Adhesion of Candida albicans to oral streptococci is promoted by selective adsorption of salivary proteins to the streptococcal cell surface

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Abstract
Adhesion of Candida albicans to saliva-coated surfaces is an important early step in the colonization of the oral cavity. C. albicans cells also adhere to several species of oral streptococci including Streptococcus gordonii, Streptococcus oralis and Streptococcus sanguinis in what are believed to be multi-modal interactions. It is now demonstrated that incubation of streptococcal cells of these species with human parotid saliva further promotes the adhesion of C. albicans cells by up to 2·3-fold. Various species of streptococci were shown to adsorb different protein components of parotid saliva to their cell surfaces. The basic proline-rich proteins (bPRPs), to which C. albicans cells bind on nitrocellulose blot overlay, were strongly adsorbed to the surface of S. gordonii cells but not to S. oralis cells. Parotid saliva that was pre-adsorbed with S. gordonii cells and then applied to hydroxylapatite beads was <50% effective at supporting adhesion of C. albicans compared with control (non-adsorbed) saliva, demonstrating that bPRPs are major pellicle receptors. C. albicans cells did not adsorb bPRPs from fluid-phase parotid saliva. Following size-exclusion chromatography of parotid saliva samples, pooled fractions enriched in bPRPs promoted maximal adhesion of C. albicans to S. gordonii cells. The results demonstrate that C. albicans cells recognize only surface-bound forms of bPRPs and suggest that these proteins adsorbed to enamel or to streptococcal surfaces promote C. albicans adhesion and oral colonization.