Increased arabinitol levels in experimental candidiasis in rats: arabinitol appearance rates, arabinitol/creatinine ratios, and severity of infection

Measurement of serum D-arabinitol/creatinine ratios for initial diagnosis and for predicting outcome in an unselected, population-based sample of patients with Candida fungemia

D-Arabinitol (DA) is a useful diagnostic marker for candidiasis in patients with neutropenia and other high-risk groups, but its use in unselected patients with a broad range of underlying diseases and conditions has not been studied. We used an automated enzymatic fluorometric assay to measure serum DA/creatinine ratios (DA/cr's) in 30 healthy adults, 100 hospitalized controls without Candida fungemia, and 83 patients from a study of all Candida fungemias in Connecticut between October 1998 and September 1999. Sixty-three of 83 (76%) fungemic patients and 11 of 100 (11%) nonfungemic controls had serum DA/cr's >or=3.9 microM/mg/dl (mean + 3 standard deviations for 30 healthy adults). High serum DA/cr's were less frequent in patients with cancer or fungemia caused by the DA nonproducer Candida glabrata than in patients with cancer or fungemia caused by a DA producer, C. albicans, C. tropicalis, or C. parapsilosis. The serum DA/cr was first >or=3.9 microM/mg/dl before, on the same day as, or after the first positive blood culture was drawn for 30 (36%), 22 (27%), and 11 (13%) fungemia patients, respectively. Mortality did not differ significantly among the patients with high or normal initial or peak serum DA/cr's, but mortality was higher if any serum DA/cr value was >or=3.9 microM/mg/dl 3 or more days after the onset of fungemia (18/27 versus 4/24 patients, respectively; P < 0.001). We conclude that serum DA/cr's are useful both for the initial diagnosis of Candida fungemia and for prognostic purposes for unselected patients with a broad range of underlying diseases and conditions.

Characterization of a novel NADP(+)-dependent D-arabitol dehydrogenase from the plant pathogen Uromyces fabae

We have identified and characterized a novel NADP(+)-dependent D-arabitol dehydrogenase and the corresponding gene from the rust fungus Uromyces fabae, a biotrophic plant pathogen on broad bean (Vicia faba). The new enzyme was termed ARD1p (D-arabitol dehydrogenase 1). It recognizes D-arabitol and mannitol as substrates in the forward reaction, and D-xylulose, D-ribulose and D-fructose as substrates in the reverse reaction. Co-factor specificity was restricted to NADP(H). Kinetic data for the major substrates and co-factors are presented. A detailed analysis of the organization and expression pattern of the ARD1 gene are also given. Immunocytological data indicate a localization of the gene product predominantly in haustoria, the feeding structures of these fungi. Analyses of metabolite levels during pathogenesis indicate that the D-arabitol concentration rises dramatically as infection progresses, and D-arabitol was shown in an in vitro system to be capable of quenching reactive oxygen species involved in host plant defence reactions. ARD1p may therefore play an important role in carbohydrate metabolism and in establishing and/or maintaining the biotrophic interaction in U. fabae.

Current status of nonculture methods for diagnosis of invasive fungal infections

The incidence of invasive fungal infections has increased dramatically in recent decades, especially among immunocompromised patients. However, the diagnosis of these infections in a timely fashion is often very difficult. Conventional microbiologic and histopathologic approaches generally are neither sensitive nor specific, and they often do not detect invasive fungal infection until late in the course of disease. Since early diagnosis may guide appropriate treatment and prevent mortality, there has been considerable interest in developing nonculture approaches to diagnosing fungal infections. These approaches include detection of specific host immune responses to fungal antigens, detection of specific macromolecular antigens using immunologic reagents, amplification and detection of specific fungal nucleic acid sequences, and detection and quantitation of specific fungal metabolite products. This work reviews the current status and recent developments as well as problems in the design of nonculture diagnostic methods for invasive fungal infections.

A rapid, automated enzymatic fluorometric assay for determination of D-arabinitol in serum

A rapid enzymatic fluorometric assay for measuring D-arabinitol in serum was developed using recombinant D-arabinitol dehydrogenase from Candida albicans (rArDH). rArDH was produced in Escherichia coli and purified by dye-ligand affinity chromatography. rArDH was highly specific for D-arabinitol, cross-reacting only with xylitol (4.9%) among all polyols tested. A Cobas Fara II centrifugal autoanalyzer (Roche) was used to measure NADH fluorometrically when rArDH and NAD were added to serum extracts, and D-arabinitol concentrations were calculated from standard curves derived from pooled human serum containing known amounts of D-arabinitol. The method was precise (mean intra-assay coefficients of variation [CVs], 0.8%, and mean interassay CVs, 1.6%) and rapid (3.5 min per assay) and showed excellent recovery of added D-arabinitol in serum (mean recovery rate, 101%). The mean and median D-arabinitol/creatinine ratios were 2.74 and 2.23 microM/mg/dl, respectively, for the 11 patients with candidemia compared to 1.14 and 1.23 microM/mg/dl, respectively, for 10 healthy controls (P < 0.01). These results confirm earlier studies showing that serum D-arabinitol measurement may help to promptly diagnose invasive candidiasis. The technique shows a significant improvement in terms of accuracy, cost, simplicity, specificity, and speed compared with gas chromatography, mass spectrometry, and earlier enzymatic assays.

