The influence of subinhibitory concentrations of conventional and experimental antifungal drugs on the expression of the iC3b binding protein in Candida albicans strains during filamentation

The influence of six antifungal agents on the expression of the fungal iC3b binding protein was studied in germ-tubes and the mycelial form of several Candida albicans strains. All antifungal agents inhibited not only the yea st-mycelial transformation. but also the formation of rosettes consisting o f complement-coated sheep erythrocytes (EAiC3b) bound to the mycelial form of C. albicans. Immunofluorescence as well as ELISA, employing the monoclon al antibody OKM-1 which recognizes the cc chain of human CR3 and which cros s-reacts with the fungal iC3b binding protein: revealed that subinhibitory concentrations of 0.1 mg l(-1) (which did not affect the growth of either g erm-tubes or the mycelial form of C. albicans) inhibited the expression of the iC3b binding protein, while lower concentrations (0.01 mg l(-1)) allowe d a comparable and sometimes even slightly higher expression of this protei n, in comparison with the untreated control. However, treatment with antifu ngal agents apparently did not lead to a major cleavage of the protein. The dependence of the amount of the iC3b binding protein expressed on the conc entration of added antifungal drugs and on the morphological forms of indiv idual C. albicans isolates suggests a drug dependent influence on the expre ssion of this protein and a possible association with the changing virulenc e of C. albicans strains during antifungal therapy. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.