Inhibitory effects of saliva as a suspending fluid on attachment of oral bacteria to hydroxyapatite and titanium

•Saliva affected cell surface properties of oral streptococci.•Saliva as a suspending liquid inhibited attachment of oral streptococci.•Saliva inhibited attachment by changing cell surface properties.•No effect of saliva was found on Actinomyces naeslundii. This study aims to examine the influence of saliva on the attachment of oral bacteria to hydroxyapatite and titanium surfaces in an in vitro setting using saliva as a suspending fluid for the bacterial cells, and to investigate the changes in bacterial surface physicochemical properties (hydrophobicity and charge) induced by saliva. Saliva collected from human donors was used to treat five strains of oral bacteria. The surface hydrophobicity and charge of the treated cells were measured. The effects of saliva as a suspending fluid on attachment of the strains to hydroxyapatite and titanium were investigated. Saliva was found to inhibit the attachment of four streptococcal strains by up to 100-fold. The inhibitory effects were potentially due to changes in cell-surface physicochemical properties induced by saliva. These effects were, however, not observed on Actinomyces naeslundii. The results suggest that saliva may reduce bacterial colonization by oral streptococci and that using saliva as a suspending fluid may be a useful addition for bacterial attachment studies.