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

Activity of anti-CR3-RP polyclonal antibody against biofilms formed by Candida auris, a multidrug-resistant emerging fungal pathogen

Fungal biofilm has remained a serious medical problem that complicates treatment of mycoses. In particular, once biofilms are formed, they display high levels of resistance against most common antifungals. Candida auris is currently considered as a serious emerging fungal pathogen frequently exhibiting high levels of resistance to antifungals. Recent studies have confirmed that C. auris shares similarity with Candida albicans in regards to virulence-associated proteins involved in adherence and biofilm development. Complement receptor 3-related protein (CR3-RP) is one of the key surface antigens expressed by Candida species during biofilm formation. Here, we have investigated the presence of this cell surface moiety on the surface of C. auris, as well as the potential of anti-CR3-RP polyclonal antibody (Ab) to inhibit biofilm formation by this emerging fungal pathogen. Using indirect immunofluorescence and ELISA, we were able to confirm the presence of CR3-RP in C. auris cells within biofilms. Further, not only anti-CR3-RP Ab was able to inhibit biofilm formation by multiple C. auris strains when added during the adherence phase, but it also demonstrated activity against C. auris 24-h pre-formed biofilms, which compared favorably to levels of inhibition achieved by treatment with current conventional antifungals fluconazole, amphotericin B, and caspofungin. Overall, our data demonstrate the presence of this antigen on the surface of C. auris and points to the potential of anti-CR3-RP Ab in eradication of biofilms formed by this novel fungal pathogen.

Antibody response to the 45 kDa Candida albicans antigen in an animal model and potential role of the antigen in adherence

The Candida antigen CR3-RP (complement receptor 3-related protein) is supposed to be a 'mimicry' protein because of its ability to bind antibody directed against the alpha subunit of the mammalian CR3 (CD11b/CD18). This study aimed to (i) investigate the specific humoral isotypic response to immunization with CR3-RP in vivo in a rabbit animal model, and (ii) determine the role of CR3-RP in the adherence of Candida albicans in vitro using the model systems of buccal epithelial cells (BECs) and biofilm formation. The synthetic C. albicans peptide DINGGGATLPQ corresponding to 11 amino-acids of the CR3-RP sequence DINGGGATLPQALXQITGVIT, determined by N-terminal sequencing, was used for immunization of rabbits to obtain polyclonal anti-CR3-PR serum and for subsequent characterization of the humoral isotypic response of rabbits. A significant increase of IgG, IgA and IgM anti-CR3-RP specific antibodies was observed after the third (P<0.01) and the fourth (P<0.001) immunization doses. The elevation of IgA levels suggested peptide immunomodulation of the IgA1 subclass, presumably in coincidence with Candida epithelial adherence. Blocking CR3-RP with polyclonal anti-CR3-RP serum reduced the ability of Candida to adhere to BECs, in comparison with the control, by up to 35 % (P<0.001), and reduced biofilm formation by 28 % (P<0.001), including changes in biofilm thickness and integrity detected by confocal laser scanning microscopy. These properties of CR3-RP suggest that it has potential for future vaccine development.

Influence of sub-inhibitory concentrations of conventional antifungals on metabolism of Candida albicans and on its adherence to polystyrene and extracellular matrix proteins

Five antifungal agents with different mechanisms of action were compared for their ability to affect mitochondrial dehydrogenase activity and adherence capacity of Candida albicans to polystyrene and extracellular matrix proteins. Only amphotericin B inhibited mitochondrial dehydrogenase activity when the culture medium was supplemented with galactose. 5-Fluorocytosine and terbinafine did not affect this activity, whereas itraconazole and fluconazole improved it. Furthermore, in these experimental conditions, the effect of sub-inhibitory concentrations of antifungals on adherence was dependent on the tested antifungal and the adherence surface: amphotericin B inhibited adherence to polystyrene and fibrinogen, but improved adherence to extracellular matrix. For all surfaces tested, when culture medium was supplemented with galactose, fluorocytosine did not affect adherence, and itraconazole, fluconazole and terbinafine inhibited adherence. Our results also confirmed the influence of the carbohydrates: sub-minimum inhibitory concentrations (MIC) of itraconazole increased or did not modify the mitochondrial metabolism of yeasts when the culture medium was supplemented with galactose, but this antifungal always decreased mitochondrial metabolism when the culture medium was supplemented with glucose. These data indicate that antifungals used below their MIC values can have various effects. It is important to distinguish the effects of antifungals on the metabolism of C. albicans from effects on its adherence capacity. The former effects are linked to the viability of the yeast and the latter depends on the colonization of cellular as opposed to inert surfaces.