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

Silver nanoparticles (AgNPs) based selective colorimetric sensor for the detection of D-arabinitol in a urine sample

D-arabinitol is a sugar alcohol that is a typical metabolite of Candida species. The hydroxy group owned by D-arabinitol can function as a reducing agent that can reduce Ag+ to AgNPs. The resulting colloid is further stabilized by the addition of a capping agent. The capping agent used in this study was a combination of chitosan 1%(w/w) and PEG 6000 1% (w/w) (2:1) v/v. The formation of AgNPs causes an increase in the surface plasmon resonance spectra of the colloid solution at a wavelength of 430 nm with a slight blue shift. At the same time, the color of the solution changes from colorless to yellow colloid so that the absorbance can be observed using a spectrophotometer. The change in the absorbance value of the colloid produced is proportional to the concentration of D-arabinitol added, so that the amount of D-arabinitol in the sample can be quantified. Under optimum conditions, the resulting method shows good linearity with an R2-value of 0.9979 in the concentration range of D-arabinitol 100-2000 μM and Vxo value is 4.30%. The detection limit is 115.11 μM and the quantification limit is 383.70 μM. The repeatability (%RSD) is 0.78-1.94 and the % recovery in addition to urine samples is 93.27-103.70. This method is quite selective for other components present in urine. The analysis time is short, the number of samples required is only small, and does not require an organic solvent, so this method has the potential to be used in determining the levels of D-arabinitol in urine samples.

A novel molecular imprinting polymer for the selective adsorption of D-arabinitol from spiked urine

In this research, molecular imprinting polymers (MIPs) for D-arabinitol were synthesized using a bulk polymerization method through a noncovalent approach. The MIPs were prepared by using D-arabinitol as a template, acrylamide as a functional monomer, ethylene glycol dimethacrylateas cross-linker, benzoyl peroxide as an initiator and dimethyl sulfoxideas a porogen. MIPS was synthesized in several formulas with a different molar ratio of template to functional monomers and cross-linker. Fourier-transform infrared spectroscopy (FT-IR) and scanning electron microscopy (SEM) were used to characterize the MIPs produced. A batch rebinding assay was used to test the binding efficiency of each formula. Batch rebinding test results revealed that MIPsF3 with a molar ratio of the template: monomer and crosslinker ratio respectively (1: 4: 25) had the highest binding capacity at 1.56 mgg ^-1 . The results of isotherm adsorption showed that the MIPs produced followed the Freundlich equation with an R-value of 0.97. The MIPs produced was also selective toward its isomeric compounds (i.e. L-arabinitol, adonitol, xylitol, and glucose). The extraction efficiency of the MIPs against D-arabinitol was 88.98%.

Serological response and diagnostic value of recombinant candida cell wall protein enolase, phosphoglycerate kinase, and β-glucosidase

There are no specific signs and symtoms for invasive candidiasis (IC), which makes its diagnosis a challenge. Efforts have been made for decades to establish serological assays for rapid diagnosis of IC, but none of them have found widespread clinical use. Using a systemic candiasis murine model, serological response to recombinant proteins of enolase (rEno1), phosphoglycerate kinase (rPgk1), and β-glucosidase (rBgl2) were evaluated and rEno1 was found to possess the strongest immunoreactivity, followed by rPgk1 and rBgl2. Likewise, IgG antibody titers to rEno1, rPgk1, and rBgl2 in the positive sera of proven IC patients were determined by ELISA. Results show anti-rEno1 antibody possesses the highest titer, followed by rPgk1 and rBgl2. Antibodies against rEno1, rPgk1, and rBgl2 were detected by ELISA tests in a group of 52 proven IC patients or 50 healthy subjects, The sensitivity, specificity, positive and negative predictive values were 88.5, 90.0, 90.2, and 88.2% for anti-rEno1 detection, 86.5, 92.0, 91.8, and 86.8% for anti-rPgk1 detection, and 80.8, 90.0, 89.4, and 81.8% for anti-rBgl2 detection, respectively. The data clearly demonstrate that the recombinant proteins of Eno1, Pgk1, and Bgl2 are promising candidates for IC serodiagnosis. There's great possibility that the recombinant Eno1 will be more applicable in serodiagnosis and vaccine research on account of its strong serological response.

