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Virulent M protein-containing strains of Streptococcus pyogenes were found to adhere well to human pharyngeal cells in vitro. In contrast, an avirulent M - strain and an enteropathogenic Escherichia coli strain adhered feebly. When various rat tissues were exposed to mixtures of a virulent S. pyogenes strain and an enteropathogenic E. coli strain, the relative proportions of the two pathogenic strains recovered from mucosal surfaces differed among the sites studied. S. pyogenes cells were found to adhere in higher proportions than enteropathogenic E. coli cells to the mucosal surfaces of rat tongues, whereas on surfaces of the urinary bladder, their affinities were reversed. The data indicate that bacterial adherence is influenced by the specificity of both the bacterial and epithelial surfaces, and they suggest that adherence may influence the tissue tropisms of pathogens. Early stationary-phase cells of S. pyogenes attached better to epithelial cells than did bacteria in other growth phases. The adherence of S. pyogenes cells was impaired by pretreatment with trypsin, wheat germ lipase, Tween 80, Triton X-100, sodium lauryl sulfate, heat at 56 C, anti-group A antiserum, the presence of phospholipids, and preincubation of the epithelial cells with Streptococcus salivarius cell walls. Altering the pH or treatment with ethylenediaminetetraacetic acid had no effect on the ability of S. pyogenes cells to adhere.

The mouth harbors organisms in great abundance; yet their variety is limited and it is noteworthy that some species present in the mouth are not found elsewhere. There are many antibacterial substances in the mouth, some of which may contribute to the control of the microbial flora in the mouth. The activity of some is enhanced in the presence of specific antibody, e.g. lactoferrin, although others appear unaffected, e.g. lactoperoxidase. Opinions differ as to whether the level of immunoglobulins in human saliva can be related to caries. Although it has been established in principle that caries can be prevented in animals by means of vaccination, substantial work remains to be done before a vaccine will be available for testing in humans.

The release of (51)Cr from labelled colon cells was used to assess a possible lymphocytotoxic effect of peripheral blood lymphocytes from patients suffering from recurrent aphthous ulceration. No significant (p > 0.03) difference was observed between the isotope release following incubation with patients' or control lymphocytes. The absence of such a lymphocytotoxic effect, detectable with oral epithelial cells, is discussed in relation to the role of cellular hypersensitivity in the pathogenesis of ulcerative colitis and aphthous ulceration.