D-arabinitol--a marker for invasive candidiasis

The five-carbon sugar alcohol D-arabinitol (DA) is a metabolite of most pathogenic Candida species, in vitro as well as in vivo, and can be determined by gas chromatography or enzymatic analysis. Endogenous DA and L-arabinitol (LA) are present in human body fluids, and serum DA and LA increase in renal dysfunction. In prospective clinical studies, elevated DA/LA or DA/creatine ratios in serum or urine have been found in immunocompromised, usually neutropenic, patients with invasive candidiasis. In addition, positive DA results have been obtained several days to weeks before positive blood cultures, and the normalization of DA levels has been correlated with therapeutic response in both humans and animals. However, to date, only a few prospective studies have been conducted in which adequate analytical methods were used. Thus, further investigation of various patient groups is needed to establish the applicability of the 'arabinitol method' in the diagnostic battery for invasive Candida infections.

Diagnosis and therapeutic monitoring of invasive candidiasis by rapid enzymatic detection of serum D-arabinitol

BACKGROUND

Using a rapid automated enzymatic assay, we prospectively investigated serum D-arabinitol (DA), a biochemical marker of invasive candidiasis, in a large population of high-risk patients to determine its potential diagnostic, therapeutic, and prognostic significance in invasive candidiasis.

PATIENTS AND METHODS

A total of 3,223 serum samples were collected from 274 patients with cancer. Serum DA concentrations were determined in coded serum samples analyzed by rapid enzymatic assay. Creatinine also was analyzed in the same system to determine a serum DA and creatinine ratio (DA/Cr). The sensitivity, specificity, correlation with therapeutic response, and prognostic significance were analyzed for all patient study groups.

RESULTS

A DA/Cr of > or = 4.0 mumol/L per mg/dL was detected in 31 (74%) of all 42 cases of fungemia and 25 (83%) of the 30 cases of the subset of persistent fungemia. Elevated DA/Cr was detected in 4 (40%) of 10 patients with tissue-proven, deeply invasive candidiasis and negative blood cultures (eg, hepatosplenic candidiasis or localized abscess) and 7 (44%) of 16 cases of deep mucosal candidiasis (eg, esophageal candidiasis). Elevated serial DA/Cr levels also were detected in persistently febrile and granulocytopenic patients requiring empirical amphotericin B. Among 26 assessable cases of fungemia, abnormally elevated DA/Cr values were detected in 14 (54%) before, 10 (38%) after, and 2 (8%) simultaneously with the first microbiologic report of fungemia. The trends of serial DA/Cr values correlated with therapeutic response in 29 (85%) of 34 patients with assessable cases of fungemia, decreasing in 8 (89%) of 9 patients with clearance of fungemia and increasing in 21 (84%) of 25 patients with persistence of fungemia. Among the 34 assessable patients with fungemia, mortality was directly related to the trend of serial DA/Cr determinations over time: 71% among fungemic patients who had persistently elevated or increasing DA/Cr, and 18% among the fungemic patients who had resolving DA/Cr or never had elevated DA/Cr (P < 0.01).

CONCLUSIONS

Rapid enzymatic detection of DA in serially collected serum samples from high-risk cancer patients permitted detection of invasive candidiasis, early recognition of fungemia, and therapeutic monitoring in DA-positive cases. Serially collected serum DA determinations complement blood cultures for improving detection and monitoring therapeutic response in patients at risk for invasive candidiasis.

D-arabitol metabolism in Candida albicans: construction and analysis of mutants lacking D-arabitol dehydrogenase

Candida albicans produces large amounts of the acyclic pentitol D-arabitol in culture and in infected animals and humans, and most strains also grow on minimal D-arabitol medium. An earlier study showed that the major metabolic precursor of D-arabitol in C. albicans was D-ribulose-5-PO4 from the pentose pathway, that C. albicans contained an NAD-dependent D-arabitol dehydrogenase (ArDH), and that the ArDH structural gene (ARD) encoded a 31-kDa short-chain dehydrogenase that catalyzed the reaction D-arabitol + NAD <=> D-ribulose + NADH. In the present study, we disrupted both ARD chromosomal alleles in C. albicans and analyzed the resulting mutants. The ard null mutation was verified by Southern hybridization, and the null mutant's inability to produce ArDH was verified by Western immunoblotting. The ard null mutant grew well on minimal glucose medium, but it was unable to grow on minimal D-arabitol or D-arabinose medium. Thus, ArDH catalyzes the first step in D-arabitol utilization and a necessary intermediate step in D-arabinose utilization. Unexpectedly, the ard null mutant synthesized D-arabitol from glucose. Moreover, 13C nuclear magnetic resonance studies showed that the ard null mutant and its wild-type parent synthesized D-arabitol via the same pathway. These results imply that C. albicans synthesizes and utilizes D-arabitol via separate metabolic pathways, which was not previously suspected for fungi.

