Value of detection of antibodies to Candida albicans germ tube in the diagnosis of systemic candidosis

Diagnostic surveillance by Candida albicans germ tube antibody in intensive care unit patients

BACKGROUND

The diagnosis of Invasive Candidiasis (IC) presents serious problems, mainly associated with the absence of pathognomonic symptoms of the disease and the difficulty of isolating the fungus in blood culture. Candida albicans germ tube antibody (CAGTA) provides a rapid and simple test for diagnosis of IC. The aim of this study was to evaluate the diagnostic role of the CAGTA in the monitoring of critically-ill patients at risk of developing IC.

METHODS

During diagnostic surveillance in the intensive care units (ICU) CAGTA was performed twice a week if predetermined risk factors were present and a positive result was considered when a serum titer ≥1/160 was detected in at least one sample.

RESULTS

Seventy critically ill patients were included in the study. Twenty-three patients with proven/probable IC were identified. The sensitivity, specificity, PPV, and NPV of CAGTA for the diagnosis of proven/probable IC in all 70 patients were 91.3%, 68.1%, 58.3%, and 94.1%, respectively. Statistically significant highest titers were found in patients with proven/probable IC as well as increasing titers more than 1/160.

CONCLUSIONS

Our results suggest that detection of CAGTA could be a useful biomarker for the diagnosis of proven and probable IC in critical patients during prolonged ICU stay. During the monitoring it is opportune to evaluate the titers kinetics since the clinical diagnosis of proven/probable IC coincided with increase titer from negative (<1/160) to more than 1/160.

[Invasive fungal disease: conventional or molecular mycological diagnosis?]

Diagnosis of invasive mycoses is a difficult challenge due to the limitations and low sensitivity of traditional microbiology methods which lead to diagnostic and therapeutic delays. The aim of this review is to summarise the state of the art of the molecular diagnosis of invasive fungal disease and to clarify its current role in the clinical practice. Conventional microbiological methods could be complemented with molecular methods in the rapid and definitive identification of fungal isolates. Biomarkers (β-glucan, galactomannan) are very useful in immunocompromised patients and have been included as probable invasive mycoses by the EORTC/MSG. Nucleic acid detection is currently used as a complementary tool for diagnosis. However, PCR can be very useful in mould invasive mycoses. Finally, the combined detection using biomarkers can improve the diagnosis. However, their applicability in the microbiology laboratory is not so easy and further studies are required for the appropriate evaluation of its clinical usefulness.

Clinical factors associated with a Candida albicans Germ Tube Antibody positive test in Intensive Care Unit patients

BACKGROUND

Poor outcomes of invasive candidiasis (IC) are associated with the difficulty in establishing the microbiological diagnosis at an early stage. New scores and laboratory tests have been developed in order to make an early therapeutic intervention in an attempt to reduce the high mortality associated with invasive fungal infections. Candida albicans IFA IgG has been recently commercialized for germ tube antibody detection (CAGTA). This test provides a rapid and simple diagnosis of IC (84.4% sensitivity and 94.7% specificity). The aim of this study is to identify the patients who could be benefited by the use of CAGTA test in critical care setting.

METHODS

A prospective, cohort, observational multicentre study was carried out in six medical/surgical Intensive care units (ICU) of tertiary-care Spanish hospitals. Candida albicans Germ Tube Antibody test was performed twice a week if predetermined risk factors were present, and serologically demonstrated candidiasis was considered if the testing serum dilution was ≥ 1:160 in at least one sample and no other microbiological evidence of invasive candidiasis was found.

RESULTS

Fifty-three critically ill non-neutropenic patients (37.7% post surgery) were included. Twenty-two patients (41.5%) had CAGTA-positive results, none of them with positive blood culture for Candida. Neither corrected colonization index nor antifungal treatment had influence on CAGTA results. This finding could corroborate that the CAGTA may be an important biomarker to distinguish between colonization and infection in these patients. The presence of acute renal failure at the beginning of the study was more frequent in CAGTA-negative patients. Previous surgery was statistically more frequent in CAGTA-positive patients.

CONCLUSIONS

This study identified previous surgery as the principal clinical factor associated with CAGTA-positive results and emphasises the utility of this promising technique, which was not influenced by high Candida colonization or antifungal treatment. Our results suggest that detection of CAGTA may be important for the diagnosis of invasive candidiasis in surgical patients admitted in ICU.

