Candida albicans virulence factor expression in tissue and broth culture

Objectives: The study compared the expression of candidal virulence factors in an in vitro reconstituted human oral epithelial (RHE; Skinethic Laboratories, Nice France) model and in the tissue maintenance medium devoid of tissue. Methods: Candida albicans (n=19) originated from a range of oral conditions including oral candidoses, oral cancer and healthy oral mucosa. The strains were cultured in defined media for 24 h at 37°C and harvested by centrifugation. Yeast were washed (×3) in phosphate buffered saline (PBS) and adjusted to 4×10⁷ cells/ml in the maintenance medium for RHE. One-ml of the preparation was used to infect a 0.5 cm² area of RHE and a further 1-ml portion was cultured in the absence of the tissue. Incubation was at 37°C in a CO₂ enriched environment for 24 h. Reverse transcription PCR (RT-PCR) was then used to determine expression of 9 secreted aspartyl proteinase (SAP) genes, 4 phospholipase genes and 8 Agglutinin-Like Sequence (ALS) genes. Furthermore, the morphological appearance of the Candida in the presence and absence of the RHE was also established. Results: Comparison of the two culture environments showed that ALS gene expression appeared to be independent of the presence of the oral epithelium. In both broth and tissue environments, consistent expression of ALS 1, 3 and 5 was found. Similarly, expression of SAPs 1-3, 7 and 8 was evident, with variable phospholipase gene expression also detected for the two environments. The morphology of Candida albicans was consistent between the two growth environments. Conclusions: The in vitro expression of Candida virulence factors under the described culture environments appears to primarily relate to the culture medium as opposed to the presence of the oral epithelium. Strain differences in expression of these factors was however evident.