Isolation, characterization and expression of the gene that encodes D-arabinitol dehydrogenase in Candida tropicalis

The gene (ARD) that encodes NAD-dependent D-arabinitol dehydrogenase (ArDH) in the pathogenic fungus Candida tropicalis (Ct) was cloned by transforming Escherichia coli (Ec) BW31M (araCc) with a plasmid library of Ct genomic DNA and selecting for D-arabinitol-utilizing (D-arab+) clones. Plasmid DNA from a D-arab+ clone retransformed fresh Ec BW31M cells to D-arab+; these cells produced both ArDH catalytic activity and a 31-kDa protein recognized by antibodies to native Ct ArDH. The plasmid contained an 846-bp open reading frame (ORF) that encoded a deduced protein of 282 amino acids (aa) (30,748 Da). Four partial aa sequences from Ct ArDH were present in the deduced aa sequence, thus verifying that Ct ARD had been cloned. Ct ArDH was 95% identical to ArDH from Candida albicans (Ca), 85% identical to a xylitol dehydrogenase (XDH) from Pichia stipitis (Ps) and 20-25% identical to many other short-chain dehydrogenases. Ct ArDH, Ca ArDH and Ps XDH were typical short-chain dehydrogenases except that they lacked an N-terminal Gly that is conserved in other members of this family. Thus, these enzymes may represent a subclass of closely-related fungal pentitol dehydrogenases. Large amounts of recombinant ArDH (re-ArDH) were produced in Ec and purified by dye ligand affinity chromatography. The physical and catalytic properties of re-ArDH were similar to those of native Ct ArDH, and re-ArDH and native ArDH performed similarly in an automated enzymatic assay for D-arabinitol in human serum.

Diagnosis and monitoring of disseminated candidiasis based on serum/urine D/L-arabinitol ratios

Disseminated candidiasis, a devastating disease with high morbidity and mortality in immunosuppressed patients, is difficult to diagnose because of the protean nature of symptoms and the lack of rapid and reliable laboratory diagnostic procedures. The subject of this review is the status of gas chromatographic-mass spectrometric techniques for the determination of D-arabinitol, a unique metabolite of pathogenic Candida species, in serum and urine. The enantiomers are separated by chiral chromatography followed by specific and sensitive detection using chemical ionization and selected ion monitoring. Using D/L-arabinitol ratios, instead of individual concentrations, eliminates the need for knowing the volume of samples and for calibration curves. A new filter paper technique requires only an unmeasured drop of whole blood (venous or finger/heel puncture) or urine; paper spots are mailable. Parallel determinations of D/L-arabinitol ratios in serum and urine in normal subjects and cancer patients with both normal and increased D/L-arabinitol ratios revealed constant (1.2-1.3 range) ratios of serum D/L-arabinitol/urine D/L-arabinitol for all populations studied. Analyzing two body fluids taken at the same time increases reliability by reducing false positives.

D-arabitol metabolism in Candida albicans: studies of the biosynthetic pathway and the gene that encodes NAD-dependent D-arabitol dehydrogenase

Candida albicans produces large amounts of the pentitol D-arabitol in culture and in infected mammalian hosts, but the functional and pathogenic significance of D-arabitol in C. albicans is not known. In this study, we sought to elucidate the pathway by which C. albicans synthesizes D-arabitol and to identify and characterize key enzymes in this pathway. C. albicans B311 produced D-[14C-1]arabitol from [14C-2]glucose; this finding implies on structural grounds that D-ribulose-5-PO4 from the pentose pathway is the major metabolic precursor of D-arabitol. NAD- or NADP-dependent pentitol dehydrogenases catalyze the final steps in D-arabitol biosynthesis in other fungi; therefore, lysates of C. albicans B311 were tested for enzymes of this class and were found to contain a previously unknown NAD-dependent D-arabitol dehydrogenase (ArDH). The ArDH structural gene was cloned by constructing a new D-arabitol utilization pathway in Escherichia coli. The C. albicans ArDH gene expressed in E. coli and Saccharomyces cerevisiae an enzyme that catalyzes the reaction D-arabitol + NAD <-->D-ribulose + NADH; this gene was present as a single copy per haploid genome, and its deduced peptide sequence was homologous with sequences of several members of the short-chain dehydrogenase family of enzymes. These results suggest that (i) C. albicans synthesizes D-arabitol by dephosphorylating and reducing the pentose pathway intermediate D-ribulose-5-PO4 and (ii) ArDH catalyzes the final step in this pathway.

Determination of serum arabinitol levels by mass spectrometry in patients with postoperative candidiasis

A combined gas chromatography-mass spectrometry (GC-MS) technique was used for serial determination of serum arabinitol levels in patients with postoperative candidiasis. Forty subjects were investigated, 18 patients with candidiasis, 7 patients with superficial Candida colonization and 15 postoperative control patients. The arabinitol levels were highly elevated, slightly elevated and normal in 13, 1 and 4 patients respectively with candidiasis; in 2, 2 and 3 colonized patients and in 1, 1 and 13 control patients (p < 0.001, chi 2, between all the groups). The sensitivity of a single arabinitol determination for detection of postoperative candidiasis was 27.6 % and the specificity 89.2 %. Use of multiple samples improved sensitivity up to 72.2% per patient (123 samples) with a specificity of 86.4 %. Highly elevated arabinitol concentrations were detected in only one patient before the onset of therapy. Determination of arabinitol levels by GC-MS is a specific test for diagnosing candidiasis, but multiple samples are required for adequate sensitivity, and the initiation of therapy must still be on an empirical basis.

