Background: C. albicans and C. dubliniensis are very closely related, however clinical and laboratory data suggest that C. albicans is more virulent. The reasons for this are unclear. Adherence to human cells is an important microbial virulence factor. Previous studies that compared adhesion of C. albicans and C. dubliniensis to human epithelium have yielded conflicting results. The ALS gene family is a gene family that encodes proteins involved in adhesion in these Candida species. However, the ALS genes have been studied in C. albicans, but not C. dubliniensis to date.
Methods: Adhesion of C. albicans and C. dubliniensis to human cells was determined using the buccal epithelial cell (BEC) adhesion assay and the monolayer adhesion assay. Expression of ALS genes from both species following growth in YEPD broth was assessed using RT-PCR.
Results: The two adhesion models yielded contrasting results. C. dubliniensis genotype 1 strains adhered to BECs in greater numbers than C. dubliniensis genotypes 2-4 (P < 0.001), whereas C. dubliniensis genotype 4 cells adhered to the monolayer in greater numbers than C. dubliniensis genotype 3 (P < 0.01). C. dubliniensis ALSD1, ALSD3, ALSD4 and ALSD5 were expressed when C. dubliniensis CD36 was grown in YEPD at 37°C.
Conclusion: The two adhesion models appear to be measuring different types of candidal adhesion. All eight C. albicans ALS genes are expressed when C. albicans cells are grown in YEPD at 37°C, whereas only four of the six C. dubliniensis ALS genes are expressed under these conditions.
This study was supported by DDSH and HRB (Grant Number RP/2004/226).