Lactose-reversible coaggregation between oral actinomycetes and Streptococcus sanguis.

Freshly isolated strains of oral actinomycetes were obtained from human dental plaque and were tested for the ability to coaggregate with common laboratory stock strains of Streptococcus sanguis. Strains belonging to the genera Actinomyces, Arachnia, Bifidobacterium, and Bacterionema were isolated. Only members of the genus Actinomyces coaggregated with the streptococci, and only Actinomyces viscosus and Actinomyces naeslundii exhibited lactose-reversible interactions. A total of 61 strains, consisting of all of the A. viscosus isolates and 86% of the A. naeslundii isolates, coaggregated; 87% inhibited lactose-reversible coaggregation. On the basis of this property and the altered ability of strains to coaggregate after heat treatment of the cells, we delineated four coaggregation groups. The other 13% of the strains constituted a fifth group, which was characterized by a pattern of closely related interactions that were not reversed by lactose. Compared with previously characterized coaggregation properties determined with stock culture strains of actinomycetes, more than 80% of these fresh isolates exhibited identical coaggregation properties. Thus, most of the coaggregation between freshly isolated oral actinomycetes and streptococci involves lactose-reversible cell-cell interactions, which suggests that such coaggregation is mediated by a network of lectin-carbohydrate interactions between complementary cell surface structures on the two cell types.