Laboratory aids in the diagnosis of invasive candidiasis

The laboratory diagnosis of candidiasis continues to be problematic; however, there have been several advances in the past decade which promise to enhance our ability to identify patients at high risk for infection and/or to document invasive candidiasis in critically ill and immunocompromised patients. The introduction of commercially available biphasic blood culture medium and subsequently the lysis-centrifugation procedure has markedly improved the ability of laboratories to detect fungemia. Although serologic methods have not been very successful in diagnosing candidiasis in immunocompromised patients, several antigen detection methods are now under investigation. In addition, detection of fungal metabolites such as D-arabinitol remains promising. Finally, application of the techniques of molecular biology for typing and detection of fungal pathogens has expanded our understanding of candidal infections and may offer the most sensitive and specific means of diagnosing invasive candidiasis.

Production of the hexitol D-mannitol by Cryptococcus neoformans in vitro and in rabbits with experimental meningitis

We studied the ability of Cryptococcus neoformans to produce the hexitol D-mannitol in vitro and in rabbits with experimental meningitis. Twelve of twelve human isolates of C. neoformans produced D-mannitol in yeast nitrogen base plus 1% glucose and released D-mannitol into the medium. In a pilot study, pooled cerebrospinal fluid (CSF) from cortisone-treated rabbits given 3 x 10(7) C. neoformans H99 intracisternally contained more D-mannitol (identified by gas chromatography and enzymatically) than CSF from normal controls or cortisone-untreated rabbits with self-limited meningitis. In a second experiment, cortisone-treated rabbits given C. neoformans intracisternally had significantly higher CSF D-mannitol concentrations than controls given cortisone alone at 4, 6, and 8 days after infection. Moreover, log10 CSF D-mannitol correlated well with log10 CSF CFU (r = 0.81) and log10 CSF cryptococcal antigen titers (r = 0.78). Lastly, the initial volume of distribution and elimination half-life of D-mannitol given intracisternally to normal rabbits suggested that D-mannitol was distributed in total CSF and was removed by CSF bulk flow. Thus, C. neoformans produces D-mannitol in vitro and in vivo, and D-mannitol is a quantitative marker for experimental cryptococcal meningitis. D-Mannitol produced by C. neoformans may also contribute to brain edema and interfere with phagocyte killing by scavenging hydroxyl radicals.

Separation and quantification by gas chromatography-mass spectrometry of arabinitol enantiomers to aid the differential diagnosis of disseminated candidiasis

To differentiate increased arabinitol due to fungal (only D-arabinitol) and non-fungal origin, O-trifluoroacetyl derivatives of the enantiomers were separated using alpha-perpentylated cyclodextrin columns and measured by selected ion monitoring. Mean +/- S.D. D/L in normal serum: 1.40 +/- 0.42. D/L ratios greater than 2.24, defined as normal mean + 2S.D., were considered outside normal range. D/L was greater than 2.2 in 10 of 12 confirmed candidiasis cases with one false negative and one borderline. Renal dysfunction without candidiasis yielded normal D/L despite high arabinitol concentrations. D/L in normal urine was nearly identical to that in serum despite 60 times larger concentration. D/L ratios, determined by peak heights or areas, could be used without the need to determine concentrations.

Effects of gastrointestinal candidiasis, antibiotics, dietary arabinitol, and cortisone acetate on levels of the Candida metabolite D-arabinitol in rat serum and urine

We studied the effects of gastrointestinal (GI) colonization by Candida albicans, dietary arabinitol, intragastric antibiotics, and cortisone on levels of the Candida metabolite D-arabinitol in rat serum and urine. Rats given conventional laboratory chow, intragastric gentamicin and chloramphenicol, and 6.0 x 10(8) live C. albicans B311 blastoconidia by gavage had minimal invasive GI disease and no more DL-arabinitol in the urine than controls given killed C. albicans. However, colonized and uncolonized rats given intragastric antibiotics had transiently higher urine arabinitol levels than the corresponding controls given saline. Rats given conventional laboratory chow (which contained 50 micrograms of arabinitol per g) had higher serum and urine arabinitol levels than rats given no dietary arabinitol, but the differences were less than expected. Moreover, intragastric antibiotics did not cause increased arabinitol excretion in rats given no dietary arabinitol. Rats given intragastric antibiotics and live C. albicans but no dietary arabinitol had no more arabinitol in their serum or urine than controls given antibiotics and killed C. albicans or saline and live or killed C. albicans. Lastly, cortisone acetate (10 mg/kg of body weight per day intramuscularly for 10 days) did not cause increased serum or urine arabinitol levels. We conclude that neither GI colonization by C. albicans nor cortisone should interfere with the usefulness of arabinitol as a marker for invasive candidiasis; antibiotics appear to increase arabinitol excretion by suppressing GI bacteria capable of consuming dietary arabinitol.

