Candida albicans group A-specific soluble antigens demonstrated by quantitative immunoelectrophoresis

Evaluation of latex reagents for rapid identification of Candida albicans and C. krusei colonies

A total of 322 yeast strains and yeastlike organisms belonging to the genera Candida, Cryptococcus, Geotrichum, Saccharomyces, and Trichosporon were tested with the new monoclonal antibody-based Bichro-latex albicans and Krusei color latex tests. Comparison of results with those obtained by conventional identification methods showed 100% sensitivity for both latex tests and 100% and 95% specificity for the Bichro-latex albicans and Krusei color tests, respectively. Because the test is easy to read and quick to perform, the Bichro-latex albicans test may be useful for rapid identification of Candida albicans colonies in the clinical laboratory.

Candida albicans serotype analysis by flow cytometry

Candida albicans strains can be assigned to either of two major serogroups, A or B. Antigenic surface determinants present only in serotype A strains allow such a distinction, which has epidemiologic relevance. Reports have established that the relative distributions of the two serotypes can vary depending on the geographic origin of the isolates. A prevalence of susceptibility to an antifungal agent, flucytosine, was also observed with isolates of serotype A. More recently, it was suggested that the occurrence of serotype B isolates in various clinical forms of candidiasis is increasing. However, this latest finding remains controversial since serotyping results vary widely from one laboratory to another because of the lack of standardized methodologies. Difficulty in interpretation of results, which may lead to erroneous serotype identification, is the major setback associated with current methods. For this study, we thus devised a procedure that relies on flow cytometry and that may eliminate ambiguities in serotype determination. The validation of results was achieved with two types of serotype A-specific antisera, Iatron Factor 6 antiserum and an anti-C. albicans antiserum adsorbed on serotype B yeast cells. Agreement between results obtained with these two reagents was 100% with a wide array of Candida strains. These results confirmed the potential of the flow cytometric procedure as a reliable and reproducible method to establish the serotypes of C. albicans strains. Furthermore, some applications of this procedure to the epidemiological study of this human pathogen are presented.

Comparison between methods for serotyping of Candida albicans produces discrepancies in results

Serotyping of 101 clinical isolates of Candida albicans was done with two sets of Hasenclever original anti-Candida typing sera (HSN 1 and 2) and Iatron Candida Check factor 6 typing serum (IF6). The results of these two methods were compared with slide agglutination reactions of yeast with monoclonal antibody H9. Agglutination reactions with this antibody have been previously shown to correlate with serotype. Results indicate the following correlations: between HSN 1 and HSN 2 serotyping, 93% (kappa = 0.85; 95% confidence interval [CI], 0.70 to 0.99); between IF6 and HSN 1, 60% (kappa = 0.39, 95% CI, 0.19 to 0.58); and between IF6 and HSN 2, 74% (kappa = 0.77; 95% CI, 0.64 to 0.90). Results with HSN 1 and 2 antisera correlated with H9 reactivity at 85 and 89% (kappa = 0.88; 95% CI, 0.75 to 1.00; and kappa = 0.85; CI, 0.70 to 0.99, respectively), while agreement between IF6 and H9 reactivities was less than or equal to 64% (kappa less than or equal to 0.43; 95% CI, 0.14 to 0.60). Autoagglutination of yeast during IF6 serotyping occurred with 21 of the 101 (20.8%) yeast strains. In every case, these yeast strains were serotyped by the HSN methods without autoagglutination and were uniformly type B. This study implies that it may not be possible to make valid comparisons between studies which compare serotype prevalence unless the same methods are used to serotype the yeast. The practicality and utility of serotyping in epidemiological studies are discussed, as are some of the problems associated with the available methods.

