Activity of caspofungin and voriconazole against clinical isolates of Candida and other medically important yeasts by the CLSI M-44A disk diffusion method with Neo-Sensitabs tablets.

In vitro activity of caspofungin and voriconazole against 184 clinical isolates of Candida and other medically important yeasts in comparison with that of fluconazole, ketoconazole, itraconazole and amphotericin B was determined by using a disk diffusion method (Neo-Sensitabs) standardized according to the recommendations of the CLSI documents M44-A and M44-S1 (same medium: Mueller-Hinton plus methylene blue; inoculum and minimal inhibitory concentration/zone breakpoints). Seventy-two percent of clinical isolates were susceptible to caspofungin, 23.6% showed an intermediate susceptibility (most of them were Candida parapsilosis) and 4.3% were resistant (values for Candida spp. were 71.2, 23.8 and 5%, respectively). For voriconazole, 96.7% of clinical isolates were susceptible and 3.3% were resistant (Candida spp.: 96 and 3.8%, respectively). Both caspofungin and voriconazole showed high activity against a wide variety of clinically important yeasts.

Antifungal agents: mode of action in yeast cells.

Different kinds of mycoses, especially invasive, have become an important public health problem as their incidence has increased dramatically in the last decades in relation to AIDS, hematological malignancies, transplant recipients and other immunosuppressed individuals. Management of fungal infections is markedly limited by problems of drug safety, resistance and effectiveness profile. Current therapy for invasive mycoses uses a relatively reduced number of antifungal drugs, such as amphotericin B, fluconazole and itraconazole. Other new antifungal agents from old and new chemical families, like voriconazole, posaconazole, ravuconazole, caspofungin and micafungin, have been introduced into the armamentarium for fungal infections management. This review is focused on the mode of action of those antifungal drugs used against pathogenic yeasts. The interaction of amphotericin B with ergosterol and other membrane sterols results in the production of aqueous pores of drug and the ergosterol biosynthetic pathway is the target of the allylamines, phenylmorpholines and azole antifungal agents. The main molecular target of azole antifungals is the cytochrome P-450 protein Erg11p/Cyp51p. Echinocandins, a new class of antifungal drugs, are fungal secondary metabolites that act against beta-1-3-D-glucan synthesis. The phenylmorpholines, of which amorolfine is the sole representative in human therapy, affect two targets in the ergosterol pathway: Erg24p (delta 14 reductase) and Erg2p (delta 8-delta 7 isomerase). The sordarins group are protein synthesis inhibitors that work by blocking the function of fungal translation elongation factor 2. Other protein inhibitors are zofimarin, BE31045, SCH57504, xylarin, hypoxysordarin and GR135402. In order to overcome the problems derived from the exploitation of azole drugs, macrolides and echinocandins, novel targets were explored. Proposed antifungal drugs have been developed against potential targets like the N-myristylation of fungal proteins, with inhibitors like myristate and histidine analogues or myristoylpeptide derivatives, aminobenzothiazoles, quinolines and benzofurans. Polymerization of cell wall carbohydrates from uridine di-phospho sugars is another potential target.

Effect of monoclonal antibodies directed against Candida albicans cell wall antigens on the adhesion of the fungus to polystyrene.