Laboratory diagnosis of invasive candidiasis

Severe infections due to Candida species have become more frequent during the past two decades because of the increasing numbers of immunosuppressed patients being treated in our hospitals. Distinguishing colonization from invasive disease requires knowledge of the pathogenetic mechanisms leading to invasion. To assist the clinician in therapeutic decisions, clinical microbiologists should identify to species Candida organisms isolated from immunosuppressed patients. Quantitative or semiquantitative cultures of urine, burn tissues, intravascular catheter tips, and bronchoalveolar lavage specimens may provide useful information. Immunofluorescent staining of certain specimens can enhance diagnostic yield. The lysis-centrifugation blood culture technique offers some advantages over traditional broth techniques in detecting Candida fungemia. Antibody testing is of limited diagnostic value in highly immunosuppressed patients. Developing simple and reliable tests for detecting antigens or metabolites of Candida spp. in the sera of infected patients has proven difficult. Methods for typing Candida albicans are evolving. Typing should prove useful for studying the epidemiology of candidiasis in hospitalized patients.

Enantioselective measurement of the Candida metabolite D-arabinitol in human serum using multi-dimensional gas chromatography and a new chiral phase

A multi-dimensional gas chromatographic method was developed to measure the Candida metabolite D-arabinitol enantioselectively in human serum. The heptafluorobutyrate derivatives of D-arabinitol, L-arabinitol and ribitol (internal standard) were separated from other serum constituents with a 60 m X 0.32 mm fused-silica SPB-5 precolumn, and (after intermediate cold trapping) they were separated from each other with a 25 m x 0.25 mm fused-silica column coated with a new bonded chiral phase. Replicate analyses of spiked human sera showed that D-arabinitol could be quantified accurately and precisely. The D- and L-arabinitol concentrations in 24 normal adult sera were 0.20 +/- 0.053 and 0.11 +/- 0.040 mu/ml, respectively, and the D- and L-arabinitol/creatinine ratios were 0.023 +/- 0.011 and 0.012 +/- 0.0051, respectively (mean +/- S.D.). In a patient with Candida albicans fungemia, the D-arabinitol/creatinine ratios rose early during infection and fell with successful treatment, whereas L-arabinitol/creatinine ratios did not change significantly. This enantioselective analytical method is more practical than earlier ones; it should facilitate further investigation of D-arabinitol as a diagnostic marker for candidiasis.

In vitro susceptibilities of yeasts to a new antifungal triazole, SCH 39304: effects of test conditions and relation to in vivo efficacy

We used six candidal strains (two Candida albicans and one each of four other species) to study the effects of test conditions on the activity of SCH 39304 compared with that of fluconazole in broth macro- and microdilution assays. Increasing the inoculum from 10(2) to 10(5) yeasts per ml raised the MICs for all isolates up to greater than 512-fold. In contrast, results with a 50% turbidimetric endpoint (50% inhibitory concentration; IC1/2) varied no more than twofold. Similar effects were seen with fluconazole, and both drugs were found to have an associated delay in onset of action. Acidity was found to increase both MICs and IC1/2s. Other effects were observed among four synthetic media, but a consistent pattern was not identified. Incubation temperatures of 37, 35, and 30 degrees C yielded equivalent results. Broth microdilution IC1/2s against most of 40 isolates of C. albicans were 0.31 microgram/ml +/- fourfold for SCH 39304 and 0.16 microgram/ml +/- twofold for fluconazole. Treatment of experimental candidiasis in rats with SCH 39304 and fluconazole resulted in 50% effective doses of 0.33 and 0.49 mg/kg per day, respectively. In contrast, another C. albicans isolate, previously identified as resistant to other azoles, had IC1/2s of 20 micrograms of SCH 39304 per ml and, in vivo, a 50% effective dose of 2.25 mg/kg per day. We conclude that the in vivo efficacy of SCH 39304 correlates with MIC results when broth macrodilution testing is performed with a small inoculum and with IC1/2 results which are independent of inoculum size.

pH and other effects on the antifungal activity of cilofungin (LY121019)

We investigated the effects of various test conditions on broth macro- and microdilution susceptibility test results for several species of yeasts with a new antifungal agent, cilofungin. As the pH decreased from 7.4 to 3.0, 50% inhibitory concentrations (IC1/2) increased up to 64-fold. This effect was unrelated to yeast growth rate, solvent concentration, or choice of buffer. Broth microdilution results for 42 Candida albicans isolates at pH 7.4 in synthetic amino acid medium, fungal (SAAMF), showed IC1/2 results from 0.08 to 2.5 micrograms/ml, whereas at pH 3.0 the results were 5.0 or 10.0 micrograms/ml. Fungicidal concentrations were closer to MIC results at the lower pH, i.e., an average of 16-fold above the MIC at pH 3.0, compared with an average 256-fold difference at pH 7.4. Two strains that had very different IC1/2 results at pH 7.4 and identical IC1/2 results at pH 3.0 were found to be equally susceptible to cilofungin therapy in rats. In additional studies, other medium effects were demonstrable, with yeast nitrogen broth and minimal essential medium generally yielding higher results than two other synthetic media (SAAMF and RPMI 1640 medium). However, susceptibility results did not change with inoculum between 10(2) and 10(5) yeast cells per ml or temperature between 30 and 37 degrees C. These studies indicate that pH is an important influence on in vitro rank order susceptibility of pathogenic yeasts to cilofungin.

