albicansto form mucosal biofilms in this device and characterized the kinetics of mucosal biofilm formation

albicansto form mucosal biofilms in this device and characterized the kinetics of mucosal biofilm formation. form biofilms in the presence ofC. albicanscould not be explained by a growth-stimulatory effect since the streptococci were unaffected in their growth in planktonic coculture withC. albicans. Conversely, the presence of streptococci increased the ability ofC. albicansto invade organotypic models of the oral and esophageal mucosae under conditions of salivary flow. Moreover, characterization of mucosal invasion by the biofilm microorganisms suggested that this esophageal mucosa is usually more permissive to invasion than the oral mucosa. In summary,C. albicansand commensal oral streptococci display a synergistic conversation with implications for the pathogenic potential ofC. albicansin the upper gastrointestinal tract. == INTRODUCTION == Candida albicansis a pleomorphic fungus that colonizes the gastrointestinal (GI) and genitourinary mucosal surfaces of humans, persisting in these niches as a commensal in up to 60% of healthy individuals (5,50). Alterations in host immunity, bacterial flora or local environmental factors, such as oral salivary flow, are believed to determineC. albicanstransition from a commensal to an opportunistic pathogen, capable of causing a wide Mirodenafil range of superficial mucosal or life-threatening systemic infections (10,36,44). At mucosal environments,C. albicanscoexists with a highly diverse bacterial flora. For instance, in the human oral cavity, more than 700 different bacterial species have been described to exist, with a single individual harboring several hundreds of bacterial phylotypes (15). Resident oral microorganisms colonize hard surfaces such as teeth and prosthetic devices forming complex polymicrobial biofilm structures (42,65). In health, mucosal biofilm growth in the oral cavity is limited by a rapid epithelial turnover and host innate immune defenses at the mucosal interface (18). However, immunosuppression allows the formation of mucosal biofilms, leading to the clinical appearance of thrush (14). Our group has shown that these biofilms are not only comprised by a dense network ofCandidacells but also by commensal oral bacteria in close association withCandida(20). Thus, the conversation ofC. albicanswith commensal resident bacteria is bound to be an important determinant ofC. albicanscolonization and persistence at mucosal niches and is likely to modulate its virulence at these sites. Oral streptococci from the viridans group are the most ubiquitous and abundant primary colonizers of oral surfaces (1,16,38). These streptococci are considered commensal organisms of limited virulence and are generally associated with oral health. However, viridans streptococci can cause life-threatening systemic infections if the oral mucosa is usually disrupted and the host defense mechanisms are compromised (28,34).C. albicanshas the ability to coaggregate with a variety of oral bacteria, including most species from the viridans group of streptococci (26,30,33). Physically associated cells ofC. albicansand streptococci have been demonstratedin RAC1 vivo, in tooth-associated biofilms, via fluorescencein situhybridization (FISH), with streptococcal cells forming corn-cob-like structures aroundC. albicanshyphae (65). The mechanisms mediating coaggregation betweenC. albicansand oral streptococci, specificallyStreptococcus gordonii, have been characterized as adhesin-receptor interactions. The Mirodenafil adhesins around the streptococcal surface have been identified as the cell surface-associated, antigen I/II family adhesins, SspA and Mirodenafil SspB (4,31), while the hyphal wall protein Als3p has been shown to serve as receptor for the streptococcal adhesin SspB (52). Furthermore,C. albicanshas been demonstrated to form mixed-species biofilms withS. gordoniion plastic wells under static conditions, and contact withS. gordoniihas been shown to enhanceC. albicansfilamentation (4). Based on the knownin vitroandin vivointeractions betweenC. albicansand oral streptococci, it is likely that the two organisms form an interkingdom partnership that promotes mucosal colonization or contamination. Since hyphal formation is promoted by streptococci, while it is also a prerequisite for tissue invasion (35,51), it is possible that contact ofC. albicansand streptococci may alter the invasive phenotype of the former. The goal of our work was Mirodenafil to characterize the role of the conversation betweenC. albicansand streptococci in the pathogenesis of mucosal contamination using biologically relevantin vitromodel systems. The conversation ofC. albicansand streptococci as abiotic surface biofilms was studied in standard flow cell devices under salivary flow. However, since no system existed that allowed the study of mucosal biofilms under flow conditions, we designed a novel flow cell device able to harbor an organotypic mucosal tissue analogue, where microorganisms can form biofilms using saliva-supplemented medium as nutrient source, simulating environmental conditions in the upper GI tract. Since the type of mucosal epithelium that lines the alimentary tract mucosa may serve as an ecological determinant of invasive contamination, we testedCandida-streptococci interactions in two organotypic mucosal.