Clinical significance of the detection of Candida albicans germ tube-specific antibodies in critically ill patients

The present study, comprising a prospective multicentre study including 53 non-neutropenic patients from intensive care units (ICU) in six Spanish tertiary-care hospitals, was carried out to determine the clinical significance and influence on mortality of Candida albicans germ tube-specific antibodies (CAGTA). There were 22 patients (41.5%) for whom the CAGTA results were positive, although none of had a blood culture positive for Candida. The intra-ICU mortality rate was significantly lower (p = 0.004) in CAGTA-positive patients (61.2% vs. 22.7%). Multivariate analysis confirmed that a positive CAGTA result was the only protective factor to be independently associated with ICU mortality (beta coefficient = -0.3856; 95% confidence interval = -0.648 to -0.123).

Use of recombinant antigens for the diagnosis of invasive candidiasis

Invasive candidiasis is a frequent and often fatal complication in immunocompromised and critically ill patients. Unfortunately, the diagnosis of invasive candidiasis remains difficult due to the lack of specific clinical symptoms and a definitive diagnostic method. The detection of antibodies against different Candida antigens may help in the diagnosis. However, the methods traditionally used for the detection of antibodies have been based on crude antigenic fungal extracts, which usually show low-reproducibility and cross-reactivity problems. The development of molecular biology techniques has allowed the production of recombinant antigens which may help to solve these problems. In this review we will discuss the usefulness of recombinant antigens in the diagnosis of invasive candidiasis.

Avances y limitaciones del diagnóstico precoz de las infecciones invasoras causadas por levaduras

In the last years, the main advances in the serological diagnosis of mycoses caused by yeasts have occurred in the area of antibody and (1-3)-beta-D-glucan detection. Commercialization of the Candida albicans IFA IgG test and detection of antibodies against recombinant antigens Hwp1 and enolase are the most important contributions to the first area. Detection of (1-3)-beta-D-glucan confirms its usefulness as a good marker for the diagnosis of invasive candidiasis. The most recent studies suggest that combination of two tests to detect antígen, antibodies, (1-3)-beta-D-glucan and DNA will be needed to optimize the diagnosis of systemic yeast infections.

Diagnosis of invasive candidiasis by enzyme-linked immunosorbent assay using the N-terminal fragment of Candida albicans hyphal wall protein 1

BACKGROUND

The diagnosis of invasive candidiasis is difficult because there are no specific clinical manifestations of the disease and colonization and infection are difficult to distinguish. In the last decade, much effort has been made to develop reliable tests for rapid diagnosis of invasive candidiasis, but none of them have found widespread clinical use.

RESULTS

Antibodies against a recombinant N-terminal fragment of the Candida albicans germ tube-specific antigen hyphal wall protein 1 (Hwp1) generated in Escherichia coli were detected by both immunoblotting and ELISA tests in a group of 36 hematological or Intensive Care Unit patients with invasive candidiasis and in a group of 45 control patients at high risk for the mycosis who did not have clinical or microbiological data to document invasive candidiasis. Results were compared with an immunofluorescence test to detect antibodies to C. albicans germ tubes (CAGT). The sensitivity, specificity, positive and negative predictive values of a diagnostic test based on the detection of antibodies against the N-terminal fragment of Hwp1 by immunoblotting were 27.8 %, 95.6 %, 83.3 % and 62.3 %, respectively. Detection of antibodies to the N-terminal fragment of Hwp1 by ELISA increased the sensitivity (88.9 %) and the negative predictive value (90.2 %) but slightly decreased the specificity (82.6 %) and positive predictive values (80 %). The kinetics of antibody response to the N-terminal fragment of Hwp1 by ELISA was very similar to that observed by detecting antibodies to CAGT.

CONCLUSION

An ELISA test to detect antibodies against a recombinant N-terminal fragment of the C. albicans germ tube cell wall antigen Hwp1 allows the diagnosis of invasive candidiasis with similar results to those obtained by detecting antibodies to CAGT but without the need of treating the sera to adsorb the antibodies against the cell wall surface of the blastospore.

