Candida parapsilosis Infection of Reconstituted Human Oral Epithelium

Objectives: Candida species frequently colonise oral surfaces existing as harmless commensals. However, infections often occur in debilitated patients, with Candida albicans being the most frequently cause. It is becoming increasingly evident that other non-C. albicans Candida (NCAC) species including C. parapsilosis are also important opportunistic pathogens. Despite this recognition, the virulence mechanisms of NCAC species are poorly understood. The objectives of this study were, therefore, to assess the invasive capability of C. parapsilosis in a Reconstituted Human Oral Epithelium (RHOE) and to detect C. parapsilosis secreted aspartyl proteinase (SAPP) gene expression during infection. Methods: C. parapsilosis (n=7) was used to infect RHOE for 12 and 24 h. Sections (20 µm) of this tissue were stained with concanavalin A–Alex 594 and Hoechst nucleic acid dye to assess C. parapsilosis colonisation and invasion by Confocal Scanning Laser Microscopy (CLSM). A portion of unfixed RHOE was used for RNA extraction. This RNA, together with broth culture extracts was subjected to RT-PCR targeting three SAPP genes (SAPP 1-3). Results: CLSM revealed that all strains colonised the RHOE, although the extent was strain dependent as was the morphology of infecting strains. After 12 h incubation, C. parapsilosis invaded the upper layers of the epithelium; extensive epithelial damage was only evident after 24 h. Expression of SAPP genes was again strain dependent with differences between infecting and planktonic Candida also evident. Reduced expression of SAPP3, and increased expression of SAPP1 and SAPP2 for infecting strains was detected. Conclusion: The effectiveness of RHOE as a model to study Candida virulence was confirmed and demonstrated that C. parapsilosis, whilst not highly invasive, was able to damage tissue. SAPP1 and SAPP2 could be contributing factors to the invasion process and promoting RHOE damage.