Relationship between colonial morphology and adherence of Streptococcus pneumoniae

Phase variants in colonial opacity of pneumococci differ in the ability to colonize the nasopharynx of infant rats. To explain this observation at a cellular level, we compared the ability of opacity variants to adhere to buccal epithelial cells, type II pneumocytes, or vascular endothelial cells and to the glycoconjugates that represent the cognate receptors at each of these sites. The transparent phenotype was associated with enhanced adherence to buccal cells (approximately 100%) and their receptor relative to that of the opaque variants. Only modest differences in adherence (< 45%) were demonstrated to resting lung and vascular cells. In contrast, adherence of transparent variants increased by 90% to lung cells stimulated with interleukin-1 and by 130% to endothelial cells stimulated with tumor necrosis factor. In contrast, cytokine stimulation did not influence the adherence of opaque pneumococci. This difference correlated with the unique ability of transparent variants to adhere to immobilized GlcNAc and to cells bearing transfected platelet-activating factor receptors. These results suggest that the mechanism of enhanced colonization of the nasopharynx in vivo by transparent as compared with opaque phase variants involves a greater ability to adhere to both GlcNAc beta 1-3Gal on buccal epithelial cells and GlcNAc and PAF receptors on cytokine-activated, as opposed to resting, lung and endovascular cells.