Anticuerpos anti-micelio de Candida albicans en dos pacientes de cuidados intensivos con candidiasis invasora

Two cases of invasive candidiasis in intensive care patients are presented to illustrate the usefulness of detection of antibodies to Candida albicans germ tubes in the diagnosis of invasive candidiasis and in monitoring the efficacy of the antifungal treatment.

El diagnóstico microbiológico independiente del cultivo en la candidiasis invasora. Importancia de los marcadores fúngicos

The usefulness of surrogate markers in the diagnosis of invasive candidiasis is based on their ability to detect the infection caused by the different Candida spp. and to differentiate when the fungus is a colonizer or it is causing an invasive disease. This differentiation has been tried by detecting antigens, antibodies and other Candida components in the patient's sera. In this paper we will review the antigens, antibodies and other Candida components which may be useful in the laboratory diagnosis of invasive candidiasis in the non-neutropenic critically ill patient.

[Evaluation of a new commercial test (Candida albicans IFA IgG) for the serodiagnosis of invasive candidiasis]

INTRODUCTION

Two tests for the detection of antibodies to Candida albicans germ tubes in patients with invasive candidiasis were compared: a new commercially available test (Candida albicans IFA IgG) and the indirect immunofluorescence test generally used for this purpose.

METHODS

With the use of two indirect immunofluorescence tests, retrospective study was done on 172 sera from 51 patients classified into two groups: Group I included 123 serum samples from 32 patients with invasive candidiasis, and Group II, the control, included 49 serum samples from 19 patients with no evidence of Candida infection.

RESULTS

In Group I, 84% of patients presented anti-germ tube antibody titers >or= 1:160 by the Candida albicans IFA IgG test and 78.1% of patients were positive by the generally used test. There was a high correlation between the two tests (R2 =0.9512 by patients; R2 = 0.8986 by sera). When a titer value of >or= 1:160 was used as cutoff, the Candida albicans IFA IgG test showed a sensitivity of 84.4% and a specificity of 94.7%, whereas the traditional test showed a sensitivity of 78.1% and a specificity of 100%.

CONCLUSIONS

The commercially available Candida albicans IFA IgG test is similar to the test generally used for the detection of antibodies to C. albicans germ tubes and provides faster and easier diagnosis of invasive candidiasis in the clinical microbiology laboratory.

Recomendaciones para el diagnóstico micológico y estudios de sensibilidad a los antifúngicos

The guidelines presented herein, which are based on the indications established by various studies and expert opinions, analyze several issues related to laboratory diagnosis of invasive fungal infections in immunosuppressed patients.

The detection of anti-Candida antibodies on experimental animal models

The levels of anti-Candida antibodies were determined in experimental animals immunized with 4 different yeast doses (0.3, 0.6, 1.2, 2.4 x 10(8) CFU) at weekly intervals. After immunization (sampling intervals 1, 2, and 3 months), the intravenous blood was examined for the presence of serum anti-Candida antibodies. After one month, the titers of anti-Candida antibodies reached 1:40-1: 1280 and remained at the same level after two months in the majority of animals; only in a few of them the titers increased or were detected de novo. After three months, when the animals were no longer immunized, a decreasing trend in antibody titers was detected in the majority of animals.

Semi-quantitative adsorption for detection of antibodies to Candida albicans germ tubes by indirect immunofluorescence test

Adsorption of antibodies against antigens expressed on the Candida albicans blastoconidia cell walls was standardized for the detection of antibodies to germ tubes by an indirect immunofluorescence test (IIFT). Sera from rabbits immunized with C. albicans bearing germ tubes, were diluted by two-fold serial dilutions to obtain specimens 1 : 640-1 : 20 positive by IIFT. Different volumes of specimens were adsorbed with different amounts of whole, heat-inactivated C. albicans blastoconidia. It was found that a 1 : 640 titre serum should be adsorbed at 30 microl by 50 mg cells, down to a 1 : 20 titre serum at 110 microl by 12.5 mg cells. Accurate detection of anti-germ tube antibodies by IIFT depends on the semi-quantitative relation between the positive titre of the specimen and the amount of blastoconidia used in adsorption.

