ORAL COLONIZATION BY CANDIDA ALBICANS R.D. Cannonl* W.L. Chaffin2 'Department of Oral Sciences and Orthodontics, Faculty of Dentistry, University of Otago, PO Box 647, Dunedin, New Zealand; 2Department of Microbiology and Immunology, Texas Tech University Health Sciences Center, Lubbock, Texas, USA; *corresponding author ABSTRACT: Candida albicans is a commensal yeast normally present in small numbers in the oral flora of a large proportion of humans. Colonization of the oral cavity by C. albicans involves the acquisition and maintenance of a stable yeast population. Micro-organisms are continually being removed from the oral cavity by host clearance mechanisms, and so, in order to survive and inhabit this eco-system, C. albicans cells have to adhere and replicate. The oral cavity presents many niches for C. albicans colonization, and the yeast is able to adhere to a plethora of ligands. These include epithelial and bacterial cell-surface mole- cules, extracellular matrix proteins, and dental acrylic. In addition, saliva molecules, including basic proline-rich proteins, adsorbed to many oral surfaces promote C. albicans adherence. Several adhesins present in the C. albicans cell wall have now been partially characterized. Adherence involves lectin, protein-protein, and hydrophobic interactions. As C. albicans cells evade host defenses and colonize new environments by penetrating tissues, they are exposed to new adherence receptors and respond by expressing alternative adhesins. The relatively small number of commensal Candida cells in the oral flora raises the possibility that strategies can be devised to prevent oral colonization and infection. However, the variety of oral niches and the complex adherence mechanisms of the yeast mean that such a goal will remain elusive until more is known about the contri- bution of each mechanism to colonization. Key words. Candida albicans, colonization, adherence, candidiasis. (1) Introduction The presence of Candida albicans in the oral cavity is not indicative of disease. In many individuals, C. albicans is a minor component of their oral flora, and they have no clinical symptoms. In certain sections of the population, however, oral candidiasis occurs frequently and necessi- tates antifungal therapy. Oral presentations of candidia- sis vary from the large white plaques of pseudomembra- neous candidiasis on the tongue and buccal mucosa to the palatal erythematous lesions of chronic atrophic can- didiasis, and to angular cheilitis on the labial commis- sures (Samaranayake, 1990; Scully et al., 1994; Shay et al., 1997). The primary etiological agent of oral candidiasis is the yeast C. albicans; however, other species that cause disease less commonly include C. tropicalis, C. glabrata, C. krusei, C parapsilosis, C. guilliermondii, and C. dubliniensis (Odds, 1988; Fridkin and Jarvis, 1996; Sullivan and Coleman, 1998). Sequelae of mucosal colonization, par- ticularly of the gastrointestinal tract, may include pene- tration of the vascular system by Candida cells and hematogenous dissemination (Cole et al., 1996). These cells can then infect a variety of organs in immunocom- promised individuals and cause disseminated or sys- temic disease. It is difficult to give a precise oral carriage rate for C. albicans, since this depends on the age and health of the population studied. A compilation of data from a num- ber of reports showed that the mean carriage rate for healthy individuals (no known underlying disease) was 17.7% (range, 1.9-62.3%), whereas mean carriage in hos- pitalized individuals (without clinical candidiasis) was 40.6% (range, 6.0-69.6%) (Odds, 1988). These data indi- cate that the health of an individual is a predisposing factor for C. albicans colonization. A large number of sites in the oral cavity can be colonized; in healthy individuals, C. albicans is most commonly isolated from the mid-line of the middle and posterior thirds of the tongue, the cheek, or the palatal mucosa (Arendorf and Walker, 1979, 1980; Borromeo et al., 1992). It is of interest that only a proportion of the popula- tion is colonized by C. albicans, and only a subset of these individuals develops candidiasis. Few longitudinal stud- ies have been carried out on healthy individuals to see if Candida colonization is continuous. However, daily sam- pling has shown that C. albicans carriage persisted in a proportion of healthy people and that colonization recurred in a majority of the remaining subjects (Gergely and Uri, 1966; Williamson, 1972). In a study of 163 neonates in an intensive care and surgical unit, 21 of the neonates initially carried C. albicans in their mouths, but only five yielded 6 or more yeast-positive cultures over the 17-week study period (Sharp et al., 1992). These neonates were colonized for periods of between 7 and 63 1013) 359 383 (1999)Crit Rev Oral 359 10(3)-359-383 (1999) 359 Crit Rev Oral Biol Med
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Related Documents