Enantioselective measurement of fungal D-arabinitol in the sera of normal adults and patients with candidiasis

A new method was used to measure D-arabinitol enantioselectively in the sera of 27 healthy adults and four patients with candidiasis. Arabinitol was measured by gas chromatography in serum that was treated with and without the Klebsiella pneumoniae enzyme D-arabinitol dehydrogenase, lactic dehydrogenase, NAD, and sodium pyruvate. Since enzyme treatment removed 98% of 0 to 20 micrograms of D-arabinitol per ml and none of 0 to 20 micrograms of L-arabinitol per ml from spiked sera, D-arabinitol could be determined from the difference in the treated and untreated samples. The concentrations of D- and L-arabinitol in serum from normal subjects were 0.22 +/- 0.052 and 0.16 +/- 0.055 micrograms/ml, respectively, and their D-arabinitol/creatinine and L-arabinitol/creatinine ratios were 0.024 +/- 0.0089 and 0.017 +/- 0.0053 (all means +/- standard deviations). The infected patients all had markedly elevated serum D-arabinitol levels, but their L-arabinitol levels were either normal or proportionately much lower. The excess arabinitol in the sera of individuals with candidiasis is D-arabinitol, and use of enantioselective analytical methods should result in improved ability to diagnose and estimate the severity of candidiasis.

Comparison of antibody, antigen, and metabolite assays in rat models of systemic and gastrointestinal candidiasis

We compared serial measurements of antibodies to mannan and to a cytoplasmic antigen (enzyme-linked immunosorbent assays), detection of mannan and an unidentified candidal antigen (latex agglutination), and assays of mannose and arabinitol (gas chromatographic assay of per-O-acetylated aldonitrile derivatives). In a high-inoculum intravascular-infection model, antimannan assays were consistently positive beginning on day 2 postinoculation, anti-cytoplasmic antigen assays followed the same time course but were less sensitive, mannan was detected in all samples beginning on day 2 postinoculation, and serum mannose concentrations peaked on day 3 postinoculation and were less sensitive than mannan detection. Other assays were not useful. In a lower-inoculum intravascular-infection model, the antibody assays became positive after a similar interval and remained positive for 28 days, with antimannan again being the more sensitive. Mannan and mannose tests were positive in week 1 postinoculation only, with mannan detection being the more sensitive. In a gastrointestinal-colonization model, antimannan assays become positive after 2 weeks of colonization, whereas anti-cytoplasmic antigen and mannan tests remained negative. In a model of gastrointestinal colonization followed by invasive infection produced by induction of neutropenia, only mannan detection was diagnostically useful. These data, comparing this panel of modern serodiagnostic techniques in controlled models of clinically relevant syndromes of candidiasis, enhance understanding of previous efforts in serodiagnosis of candidiasis and provide a foundation for further prospective studies in patients.

Diagnosis of invasive candidiasis in patients with and without signs of immune deficiency: a comparison of six detection methods in human serum

Visceral candidiasis in 56 patients, 39 of whom were thought to be immune deficient, was investigated using three serological detection methods--whole cell agglutination, haemagglutination, and counterimmunoelectrophoresis for antibodies; two determinations of circulating antigens--haemagglutination inhibition and latex agglutination; and determination of the arabinitol:creatinine ratio. Of the 39 patients with suspected immune deficiency, 13 had confirmed invasive candidiasis and 26 were colonised; of those without signs of immune deficiency, 10 patients also had invasive candidiasis and seven were colonised. Twenty three patients with invasive candidiasis were analysed in total. For suspected immune deficient patients the best discrimination between visceral candidiasis and colonisation was obtained by combining the results of haemagglutination inhibition and arabinitol:creatinine ratio. For patients without signs of immune deficiency the best discrimination between invasive candidiasis and colonisation was achieved with counterimmunoelectrophoresis. The results of the serological tests confirmed the classification on clinical grounds of those with and without immune deficiency.

Itraconazole treatment of experimental systemic candidiasis in male rats

After intravenous infection with Candida albicans, rats received daily doses of itraconazole for 3 days. All rats receiving 2.5 mg kg-1 day-1 survived while all rats receiving sham-treatment died. With subsequent reduction of the itraconazole dose to 0.63 mg kg-1 day-1, no survival occurred and mortality rates equalled those of the control group.