Detection of anti-Candida antibodies in neonates from a Neonatal Intensive Care Unit

Anti-Candida antibodies were determined in a group of preterm neonates from a neonatal intensive care unit with serious diseases including candidemia. Antibodies to C. albicans blastospores, i.e. antibodies to C. albicans surface mannan and to C. albicans germ tubes were detected. Higher titers of antibodies to blastospores (1:320) occurred in all patients examined while antibodies to C. albicans germ tubes (with the highest titer of 1:160) were present in 32 out of 66 neonates examined. The highest titers of both anti-C. albicans blastospore antibodies and anti-C. albicans germ tube antibodies were detected in neonates with candidemia and disorders of saccharide metabolism.

Detection of anti-Candida antibodies by the indirect immunofluorescence assay in patients with cancer in the orofacial region

An indirect immunofluorescence assay was performed to detect antibodies to Candida albicans blastospores and germ tubes. Serum specimens were obtained from 82 patients with neoplastic diseases in the orofacial region and thrush of the oral mucosa. C. albicans was identified in the oral cavity of 63 patients investigated but serum anti-Candida antibodies were detected in only 23 of them. Serological examination showed that titers of antibodies to C. albicans blastospores ranged from 1:20 to 1:1280. High titers from 1:640 to 1:1280 were detected in patients without antibiotic, cytostatic, or radiotherapeutic treatment. The titers of antibodies to C. albicans germ tubes ranged from 1:20 to 1:640. Our results indicate that titers of antibodies to the C. albicans germ tubes were lower and were detected in a smaller number of patients.

The utility of serology in diagnosing candidosis in non-neutropenic critically ill patients

This study was carried out to evaluate the utility of serological tests in the diagnosis of candidal infections in non-neutropenic critically ill patients. A prospective study was carried out in a 10-bed general intensive care unit; all patients with at least one organic sample with Candida spp. were included. A therapeutic-diagnostic algorithm was designed, and patients were treated or not, according to a classification. Blood samples were taken, and serological tests included: antigenaemia detection using two different commercial latex kits (Cand-Tec and Pastorex) and antibody detection by indirect haemagglutination (IHA) and indirect germ tube immunofluorescence (IFA). A total of 56% of antibody tests (IHA 45% and IFA 64%) and 26% of antigen tests (Cand-Tec 36% and Pastorex 17%) were positive. The sensitivity and specificity of these tests with respect to systemic candidosis were 37% and 78%, respectively, for antibodies, and 0% and 90% for antigens. There was statistical significance for mortality and low levels of antibodies; Candida glabrata was detected by IFA and Candida tropicalis by Cand-Tec. Serological tests may help to define the prognosis of these patients and to support the detection of specific Candida species.

Use of monoclonal antibody in diagnosis of candidiasis caused by Candida albicans: detection of circulating aspartyl proteinase antigen

To develop a serological diagnosis of invasive candidiasis based on detection of circulating secreted aspartyl proteinase (SAP) antigen of Candida albicans, three different enzyme-linked immunosorbent assays (ELISAs) were compared. The first was a standard ELISA to detect anti-SAP antibodies, and the others were an antigen capture ELISA and an inhibition ELISA to detect circulating SAP antigen with monoclonal antibody (MAb) CAP1, which is highly specific for SAP. These tests were applied to 33 serum samples retrospectively selected from 33 patients with mycologically and/or serologically proven invasive candidiasis caused by C. albicans. Serum samples from 12 patients with aspergillosis and serum samples from 13 healthy individuals were also included. The sensitivities and specificities were 69.7 and 76.0% for the standard ELISA and 93.9 and 92.0% for the antigen capture ELISA, respectively. However, these values reached 93.9 and 96.0%, respectively, for the inhibition ELISA. Serum samples from 31 of 33 patients had detectable SAP antigen, with concentrations ranging from 6.3 to 19.0 ng/ml. These results indicate that the inhibition ELISA with MAb CAP1 is effective in detection of circulating SAP antigen and that this assay may be useful for diagnosis and treatment monitoring of invasive candidiasis.