The adhesion of Candida albicans to polystyrene and the effect of three monoclonal antibodies (mAbs) reactive with C. albicans cell wall surface antigens on this process was assessed in vitro with several C. albicans strains. In the absence of mAbs, adhesion of C. albicans to polystyrene increased in parallel with germ-tube formation. However, the growth of the strains in the yeast phase at 25 degrees C or the use of an agerminative mutant inhibited adhesion to polystyrene. Serotype A and B strains showed similar kinetics of adhesion to polystyrene and no statistically significant differences in germination or adhesion were observed when strains from the two serotypes were compared. The three mAbs had different effects on both germination and adhesion of C. albicans. mAbs 3D9 showed no influence on either germination or adhesion to polystyrene in two C. albicans strains. mAb B9E decreased both adhesion (45.6%) and filamentation (52.6%), and mAb 21E6 decreased filamentation (34.0%) but enhanced adhesion by 23.3%. This enhancement was also observed with the agerminative mutant and it was dose-dependent. It was not related to the binding capacity of the MAb to polystyrene nor to an increase in cell surface hydrophobicity of the antibody-treated cells. In conclusion, both growth phases of C. albicans can adhere to polystyrene, although the conditions for this process seem to be different in each phase. The two types of adhesion of C. albicans to polystyrene might have a role in the colonization of medical implants. The disparate effects shown by mAbs directed against cell wall mannoproteins of C. albicans on the adhesion of the fungus to polystyrene should be taken into consideration when designing strategies to block the adhesion of C. albicans to plastic materials with mAbs.

Characterization of Candida albicans cell wall antigens with monoclonal antibodies.

The antigenic composition of Candida albicans is very complex. In order to study the antigenic relationship between blastoconidia and germ tubes of C. albicans, we produced several monoclonal antibodies and analyzed their reactivity against cell wall antigens either in intact cells or in cells treated with dithiothreitol. Overall, four types of reactivity were found. Monoclonal antibodies 3D9 and 15C9 stained the germ tubes only when tested by indirect immunofluorescence. However, they showed a different reactivity by immunoblotting. Monoclonal antibody 3D9 reacted with antigens with molecular masses of > 200 and 180 kDa specifically expressed in the germ tube. Monoclonal antibody 15C9 reacted with antigens of 87, 50, and 34 kDa present in the germ tube extract and with antigens of 92, 50, 34, and 32 kDa present in the blastoconidium extract. The reactivity of blastoconidia treated for different times with dithiothreitol with these monoclonal antibodies was also studied by enzyme-linked immunosorbent assay. The reactivity of monoclonal antibody 3D9 did not significantly change during the cell wall extraction. However, the reactivity of monoclonal antibody 15C9 was increased for blastoconidia extracted for 60 min and decreased markedly for blastocondia extracted for 120 min. Monoclonal antibody G3B was nonreactive by indirect immunofluoresence but reacted with antigens of 47 and 38 kDa present in the germ tube extract and with an antigen of 47 kDa present in the blastoconidium extract. Monoclonal antibody B9E stained both morphological phases by indirect immunofluorescence. By immunoblotting, it reacted with antigens of > 70 kDa present in the germ tube extract and with antigens of > 63, 56, 47, and 38 kDa present in the blastoconidium extract. Based on the results presented in this study, four types of antigens are described. Type I antigens are expressed on the outermost layers of the germ tube cell wall only. Type II antigens are expressed both on the germ tube cell wall surface and within the blastoconidium cell wall. Type III antigens are found within the cell wall of both blastoconidia and germ tubes. Type IV antigens are expressed on both the blastoconidium and germ tube surface. Two types more can be hypothesized for antigens expressed on the blastoconidium cell surface and within the germ tube cell wall (type V) and for those expressed on the blastoconidium surface only (type VI).

Chitin assay to estimate the growth of Candida albicans in organs of infected mice.

Two methods have been used to estimate chitin. In both, the chitin was first converted into chitosan. The insoluble chitosan was then either depolymerized and deaminated with HNO2 and the product colorimetrically determined with 3-methylbenzo-2-thiazolone hydrazone and Fe3+ (method A), or hydrolysed in HCl and the glucosamine determined with p-dimethylaminobenzaldehyde (method B). Method B showed a better correlation between chitin concentration and absorbance, and its reliability was higher. This method was equally convenient to estimate the chitin content of germ tubes of Candida albicans grown in vitro, showing good correlation between mycelial growth and chitin content. Finally, method B was used to measure the growth of C. albicans in organs of animals infected experimentally.