Characterization of the adherence properties of Streptococcus salivarius

The adherence and aggregation properties of 46 human oral Streptococcus salivarius isolates were examined. A total of 41% of the isolates aggregated with whole human saliva, 50% aggregated with human erythrocytes, and 85% adhered to human buccal epithelial cells. Strains that aggregated with saliva and erythrocytes usually reacted with Streptococcus group K typing serum whereas the non-hemagglutinating strains did not. K+ strains also adhered more strongly to human buccal epithelial cells than K- strains. All isolates coaggregated with Fusobacterium nucleatum LF and Bacteroides asaccharolyticus 2D, 91% coaggregated with Veillonella alcalescens V1, and 50% coaggregated with Veillonella parvula V4. S. salivarius HB aggregated with saliva from 15 different human donors and aggregated with human erythrocytes irrespective of the blood group. This strain only weakly aggregated with rat saliva or rat erythrocytes. We isolated mutants which concomitantly lost the ability to agglutinate erythrocytes, aggregate with saliva, and bind to buccal epithelial cells, but retained their interbacterial aggregation properties. A second class of mutants lost the ability to coaggregate with Veillonella, but these mutants retained all of the other aggregation properties. Treatment of S. salivarius HB cells with pronase or subtilisin destroyed their ability to aggregate with saliva and erythrocytes and to bind to buccal epithelial cells. The unique characteristics of the aggregation and adherence reactions were suggested by differences in the rate of loss of activity during protease treatment and in the response to chemical modification. The presence of saliva did not affect hemagglutination and adherence to buccal epithelial cells. Binding of the salivary aggregating factor to the bacteria could be distinguished from aggregation on the basis that the latter required divalent cations. The factor involved in coaggregation with F. nucleatum LF was physicochemically different from the other factors, since it was resistant to heat and to extraction with trichloroacetic acid, aqueous phenol, sodium dodecyl sulfate, and formamide, but was sensitive to proteases and was present in both classes of mutants. Coaggregation with V. alcalescens was not sensitive to proteases. A variety of mono- and disaccharides had no influence on any of the reactions tested.