Low levels of antigenic variability in fluconazole-susceptible and -resistant Candida albicans isolates from human immunodeficiency virus-infected patients with oropharyngeal candidiasis

Three serial isolates of Candida albicans were obtained by direct swab or by oral saline rinses from each of five human immunodeficiency virus-infected patients with recurrent oropharyngeal candidiasis. Genotyping techniques confirmed the presence of a persistent strain in multiple episodes from the same patient, which was different from the strains isolated from other patients. Fluconazole susceptibility was determined by both an agar dilution method and the National Committee for Clinical Laboratory Standards macrobroth procedure. In four of these patients the strains developed fluconazole resistance, and in one patient the strain remained susceptible. The different isolates were propagated as yeast cells on a synthetic medium, and their cell wall proteinaceous components were extracted by treatment with beta-mercaptoethanol. Protein and mannoprotein components present in the extracts were analyzed by electrophoresis, immunoblotting, and lectin-blotting techniques. The analysis showed a similar composition, with only minor qualitative and quantitative differences in the polypeptidic and antigenic patterns associated with the cell wall extracts from serial isolates from the same patient, as well as those from different strains isolated from different patients. Use of monospecific antibodies generated against two immunodominant antigens during candidiasis (enolase and the 58-kDa fibrinogen-binding mannoprotein) demonstrated their expression in all isolates tested. Overall, the antigenic makeup of C. albicans strains remained constant during the course of infection and was not affected by development of fluconazole resistance. In contrast to previous reports, the low degree of antigenic variability observed in this study may be due to the fact that the isolates were obtained from a highly homogeneous population of patients and to the uniformity in techniques used for the isolation, storage, and culture of the different strains, as well as extraction methodologies.

Characterization of Candida albicans antigenic determinants by two-dimensional polyacrylamide gel electrophoresis and enhanced chemiluminescence

The use of a two-dimensional polyacrylamide gel electrophoresis joined with Western blotting allowed us to investigate the reactivities of antibodies present in sera from mice and humans to antigens of Candida albicans blastoconidia. The analysis of the antibody response in the two models studied and the comparison between the antibody response in infected and noninfected individuals showed that the infection by C. albicans produces changes in the antibody response which may be of relevance in the serodiagnosis of invasive candidiasis. These changes include the induction of antibodies against new antigens, the disappearance of antibodies against a group of antigens and variations in the reactivity of antibodies directed to a different group of antigens. The technique used resolved the isoforms of several antigens including enolase. It is concluded that the antibody response in humans and mice with candidiasis is not homogeneously directed to all the isoforms of an antigen.

Detection of antibodies to Candida albicans germ tubes during experimental infections by different Candida species

Identification and characterization of Candida albicans germ tube-specific antigens may be of relevance for the serodiagnosis of invasive candidiasis since they could be the basis for the development of new diagnostic tests. In this study, we have identified two antigens of 180 and >200 kDa in the cell wall of C. albicans germ tubes which are responsible for the induction of antibodies to C. albicans germ tubes. Antigens of similar molecular masses have been demonstrated in the cell walls of the Candida species C. stellatoidea, C. parapsilosis, C. guilliermondii, C. tropicalis, and C. krusei, but not C. glabrata. The kinetics of the antibody responses to C. albicans germ tubes were studied in rabbits infected with different Candida species. Although these antibodies were detected in rabbits infected with all Candida species except C. glabrata, the kinetics of the antibody responses to C. albicans germ tubes induced by the Candida species studied were different. Both the highest titer and the earliest response of antibodies to C. albicans germ tubes were observed in rabbits infected with either of the two serotypes of C. albicans used. However, the time needed to elicit the antibodies to C. albicans germ tubes can be reduced as the result of an anamnestic antibody response. The results presented in this study show that a test designed to detect antibodies against C. albicans germ tube antigens may be suitable for the diagnosis of infections caused by most of the medically important Candida species.

