Development of a method to detect secretory mucinolytic activity from Candida albicans

Ultrastructural examinations of sites where Candida albicans invaded the bowel wall after oral intragastric inoculation of infant mice suggested that blastoconidia are capable of progressive extracellular digestion of the intestinal mucus barrier. Microplate assay methods, based on biotin or digoxigenin-labelling systems, were therefore devised for quantitation of protease and glycosidase activities against the glycoprotein mucin. Labelled mucin was adsorbed on microplate wells, incubated with sample to be assayed for enzyme activity, and the remaining labelled mucin was quantitated by spectrophotometry. Proteolytic activity against mucin was demonstrated using concentrated culture filtrate of C. albicans strain LAM-1, grown in yeast nitrogen base medium containing mucin as sole nitrogen source. The activity was inhibited by boiling for 10 min or by incubation with the aspartyl proteinase inhibitor pepstatin A.