Biochemical characterization of the CDP-D-arabinitol biosynthetic pathway in Streptococcus pneumoniae 17F

Streptococcus pneumoniae is a major human pathogen associated with many diseases worldwide. Capsular polysaccharides (CPSs) are the major virulence factor. The biosynthetic pathway of D-arabinitol, which is present in the CPSs of several S. pneumoniae serotypes, has never been identified. In this study, the genes abpA (previously known as abp1) and abpB (previously known as abp2), which have previously been reported to be responsible for nucleoside diphosphate (NDP)-D-arabinitol (the nucleotide-activated form of D-arabinitol) synthesis, were cloned. The enzyme products were overexpressed, purified, and analyzed for their respective activities. Novel products produced by AbpA- and AbpB-catalyzing reactions were detected by capillary electrophoresis, and the structures of the products were elucidated using electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. As a result, abpA was identified to be a D-xylulose-5-phosphate cytidylyltransferase-encoding gene, responsible for the transfer of CTP to D-xylulose-5-phosphate (D-Xlu-5-P) to form CDP-D-xylulose, and abpB was characterized to be a CDP-D-xylulose reductase-encoding gene, responsible for the conversion of CDP-D-xylulose to CDP-D-arabinitol as the final product. The kinetic parameters of AbpA for the substrates D-Xlu-5-P and CTP and those of AbpB for the substrate CDP-D-xylulose and the cofactors NADH or NADPH were measured, and the effects of temperature, pH, and cations on the two enzymes were analyzed. This study confirmed the involvement of the genes abpA and abpB and their products in the biosynthetic pathway of CDP-D-arabinitol.

Invasive mycoses: diagnostic challenges

Despite the availability of newer antifungal drugs, outcomes for patients with invasive fungal infections (IFIs) continue to be poor, in large part due to delayed diagnosis and initiation of appropriate antifungal therapy. Standard histopathologic diagnostic techniques are often untenable in at-risk patients, and culture-based diagnostics typically are too insensitive or nonspecific, or provide results after too long a delay for optimal IFI management. Newer surrogate markers of IFIs with improved sensitivity and specificity are needed to enable earlier diagnosis and, ideally, to provide prognostic information and/or permit therapeutic monitoring. Surrogate assays should also be accessible and easy to implement in the hospital. Several nonculture-based assays of newer surrogates are making their way into the medical setting or are currently under investigation. These new or up-and-coming surrogates include antigens/antibodies (mannan and antimannan antibodies) or fungal metabolites (d-arabinitol) for detection of invasive candidiasis, the Aspergillus cell wall component galactomannan used to detect invasive aspergillosis, or the fungal cell wall component and panfungal marker β-glucan. In addition, progress continues with use of polymerase chain reaction- or other nucleic acid- or molecular-based assays for diagnosis of either specific or generic IFIs, although the various methods must be better standardized before any of these approaches can be more fully implemented into the medical setting. Investigators are also beginning to explore the possibility of combining newer surrogate markers with each other or with more standard diagnostic approaches to improve sensitivity, specificity, and capacity for earlier diagnosis, at a time when fungal burden is still relatively low and more responsive to antifungal therapy.

Comparative evaluation of (1, 3)-beta-D-glucan, mannan and anti-mannan antibodies, and Candida species-specific snPCR in patients with candidemia

BACKGROUND

Candidemia is a major infectious complication of seriously immunocompromised patients. In the absence of specific signs and symptoms, there is a need to evolve an appropriate diagnostic approach. A number of methods based on the detection of Candida mannan, nucleic acid and (1,3)-beta- D- glucan (BDG) have been used with varying specificities and sensitivities. In this retrospective study, attention has been focused to evaluate the usefulness of two or more disease markers in the diagnosis of candidemia.

METHODS

Diagnostic usefulness of Platelia Candida Ag for the detection of mannan, Platelia Candida Ab for the detection of anti-mannan antibodies, Fungitell for the detection of BDG, and of a semi-nested PCR (snPCR) for the detection Candida species-specific DNA have been retrospectively evaluated using 32 sera from 27 patients with culture-proven candidemia, 51 sera from 39 patients with clinically suspected candidemia, sera of 10 women with C. albicans vaginitis, and sera of 16 healthy controls.