Serologic response to cell wall mannoproteins and proteins of Candida albicans

The cell wall of Candida albicans not only is the structure in which many biological functions essential for the fungal cells reside but also is a significant source of candidal antigens. The major cell wall components that elicit a response from the host immune system are proteins and glycoproteins, the latter being predominantly mannoproteins. Both the carbohydrate and protein moieties are able to trigger immune responses. Although cell-mediated immunity is often considered to be the most important line of defense against candidiasis, cell wall protein and glycoprotein components also elicit a potent humoral response from the host that may include some protective antibodies. Proteins and glycoproteins exposed at the most external layers of the wall structure are involved in several types of interactions of fungal cells with the exocellular environment. Thus, coating of fungal cells with host antibodies has the potential to influence profoundly the host-parasite interaction by affecting antibody-mediated functions such as opsonin-enhanced phagocytosis and blocking the binding activity of fungal adhesins for host ligands. In this review, the various members of the protein and glycoprotein fraction of the C. albicans cell wall that elicit an antibody response in vivo are examined. Although a number of proteins have been shown to stimulate an antibody response, for some of these species the response is not universal. On the other hand, some of the studies demonstrate that certain cell wall antigens and anti-cell wall antibodies may be the basis for developing specific and sensitive serologic tests for the diagnosis of candidasis, particularly the disseminated form. In addition, recent studies have focused on the potential for antibodies to cell wall protein determinants to protect the host against infection. Hence, a better understanding of the humoral response to cell wall antigens of C. albicans may provide the basis for the development of (i) effective procedures for the serodiagnosis of disseminated candidiasis and (ii) novel prophylactic (vaccination) and therapeutic strategies for the management of this type of infection.

Candiduria in non-neutropenic critically-ill surgical patients. Detection of IgA, IgG and IgM antibodies to Candida albicans by germ tube immunofluorescence

The significance of indirect immunofluorescence using Candida albicans germ tube as well as blastospore antigens in the diagnosis of isolated candiduria in non-neutropenic, critically-ill surgical patients was assessed. Ten patients with isolated candiduria, 12 with systemic candidosis and 10 with multifocal muco-cutaneous candidosis were included in the study. The sera of another 10 critically-ill patients with no signs of candidosis served as controls. The patients' sera were tested for IgG, IgA and IgM antibodies. The results obtained confirmed that indirect germ tube immunofluorescence is a useful procedure for differentiating systemic candidosis from colonisation of the urinary tract. Indirect immunofluorescence with blastospores, although more sensitive than germ tube immunofluorescence, cannot distinguish muco-cutaneous candidosis from systemic candidosis. Therefore, indirect germ tube immunofluorescence is regarded a useful complementary test to evaluate candiduria in non-neutropenic, HIV-negative, critically ill patients.

Detection of antibodies to Candida albicans germ tubes for diagnosis and therapeutic monitoring of invasive candidiasis in patients with hematologic malignancies

We prospectively investigated the ability of detection of antibodies to Candida albicans germ tubes (CAGT) to diagnose invasive candidiasis in 95 consecutive admissions of 73 patients with hematologic disorders undergoing intensive chemotherapy. The episodes were divided into three groups according to clinical and microbiological diagnosis. Group 1 comprised eight admissions of eight patients with invasive candidiasis. Group 2 comprised 42 admissions of 34 patients without evidence of invasive candidiasis. Group 3 comprised the remaining 45 admissions of 37 patients with febrile episodes which were not diagnosed by microbiological culture. Antibodies to CAGT were detected in 87.5% of group 1 patients. Detection of antibodies to CAGT in patients with Candida fungemia was delayed somewhat relative to the time the blood culture was positive, but antibodies to CAGT were detected earlier than a diagnosis was made in patients with deep-tissue candidiasis. Sera from 2 admissions in group 2 and 12 admissions in group 3 revealed antibodies to CAGT. At a titer of > or = 1:20, detection of antibodies to CAGT had a sensitivity of 87.5%, specificity of 95.2%, positive predictive value of 77.8%, and negative predictive value of 97.6%. Antibodies to CAGT were usually detected before beginning of empiric antifungal therapy. Titers of antibodies to CAGT were maintained in most patients who died but declined and eventually disappeared in the patients who survived. Since antibodies to CAGT were detected in all patients with tissue-proven invasive candidiasis but negative by blood culture, detection of antibodies to CAGT complemented blood cultures for diagnosis and therapeutic monitoring of patients with hematologic malignancies and invasive candidiasis.

Clinical and laboratory diagnosis of invasive candida infection in neutropenic patients

Cancer patients, especially those with acute leukaemia, represent a group that has the greatest risk for deep fungal infection. Almost no cases were seen before the advent of modern chemotherapy, and prior to the availability of antibacterial agents, less than 5% of patients with acute leukaemia died of fungal infection. These infections are now responsible for 40% or more of the deaths at some institutions. Candida species continues to be the most common fungal pathogen. Rapid and specific diagnosis of invasive candiosis enabling early effective therapy is therefore an important measure for reducing mortality in patients. Here the current status of clinical and laboratory diagnosis of invasive candida infection in neutropenic patients is discussed and recommendations made as to future development programmes.

