Abstract Authors
Colleen K Mc Quire - Department of Microbiology and Biochemistry, University of the Free State
Maphori Maliehe - Department of Microbiology and Biochemistry, University of the Free State
Nozethu Mjokane - Department of Microbiology and Biochemistry, University of the Free State
Olihile M Sebolai - Department of Microbiology and Biochemistry, University of the Free State
Abstract Description
Cryptococcus neoformans is a basidiomycetous yeast that rose from being an obscure fungus to an important fungal pathogen. Part of its success is attributed to its arsenal of virulence factors that allow it to subvert the immunological response in a susceptible host. This includes the production of proteases that could permeabilise the phagosomal membrane, leading to internalised cells escaping. This project sought to assess if a protease inhibitor, decanoyl-RVKR-chloromethyl ketone (DEC-RVKR-CMK), could decrease cryptococcal growth and increase their susceptibility towards macrophage phagocytosis. The in vitro susceptibility of cryptococcal cells was assessed by measuring the optical density of the cells following exposure to different DEC-RVKR-CMK concentrations. Additionally, the DEC-RVKR-CMK-treated cells and non-treated cells were co-cultured with macrophages to assess their susceptibility to macrophage phagocytosis by using the pHrodo stain to assess the internalisation of cryptococcal cells by macrophages and a spread plate method to enumerate cells that survived internalisation. It was shown that a 10-fold increase in DEC-RVKR-CMK concentration led to the growth of cryptococcal cells being inhibited in a dose-dependent manner. In the study, 0.1 mM was defined as the minimum inhibition concentration, and it led to over 75 % growth inhibition. There was no difference (p > 0.05) in the efficiency of macrophages to internalise DEC-RVKR-CMK-treated cells and non-treated cells. However, no colonies of DEC-RVKR-CMK-treated cells could be recovered on mycological agar, while non-treated cells yielded colonies on the agar. The in vitro preliminary data obtained in this study suggest DEC-RVKR-CMK may be ideal for controlling cryptococcal growth. The clinical relevance of the study may lie in impairing the ability of cryptococcal cells to escape from macrophages, thus avoiding immunoprocessing. It is thus prudent to show if this quality can be observed in other C. neoformans strains and elucidate the molecular mechanism underpinning the reported observations.
