Candida glabrata resistance to histatins and other antifungal proteins
Date
2007
DOI
Authors
Venuleo, Caterina
Version
OA Version
Citation
Abstract
Naturally occurring salivary antifungal proteins have been of major interest due to their potential to provide the basis for peptide antimycotics effective to combat fungal infections in the oral cavity or elsewhere. We evaluated the fungistatic activity of a number of cationic antifungal proteins with major emphasis on histatin 5, a basic protein secreted by the human parotid and submandibular glands. Histatin 5 inhibited the growth of Candida ablicans and that of other medically important Candida species such as C. kefyr, C. krusei, and C. parapsilosis with IC [50] values ranging between 10 and 20 mega/ml. Two Cryptococus neoformans strains were also sensitive (IC [50] 5.2 and 5.6 mega/ml). On the other hand, three C. glabrata strains entirely insensitive to histatin 5 (IC [50] [more than] 225 mega/ml). Four genetically very similar species to C. glabrata, Candida castelli, Saccharomyces cerevisiae, Kluyveromyces delphensis and Kluyveromyces bacillisporus were all sensitive to histatin 5 (IC [50] values between 2.6 and 64.6 mega/ml). C. glabrata was also insensitive to other members of the histatin family, histatin 1, 3, and P-113 (IC [50] values in all cases [more than] 225 mega/ml). In addition, two entirely different cationic antifungal proteins originating from frog skin, PGLa and magainin 2 also showed a strong reduced activity toward this fungus.
Next, our studies focused on the elucidation of the resistance mechanism of C. glabrata toward cationic antifungal proteins. While magainins and histatins differ in their presumed mode of action, they share a net positive charge and hence the first focus was on potential differences in cell surface properties of C. albicans and C. glabrata. The cell surface charge and the cytoplasmic transmembrane potential of C. albicans and C. glabrata were found to be very similar, indicating that these parameters cannot readily explain C. glabrata resistance to cationic antifungal proteins. One way by which C. glabrata could achieve resistance is through the secretion of a component which would neutralize the activity of the antifungal protein. To investigate this possibility, histatin stability and histatin antifungal activity were studied in C. albicans and in C. glabrata supernatants. Histatin 5 was enzymatically degraded in some fungal cell supernatants, but no correlation was found between histatin stability and the antifungal susceptibility of the respective fungal strain. Interestingly, when the antifungal activity was considered, it was found that histatin 5 activity toward C. albicans was strongly reduced in the presence of C. glabrata supernatants. This result suggests that C. glabrata secretes a component, albeit not a protease, that counteracts the activity of histatins.
In conclusion, besides the well-described inherent resistance of C. glabrata to azole-derived antifungal agents, our studies indicate that this species is also able to withstand the otherwise detrimental activities of cationic antifungal proteins. Charge differences at the membrane level did not explain the resistance of C. glabrata to cationic antifungal proteins. However, C. glabrata cells appear to secrete factors that interfere with histatin 5 antifungal activity. Future studies aimed at elucidating these factors could shed light not only on the mechanism of antifungal resistance of C. glabrata, but also on critical pathways in the killing mechanism of C. albicans.
Description
PLEASE NOTE: This work is protected by copyright. Downloading is restricted to the BU community: please click Download and log in with a valid BU account to access. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.
Thesis (MSD)--Boston University, Goldman School of Dental Medicine, 2007 (Dept. of Periodontology and Oral Biology).
Includes bibliographical references: leaves 95-108.
Thesis (MSD)--Boston University, Goldman School of Dental Medicine, 2007 (Dept. of Periodontology and Oral Biology).
Includes bibliographical references: leaves 95-108.
License
This work is protected by copyright. Downloading is restricted to the BU community. If you are the author of this work and would like to make it publicly available, please contact open-help@bu.edu.