Re-expression by Candida albicans germ tubes of antigens lost during subculture of blastospores

The effect of germ tube induction on the antigenic variability in C.albicans was studied in strains from blood cultures (Group I) and superficial candidiasis (Group II). When compared by immunoblotting with a rabbit antiserum, antigenic extracts from Group I strains grown as blastospores showed a higher reactivity than that of Group II strains. Major bands in Group I strains (45-47, 33, 30 kDa) were continuously expressed through the subcultures in vitro but, with the exception of the 45 kDa band, the reactivity of all of them decreased or disappeared after the tenth subculture in Group II strains. The induction of the germ tubes produced the re-expression of the antigens lost during subculture in the yeast form, the effect being very clear in Group II strains. The re-expression by C. albicans germ tubes of antigens lost during subculture of blastospores in vitro and the higher reactivity shown by Group I strains grown in mycelial phase should be taken into consideration when a test to detect anti-C. albicans antibodies is to be developed.

Kinetics of anti-mannan antibodies useful in confirming invasive candidiasis in immunocompromised patients

In studying the anti-mannan antibodies longitudinally in serial serum samples of three immunocompromised patients, it was observed that anti-mannan antibodies started to increase shortly after the moment that cultures of deep-tissue sites became positive with Candida albicans. The mean anti-mannan antibody titers determined in a group of 36 immunocompromised patients with invasive candidiasis increased within two weeks after the probable onset of invasive candidiasis. In contrast, anti-mannan antibody levels in serial serum samples of 14 immunocompromised patients who were only colonized with C. albicans remained stable or decreased over time. The HA test measuring the anti-mannan antibodies was 64% sensitive and 89% specific in determining invasive candidiasis. In contrast, antibodies specific for candidal cytoplasmic antigens or enolase alone were of little value in confirming invasive candidiasis in these immunocompromised patients.

Purification of a Candida albicans germ tube specific antigen

In a previous work, Marot-Leblond et al. identified a Candida albicans germ tube-specific antigen by the use of a monoclonal antibody (mAb 3D9.3). In the present report, we used a two-step procedure to obtain a purified preparation of this antigen from a Zymolyase extract of Candida albicans germ tubes. The extract was first fractionated by gel filtration chromatography. The immunoreactive fractions were pooled, and the 3D9.3 antigen was further purified by hydrophobic interaction chromatography using a Phenyl-superose column. Analysis by SDS-PAGE, immunoblotting and Concanavalin A staining, revealed a single, polydisperse band ranging from 110 to 170 kDa. The antigen was purified 126-fold by protein content and 16.4-fold by carbohydrate content. Recovery of the antigen was 6.8% following the two-step purification.

Serodiagnosis of Penicillium marneffei infection

Diagnosis of Penicillium marneffei infection is often made late. We evaluated an indirect immunofluorescent antibody test for P marneffei in serum from 103 patients with persistent fever and from 78 normal subjects. Germinating conidia (initial tissue-invasion phase) and yeast-hyphae (tissue multiplication phase) forms were used as antigen. All 8 documented P marneffei cases (8%) had an IgG titre of 160 or more; the other 95 patients and all the healthy controls had an IgG titre of 40 or below. Blood culture was positive in only 1 case with HIV infection. Biopsy and culture of tissues were necessary for confirmation in the other 7 cases. The test could provide rapid presumptive diagnosis and supplement conventional culture.

Evaluation of three serological tests for detection of anti-candidal antibodies in diagnosis of invasive candidiasis

Immunoblot detection of antibody against 47 KD cytoplasmic antigen of Candida albicans was evaluated in diagnosis of invasive candidiasis and compared to whole cell agglutination and gel diffusion tests for detection of anticandidal antibody in 64 patients. The patients included 17 with culture proved candidemia, 34 with significant candiduria (more than 10,000 colony forming units per ml of urine) and 13 with nonsignificant candiduria. Antibody against 47 KD antigen was found to be the best indicator for diagnosis of invasive candidiasis even in patients with malignancy. The sensitivity of this procedure was 82.4%, specificity 86.7%, positive predictive value 77.8%, negative predictive value 89.7% and efficacy 85.1%. The gel diffusion procedure lacked in sensitivity whereas whole cell agglutination lacked in specificity. Detection of antibody against 47 KD antigen proved to be a valuable adjunct in the diagnosis of invasive candidiasis.