Activity of fluconazole (UK 49,858) and ketoconazole against Candida albicans in vitro and in vivo

Fluconazole (UK 49,858), a new orally administered bis-triazole, was compared with ketoconazole for activity in synthetic broth dilution susceptibility tests against Candida albicans and also in treatment of experimental systemic candidal infections in rats. In vitro studies indicated that fluconazole activity is less sensitive to acidic medium than is that of ketoconazole. At physiologic pH, fluconazole was approximately 16-fold less active than ketoconazole against 35 representative isolates of C. albicans. Two additional isolates (K-1 and K-3) recovered from patients who had failed ketoconazole therapy were 32- to 64-fold more resistant than the median of each drug for other isolates. In animal studies, fluconazole was very effective in prolonging survival of rats infected with a representative candidal strain. With an inoculum sufficient to kill 29 of 38 sham-treated animals, only 1 of 18 animals treated with 0.5 mg of fluconazole per kg per day died compared with 13 of 20 animals treated with 10.0 mg of ketoconazole per kg per day. However, when similar fluconazole treatment was administered to rats infected with the more resistant strain, K-1, no prolongation of survival was found. Thus, in vivo and in vitro results between strains correlated well for fluconazole. However, in comparing results between drugs, ketoconazole was 16-fold more active in vitro and fluconazole was 20-fold more active in vivo. This discrepancy may be due to drug distribution, modes of drug metabolism, or other pharmacologic differences between the two agents.

Estimations of serum arabinitol for diagnosing invasive candidosis

Arabinitol concentrations were determined in 157 serum samples from 95 patients with suspected invasive candidosis and in 10 serum samples from healthy laboratory workers. Fifty eight of the 95 patients, subsequently diagnosed as not having invasive candidosis had concentrations of arabinitol below 1.2 micrograms/ml (mean 0.59 (SD) 0.26). Sera from the healthy laboratory workers gave similar results (mean 0.55 (0.05]. Concentrations above the normal range were found in 18 of the 19 cases of confirmed or probable invasive candidosis and in seven of eight patients with infected intravenous lines or cannulas and clinical evidence of systemic infection. Raised concentrations were also seen in 10 other patients, including nine with renal failure who did not have invasive infections. Multiple serum samples obtained from 33 patients showed that sequential estimations were of value for diagnosing a developing infection. Despite some difficulties of interpretation the technique is rapid and specific and is suitable for use in the diagnostic laboratory of a larger general hospital.

New developments in the diagnosis of opportunistic fungal infection

This review considers recent developments in the diagnosis of aspergillosis, candidosis and cryptococcosis and discusses the prospects for routine application of a number of novel methods. The introduction of lysis-centrifugation and radiometric methods for blood culture has improved the diagnosis of deep candidosis, but the value of these methods for the diagnosis of aspergillosis has not yet been determined. Recent developments in serological diagnosis have included the evaluation of newly discovered antigens of Candida albicans in an attempt to distinguish colonization from significant infection. Antigen detection, an established method for the diagnosis of cryptococcosis, has also been evaluated and appears promising for the diagnosis of aspergillosis and candidosis. Another promising approach has been the use of gas-liquid chromatography to detect fungal metabolites in serum and other host fluids.

Value of serum arabinitol for the management of Candida infections in clinical practice

To determine the value of serum arabinitol concentrations in clinical practice, we identified all patients at the University of Utah Medical Center for whom a serum arabinitol determination had been requested by the attending physician or housestaff to assist in the management of candidiasis. The patient population was divided into three categories on the basis of clinical and pathological findings: superficial candidiasis, possible deep, invasive candidiasis, and definite, deep invasive candidiasis. Abnormal renal function was associated with elevated concentrations of serum arabinitol in proportion to the degree of renal dysfunction. Both the serum arabinitol concentration and the arabinitol/creatinine ratio were increased in the combined patient population with candidiasis relative to normal uninfected controls (p = 0.06 and 0.001, respectively). However, neither of these tests reliably distinguished patients with invasive candidiasis from those with only superficial candidal disease.

Enzymatic fluorometric method for the determination of D-arabinitol in serum by initial rate analysis

We describe a new, simple, fluorometric assay for D-arabinitol in serum. The method is based on oxidation of D-arabinitol by D-arabinitol dehydrogenase (EC 1.1.1.11), with the concomitant reduction of NAD. The initial rate of NAD reduction, which is proportional to the D-arabinitol content of serum, can be measured with a recording spectrofluorometer. Sensitivity, specificity, recovery and reproducibility experiments gave satisfactory results. The proposed method is suitable for clinical use, and may be helpful in the diagnosis of invasive candidiasis.

Comparison of enzyme immunoassay and gas-liquid chromatography for the rapid diagnosis of invasive candidiasis in cancer patients

Three proposed quantitative markers for candidiasis, arabinitol, mannose, and mannan in serum, are compared in 50 normal blood donors and 38 high-risk patients, 23 with and 15 without invasive candidiasis. Arabinitol concentrations in serum, the arabinitol/creatinine ratio, and mannose concentrations in serum were significantly greater in the 15 patients without candidiasis than in the normal blood donors (P less than 0.05). The sensitivities and specificities were 26 and 87% for arabinitol, 13 and 93% for the arabinitol/creatinine ratio, and 39 and 87% for mannose. On the other hand, mannan concentrations in serum were less than 1 ng/ml in normal blood donors and patients without candidiasis (P = 0.344), and the sensitivity and specificity were 65 and 100%, respectively. Of 23 patients with proven or probable candidiasis, 16 had mannan levels in serum greater than the mean + 2 standard deviations (0.46 ng/ml) for the 15 controls. In 16 patients with invasive candidiasis and positive blood cultures for the Candida spp., only 13 had elevated levels of at least one of the three markers. The arabinitol/creatinine ratio, the mannose level, and the mannan level became elevated an average of 4 days before, 1 day before, and on the same day that the blood cultures were drawn, respectively. Conversely, mannan was detected in the sera of six of seven patients with invasive candidiasis and negative blood cultures. We conclude that the best approach to diagnosing invasive candidiasis involves obtaining blood cultures and carrying out serial assays for mannan in serum.