A critical review of typing methods for Candida albicans and their applications

During the 1980s, a large number of typing methods for the strain differentiation of Candida albicans were described in the literature. Although these methods have been based on a variety of physiological and genetic markers, none is ideal. This review discusses the characteristics of an ideal typing method in terms of its typability, reproducibility, and discriminatory power. Ways of determining these characteristics are presented so that the available typing methods for Candida albicans can be objectively compared. Available typing methods for C. albicans include serotyping, morphotyping, resistotyping, biotyping, and killer yeast typing. Electrophoretic methods include immunoblotting, isoenzyme analysis, analysis of DNA restriction fragment length polymorphism, karyotyping, and the use of DNA probes. The application of these methods to epidemiological research, the investigation of outbreaks of disease, and the study of virulence is described. The potential impact of the phenomenon of phenotypic switching on the reproducibility of these typing methods is discussed. It is concluded that many of the available typing methods have not been adequately assessed by their developers and that several have only poor discriminatory power or reproducibility.

Diagnosis of systemic candidiasis: development of co-counterimmunoelectrophoresis

To improve the results of counterimmunoelectrophoresis for serological diagnosis of candidiasis, a new method was devised to characterize human sera precipitins: co-counterimmunoelectrophoresis. Cellulose acetate was chosen as the support in order to observe identity reactions between precipitin lines from serum systems run conjointly (thus, co-counterimmunoelectrophoresis). Different experimental antisera (anti-somatic and anti-cytoplasmic antigens and anti-whole fixed germ tube antisera) were tested for reactions of identity with sera from selected patients with systemic candidiasis caused by Candida albicans. The reaction of patient sera and anti-germ tube antiserum with a selected somatic antigen always resulted in an identity reaction as proven by the continuity of major precipitin lines. The precipitating system, named the co-specific precipitin line, involved polysaccharide antigens; it was not present in human control sera.

Evaluation of cross-reactions in Histoplasma capsulatum serologic tests

Cross-reactivity in Histoplasma serologic tests was evaluated by using sera from patients with histoplasmosis and other infections. Serum samples from 127 of 134 (95%) patients with histoplasmosis were judged positive by complement fixation tests, and 121 (90%) showed H bands, M bands, or both by immunodiffusion. Of these 134 patients, cross-reactions were seen to Blastomyces dermatitidis in 53 patients (40%), to Coccidioides immitis in 20 patients (16%), and to Aspergillus fumigatus in 3 patients (2%) by complement fixation. Serum samples from 5 of 99 patients (5%) with other fungal infections and from 5 of 46 patients (11%) with tuberculosis had M precipitin bands by the Histoplasma immunodiffusion test, whereas none of the 123 sera from patients with other bacterial, Mycoplasma, or viral infections showed H or M precipitin bands. In the complement fixation test, positive reactions were observed in 16 of 90 patients (18%) with other fungal infections, in 14 of 41 patients (34%) with tuberculosis, and in 18 of 105 patients (17%) with other bacterial, Mycoplasma, or viral infections. Positive reactions were seen by radioimmunoassay in 54 of 110 patients (49%) with other fungal infections, in 23 of 46 patients (50%) with tuberculosis, and in 35 of 123 patients (28%) with with other bacterial, Mycoplasma, or viral infections. These results demonstrate a wider range of cross-reactions in Histoplasma serology than has been previously recognized, and the cross-reactivity was greatest when observed by radioimmunoassay. Caution should be exercised in the interpretation of serologic data from patients with suspected fungal infections.

Antigenic variability of Candida albicans

The concepts of modern biology lead us to think that all structures are liable to continual changes. Ultrastructural and biochemical methods have been able to objectify such a dynamic in Candida albicans, an opportunistic yeast. A broad analysis of antigens is a reliable way to study the antigenic variations which concern this organism. Numerous information on somatic and metabolic antigens of C. albicans is available at the moment. Paradoxically, if one accepts studies dealing with dimorphism, very few works have shown antigenic variability of this species or investigated the mechanisms involved in such a variability. The few approaches done in this way tend to prove that it may be possible to link together the expression of particular antigens and the behavior of the yeast, particularly when it acts as a pathogen.