Simplified adsorption method for detection of antibodies to Candida albicans germ tubes

Two modifications that simplify and shorten a method for adsorption of the antibodies against the antigens expressed on both blastospore and germ tube cell wall surfaces (methods 2 and 3) were compared with the original method of adsorption (method 1) to detect anti-Candida albicans germ tube antibodies in 154 serum specimens. Adsorption of the sera by both modified methods resulted in titers very similar to those obtained by the original method. Only 5.2% of serum specimens tested by method 2 and 5.8% of serum specimens tested by method 3 presented greater than one dilution discrepancies in the titers with respect to the titer observed by method 1. When a test based on method 2 was evaluated with sera from patients with invasive candidiasis, the best discriminatory results (sensitivity, 84.6%; specificity, 87.9%; positive predictive value, 75.9%; negative predictive value, 92.7%; efficiency, 86.9%) were obtained when a titer of > or = 1:160 was considered positive.

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).

Diagnosis of invasive mycoses in severely immunosuppressed patients

In compromised patients, invasive mycoses are being observed at an increasing frequency and with a broadening spectrum of causative fungi. The rapid and definitive diagnosis of such opportunistic mycoses requires the synoptical consideration of predisposing clinical conditions, of culture isolates, and of the results of nonculture techniques. At present, the latter comprise the monitoring of specific antibodies and of fungal antigens, and the microscopical examination of suspected biopsies. The validity of the individual techniques (e.g., the monitoring of antibodies or antigens) varies with individual mycoses. Alternative methods for monitoring fungal metabolites or nucleic acids are still in the developmental stage. Particularly the amplification of DNA by the polymerase chain reaction (PCR) has a high diagnostic potential. However, at present, it is uncertain whether PCR allows the necessary distinction between colonization and truly invasive infection, and whether PCR can be simplified sufficiently to allow the continuous surveillance of high-risk patients.

Detection of antibodies to Candida albicans germ tube as a possible aid in diagnosing systemic candidiasis in bone marrow transplant patients

Indirect immunofluorescence assays to detect antibodies to Candida albicans blastospore and germ tube were performed in sera of 29 bone marrow transplant patients. Antibodies to germ tube were present in the sera of six patients, in four of whom a Candida albicans infection was highly probable, while in the other two patients it was not possible to determine the previous course. No healthy blood donors had these antibodies. On the other hand, detection of antibodies to Candida albicans blastospore showed low specificity in the diagnosis of systemic candidiasis. These preliminary findings suggest that the detection of antibodies to Candida albicans germ tube may be an important aid in the diagnosis of systemic candidiasis in bone marrow transplant patients.

Identification of antigens reacting with anti-Candida albicans germ tube antibodies

Anti-Candida albicans germ tube antibodies can be induced in rabbits immunized with different C. albicans extracts. Antigens responsible for the induction of those antibodies have molecular weights of approximately 230-250, 62, 43 and 41 kDa. These antigens are present in the cell wall of both C. albicans morphological forms, although their location seems to be different.

Candidal infection of bone. Assessment of serologic tests in diagnosis and management

In this case report, 30 sera from a 25-year-old heroin abuser with intervertebral candidosis were treated for the presence of anti-Candida albicans antibodies by agglutination, counterimmunoelectrophoresis, and indirect immunofluorescent assay. Sera were also adsorbed with heat-killed blastospores to remove antibodies against yeast-phase cells and tested by indirect immunofluorescent assay for anti-C. albicans germ tube antibodies (CAGTAs). Humoral responses to candidal 47-kD antigen were studied by immunoblotting in 23 unadsorbed sera. Anti-C. albicans antibodies were found in high titers by the three procedures but correlated poorly with the clinical evolution of the disease. CAGTAs were present from the beginning of the infection: Titers decreased in association with antifungal treatment and the patient's improvement, eventually becoming negative. Only class IgG antibodies to the 47-kD antigen were detected. These were present during the full course of the infection, failing to disappear at the end of the study. In this case, detection of CAGTAs appeared to be an important aid to diagnosis of the bony candidal infection, as they are detected early during the illness and seemed to have a prognostic significance.