RESULTS

Using cut-off values recommended by the manufacturers, the sensitivity of the assays for candidemia patients were as follows: Candida snPCR 88%, BDG 47%, mannan 41%, anti-mannan antibodies 47%, respectively. snPCR detected 5 patients who had candidemia due to more than one Candida species. The sensitivities of the combined tests were as follows: Candida mannan and anti-mannan antibodies 75%, and Candida mannan and BDG 56%. Addition of snPCR data improved the sensitivity further to 88%, thus adding 10 sera that were negative by BDG and/or mannan. In clinically suspected, blood culture negative patients; the positivities of the tests were as follows: Candida DNA was positive in 53%, BDG in 29%, mannan in 16%, and anti-mannan antibodies in 29%. The combined detection of mannan and BDG, and mannan, BDG and Candida DNA enhanced the positivity to 36% and 54%, respectively. None of the sera from Candida vaginitis patients and healthy subjects were positive for Candida DNA and mannan.

CONCLUSION

The observations made in this study reinforce the diagnostic value of snPCR in the sensitive and specific diagnosis of candidemia and detection of more than one Candida species in a given patient. Additionally, in the absence of a positive blood culture, snPCR detected Candida DNA in sera of more than half of the clinically suspected patients. While detection of BDG, mannan and anti-mannan antibodies singly or in combination could help enhancing sensitivity and eliminating false positive tests, a more extensive evaluation of these assays in sequentially collected serum samples is required to assess their value in the early diagnosis of candidemia.

Clinical experience of urine D-arabinitol/L-arabinitol ratio in the early diagnosis of invasive candidiasis in paediatric high risk populations

In 2 prospective studies, we previously reported on the early and accurate diagnosis of invasive candidiasis by determining the D-arabinitol/L-arabinitol (DA/LA) ratio in urine in neutropenic children with cancer at the paediatric oncology unit (POU) and in premature infants at the neonatal intensive care unit (NICU) at our hospital. In this retrospective study at the same units, we report how the DA/LA assay was implemented in clinical practice immediately after the prospective study periods. We found that, in the POU, the recommendation of regularly monitoring urine DA/LA ratios in patients at risk and considering antifungal therapy in the case of elevated ratios had been followed. A significant decrease in the incidence of culture positive invasive candidiasis may have been attributed to the introduction of the DA/LA assay. At the NICU, where the DA/LA assay was recommended only as an adjunct to other diagnostic tools, morbidity in invasive candidiasis remained unchanged. While regular monitoring of the urine DA/LA ratio probably facilitates the early detection of invasive candidiasis in paediatric oncology, it remains to be determined if the test can be used in a similar way in neonatal intensive care.

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.

Development and application of a rapid diagnostic method for invasive Candidiasis by the detection of d-/l-arabinitol using gas chromatography/mass spectrometry

A rapid non-culture-based diagnostic method utilizing d-/l-arabinitol (DA/LA) ratios as a chemical marker of invasive candidiasis was developed and explored. The enantiomers-ratios detection was made possible by the use of gas chromatography coupled with mass spectrometry (GC/MS). The mean DA/LA ratios +/- standard deviation (range) in urine (n = 40) and serum (n = 20) were 2.08 +/- 0.78 (0.57 to 3.55) and 1.79 +/- 0.75 (0.74 to 3.54), respectively, from patients without evidence of fungal infection or colonization; in patients (n = 7) with culture-proven invasive candida infections, the figures were 9.91 +/- 3.04 (7.24 to 16.27) and 13.58 +/- 7.31 (5.57 to 25.88) in urine and serum, respectively. The differences in DA/LA ratios between the candidemic patients and the non-candidemic patients were statistically significant (p < 0.01) in both serum and urine samples. The DA/LA ratios were not significantly affected in patients with oral or vaginal candidiasis and candiduria.

