensitive to sodium metaperiodate treatment but not to heat or protease treatment. These data suggest that the carbohydrate component of AvAF mediated coag-gregation with P. gingivalis cells. AvAF also inhib-ited coaggregation with other periodontal disease -associated bacteria such as Prevotella intermedia, Fusobacterium nucleatum, Capnocytophaga ochracea.