Demonstration and solubilization of antigens expressed primarily on the surfaces of Candida albicans germ tubes

Antisera against mycelial-phase, but not yeast-phase, Candida albicans absorbed with yeast-phase organisms preferentially stained germ tube segments of several strains of mycelial-phase C. albicans by the indirect fluorescent-antibody staining technique. Germ tube segment antigens were not found in significant amounts on blastospore segments or on yeast-phase organisms. Absorption of the mycelial-phase reference sera with yeast-phase C. stellatoidea, but not with C. tropicalis, C. guillermondii, or Saccharomyces cerevisiae, resulted in preferential germ tube segment staining of C. albicans. A dithiothreitol extract of mycelial-phase C. albicans organisms blocked staining of the germ tube segment, but a dithiothreitol extract of yeast-phase organisms did not. When dithiothreitol extracts from both phases were reacted against yeast-absorbed reference sera in tandem crossed and crossed line immunoelectrophoresis, a cross-reacting arc and several arcs unique to the mycelial-phase extract were noted. Immunofluorescent staining tests were performed, using appropriately absorbed sera from patients with candidiasis to stain a laboratory strain of C. albicans. Human tissue slices infected with C. albicans were used as targets for appropriately absorbed rabbit antisera. These human data indicated that antigens preferentially expressed on the germ tube in vitro were also expressed on filamentous structures of the fungus in infected human tissues. In vitro and in vivo, the invasive mycelial phase of C. albicans expresses certain antigens that are highly concentrated on the germ tube.

Variability in expression of a cell surface determinant on Candida albicans as evidenced by an agglutinating monoclonal antibody

The expression of a surface immunodeterminant of Candida albicans was investigated with an agglutinating immunoglobulin M monoclonal antibody. The 96 strains of C. albicans tested, of which 76% were recent clinical isolates, were capable of expressing the antigen. The antigen was also produced by strains of Candida tropicalis and Torulopsis glabrata, but not by other yeast species. Expression of the surface immunodeterminant in C. albicans varied as a function of growth as indicated by agglutinin reactions and indirect immunofluorescence tests. When yeast cells were tested with the agglutinin, three patterns of reactivity were observed. In general, cells in the early logarithmic phase were less reactive than cells in the mid-logarithmic phase. Antigen expression, as determined by agglutinin reactivity, was also influenced by the nutritional composition of the growth medium, and in general, cells from broth cultures were usually more reactive than cells grown on solid media. The antigen was solubilized from the cell surface of C. albicans by hot 1 M NaCl. These water-soluble extracts were capable of binding antibody, and a single precipitin band formed when soluble antigen was reacted with the monoclonal antibody in an Ouchterlony double-diffusion test. Whole cell preparations and hot NaCl extracts from yeast strains which did not agglutinate when mixed with the antibody also did not absorb the agglutinin from solution. These data indicate that the expression of surface antigens on C. albicans is a dynamic process which may be influenced by a number of environmental factors. The use of monoclonal antibodies may allow characterization of surface antigens presented to the host during candidiasis.

Comparison of cytoplasmic extracts of eight Candida species and Saccharomyces cerevisiae

Crossed-line immunoelectrophoresis of cytoplasmic extracts of eight Candida species and Saccharomyces cerevisiae demonstrated the presence of antigens reactive with a rabbit antiserum to a C. albicans extract in all species except C. glabrata. A previously defined major cytoplasmic antigen of C. albicans was also present in C. tropicalis and C. guilliermondii.

Purification and characterization of a major cytoplasmic antigen of Candida albicans

In previous work (Jones, Infect, Immun. 30:78-89, 1980) a major cytoplasmic antigen of Candida albicans was identified. In both humans and experimental animals, this antigen is released from C. albicans during the course of an invasive C. albicans infection and elicits a specific antibody response. In this study, we used diethylaminoethyl cellulose chromatography and concanavalin A-Sepharose chromatography to obtain purified preparations of the major cytoplasmic antigen from crude cytoplasmic extracts of C. albicans. Column chromatography yielded a purified preparation of the major cytoplasmic antigen, which produced a single line in polyacrylamide gel electrophoresis. Using crossed immunoelectrophoresis, we detected small concentrations of contaminating antigens in the purified preparations. We found that the major antigen was a single polypeptide chain containing about 435 amino acid residues and had a molecular weight of 54,300. This antigen did not possess any of 19 common activities. Enzyme linked immunosorbent assays are being developed to detect this antigen in serum and to detect antibody against the antigen.