Ecology of human oral lactobacilli

Lactobacilli were found in saliva, on teeth, and on the dorsum of the tongue, the vestibular mucosa, and the hard palate in humans. Their proportions in saliva, expressed as percentage of the anaerobically cultivable flora, were 10- to 100-fold higher than those on the tooth surface, but were comparable to those on the epithelial surfaces. The adherence of Lactobacillus casei and L. fermenti to oral surfaces was compared with that of streptomycin-labeled Streptococcus sanguis and S. salivarius by using in vitro-cultivated cells. The affinity of both Lactobacillus species for the tooth surface was very low compared with that of S. sanguis but was somewhat higher than that of S. salivarius. The lactobacilli and both Streptococcus species adhered to a similar extent to the dorsum of the tongue, whereas the affinity of the lactobacilli and S. salivarius for the vestibular mucosa was about one-half of that of S. sanguis. The results suggest that the affinity of lactobacilli for oral surfaces significantly influences their proportional distribution in the mouth. The relatively low affinity of lactobacilli for the tooth surface suggests that their recognized association with carious lesions and mechanical appliances under certain conditions may be due primarily to mechanical retention rather than unique growth conditions.