Ornithyl amphotericin methyl ester treatment of experimental candidiasis in rats

After intravenous Candida albicans infection, rats received orinthyl amphotericin methyl ester, amphotericin B, or diluent intravenously. At doses of 0.1 and 0.5 mg/kg, the drugs were equally effective in preventing deaths. However, at doses of 2.0 mg/kg, mortality after treatment with amphotericin B was greater than that after placebo, whereas orinthyl amphotericin methyl ester was fully protective.

Clinical correlations of serial quantitative blood cultures determined by lysis-centrifugation in patients with persistent septicemia

The potential clinical value of colony counts determined by the lysis-centrifugation blood culture method was studied by reviewing the records of eight patients with persistent septicemia in whom colony counts were available on at least 3 days. Colony counts of the five patients who survived decreased steadily as the patients improved. One of the three patients who died had counts repeatedly below 1.0 CFU/ml while she was clinically stable and higher counts when her condition deteriorated. Two patients died despite decreasing colony counts. One was improving and died unexpectedly of an unrelated cause; the other died of candidiasis, but declining serial arabinitol/creatinine ratios suggested a partial response to therapy. In addition, septicemia related to infected intravenous catheters was documented by demonstrating large differences in colony counts determined simultaneously from two different sites in two patients and by demonstrating a precipitous drop in CFU per milliliter after removal of the infected catheter in one patient. Routine availability of colony counts appears to be an important advantage of the lysis-centrifugation method.

Comparison of serum mannan, arabinitol, and mannose in experimental disseminated candidiasis

Concentrations of arabinitol, mannose, and mannan in serum have independently been reported to be elevated in patients with invasive candidiasis. These three marker substances were compared in a rabbit model. Twelve rabbits, immunosuppressed with cortisone, were infected intravenously with Candida albicans 3181A. Six uninfected control animals also received cortisone, and four rabbits were neither infected nor immunosuppressed. Blood samples, drawn from 2 days before to 14 days after infection, were assayed for serum mannan by sandwich enzyme immunoassay, antibodies to mannan by indirect enzyme immunoassay, arabinitol and mannose by gas-liquid chromatography, and serum creatinine. Serum mannan, negative before infection, peaked in all infected animals 4 days after infection (mean, 18 ng/ml) and decreased thereafter. Significant increases (2 standard deviations greater than mean in normals) in arabinitol, the arabinitol/creatinine ratio, and mannose were found in 12, 8, and 12 of the infected rabbits, respectively, but also in all 6 uninfected animals receiving cortisone. Only serum mannan was specific in this immunosuppressed rabbit model.

Opportunistic fungal infections in patients with neoplastic disease

Opportunistic infections with yeast and molds are increasingly common in patients with neoplastic diseases. Candida species, Aspergillus species, Phycomyces, and Cryptococcus neoformans remain most common, but other organisms are being encountered as pathogens. With the exception of Cryptococcus, most opportunistic fungal infections are difficult to diagnose. New diagnostic tests for these diseases are being evaluated. Amphotericin B remains the antifungal agent of choice. In certain patients, the addition of 5-fluorocytosine may improve the outcome. Experience with cryptococcosis in severely immunocompromised cancer patients at Memorial Sloan-Kettering Cancer Center suggests that those who are treated with amphotericin B intravenously and intraventricularly via an Ommaya reservoir along with 5-fluorocytosine do better than those treated with amphotericin B alone.

Evaluation of serum arabinitol as a diagnostic test for candidiasis

Gas-liquid chromatography was used to quantitate the arabinitol concentration in the sera of patients with candidiasis and in that of control patients. Serum arabinitol was elevated in 59% (n = 34) of patients with Candida sepsis, in 39% (n = 38) with Candida colonization, in 14% (n = 62) with bacterial sepsis, and in 0% (n = 11) of normal persons. The above patients were subsequently divided on the basis of renal function. Of those with decreased renal function, serum arabinitol was elevated in 89, 92, and 50% of patients with Candida sepsis, Candida colonization, and bacterial sepsis, respectively. Of those with normal renal function, serum arabinitol was elevated in only 23 and 14% of patients with Candida sepsis and Candida colonization, respectively. When serum arabinitol/creatine ratios were calculated for patients with both increased arabinitol and increased creatinine, elevated ratios were obtained in 69, 36, and 0% of patients with Candida sepsis, Candida colonization, and bacterial sepsis, respectively.

Simultaneous determination of arabinitol and mannose by gas-liquid chromatography in experimental candidiasis

A method is described for the simultaneous quantitation of D-arabinitol and D-mannose in serum by gas-liquid chromatography as an aid for the diagnosis of disseminated candidiasis. Both variables were observed as per-O-acetylated aldononitrile derivatives in each chromatographic run of sera from immunosuppressed rabbits experimentally infected with Candida albicans 3181A.