Investigating O-linked manan-mediated adhesion of Candida albicans to endothelium

Objectives: Using C.albicans strains deficient in genes encoding mannosyl-transferases (Mnt), which regulate  length of O-linked mannans, this study aimed to determine the role of O-linked manans in mediating binding to the endothelium under conditions of flow in vitro and in an embryonic Danio rerio(zebrafish) infection model.

Methods: Suspensions of wild-type or Mnt mutated C.albicans strains (Mnt1 and Mnt2) were flowed across confluent monolayers of a human microvascular endothelial cell line (HMEC-1) and numbers binding measured. Zebrafish embryos were inoculated with C.albicans (GFP-labelled, Mnt mutant and wild-type strains) and mortality determined at 18h. In addition, CFU counts were taken to assess injection efficiencies, dose-response and colonization. C.albicans was also visualized in vivousing fluorescent microscopy.

Results: C.albicans replicated within embryonic zebrafish, turned hyphal and caused a dose-dependent increase in mortality with a maximal mortality rate of ~70% at 18h for the wild-type strain. Once bound to the endothelium in vivo C.albicans turned hyphal and caused extensive tissue damage. C.albicans deficient in the genes encoding O-linked mannans adhered significantly (p<0.05) less well to HMEC-1 monolayers in vitrounder flow conditions and were significantly (p<0.05) less virulent in the zebrafish infection model than wild-type controls.

Conclusions: Fluorescent microscopy allows visualization of C.albicans adherence and damage in vivo. O-linked mannans contribute to adhesion of C.albicans to the endothelium in vitro, and mortality rates in the zebrafish embryonic infection model.