Increased sensitivity of mannanemia detection tests by joint detection of alpha- and beta-linked oligomannosides during experimental and human systemic candidiasis

An enzyme immunoassay (EIA)-the commercially available Platelia Candida antigen test-developed for the diagnosis of systemic candidiasis is based on the detection of alpha-linked oligomannose residues (alpha-Man) released from Candida cells into the serum. This test has good specificity but has to be repeated frequently because of the rapid clearance of detectable mannanemia. We have developed a second EIA based on detection of beta-linked oligomannoses (beta-Man), since beta-Man are linked to different Candida molecules and interact differently with the host immune system and endogenous lectins and should therefore present different kinetics of serum clearance. In a guinea pig model of Candida albicans systemic infection, the relative amounts of detectable alpha- and beta-Man differed considerably according to the virulence of the strain, the infecting dose, and the time after challenge that serum samples were drawn. Detection of alpha-Man was more sensitive per serum sample than that of beta-Man, and the sensitivity for the combination reached 90%. The same tests were applied to 90 sera from 26 patients selected retrospectively for having been infected with the most-pathogenic Candida species: C. albicans (19), C. tropicalis (4), and C. glabrata (3). A total of 22 patients had positive antigenemia, 4 had alpha-mannanemia, 4 had beta-mannanemia, and 14 showed the presence of both. For the patients showing the presence of both forms of mannanemia, the use of both tests enhanced the duration of the detection of mannanemia. Mannanemia was correlated with early clinical symptoms and isolation of Candida in culture, which occurred in 55% of the patients at an average of 4.7 days after the first positive mannanemia test result. A combination of the two tests had a cumulated specificity of 95%, and positive and negative predictive values were 79 and 97%, respectively. These findings provide evidence for different kinetics of beta- and alpha-Man circulation during experimental and human candidiasis and suggest the joint detection of both types of epitopes as a rational approach contributing to increases in the sensitivity and earliness of diagnosis.

Pseudomonas fluorescens mannitol 2-dehydrogenase and the family of polyol-specific long-chain dehydrogenases/reductases: sequence-based classification and analysis of structure-function relationships

Multiple sequence alignment and analysis of evolutionary relationships have been used to characterize a family of polyol-specific long-chain dehydrogenases/reductases (PSLDRs). At the present time, 66 known and putative NAD(P)H-dependent oxidoreductases of mainly prokaryotic origin and between 357 and 544 amino acids in length constitute this family. The family is shown to include D-mannitol 2-dehydrogenase, D-mannonate 5-oxidoreductase, D-altronate 5-oxidoreductase, D-arabinitol 4-dehydrogenase, and D-mannitol-1-phosphate 5-dehydrogenase which form individual sub-families (defined by internal sequence identity of >/=30%) having distant origin and divergent substrate specificity but clearly displaying entire-chain relationship. When all forms are aligned, only three residues, Gly-33, Asp-230, and Lys-295 (in the numbering of Pseudomonas fluorescens D-mannitol 2-dehydrogenase (PsM2DH)) are strictly conserved. By combining sequence alignment with the known structure of PsM2DH and results from site-directed mutagenesis, we have developed a structure/function analysis for the family. Gly-33 is in the N-terminal coenzyme-binding domain and part of a nucleotide fingerprint region for the family, and Asp-230 and Lys-295 are at an interdomain segment contributing to the active site in which the lysine likely functions as the catalytic general acid/base. PSLDRs do not require a metal cofactor for activity and are specific for transferring the 4-pro-S hydrogen from NAD(P)H. Comparisons reveal that the core part of the two-domain fold has been conserved throughout all family members, perhaps reflecting the recruitment of a stable oxidoreductase structure and extensive trimming thereof to acquire functional properties specific to each sub-family. They also identify interactions that define the chemical mechanism of oxidoreduction and likely contribute to substrate and co-substrate specificities and are thus relevant for protein engineering.

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.

Diagnosis of systemic Candida infections in patients of the intensive care unit. Significance of serum antigens and antibodies

The combined detection of Candida antigen and antibody for the determination of systemic Candida infections (SCI) was investigated. One hundred and four patients from the intensive care unit (ICU) were analysed. Seventeen of the patients were suspected of having SCI, based on clinical and laboratory criteria. In these patients, Candida antigens and antibodies were analysed extensively. Ten patients had a positive Candida antigen (titre >1:16) determined by the latex agglutination assay Cand-Tec(R) and their median antibody titre was 1:160 in the indirect haemagglutination test (HAT). Seven antigen-negative patients had a median titre of 1:1280 (HAT). Forty-one of 42 colonized control patients had negative antigen titres and a median antibody titre of 1:160. The sensitivities and specificities were 58.8% and 97.6% for antigenemia, and 52.9% and 85.7% for antibody detection. These values reached 100.0% and 83.3%, respectively, when the results of both tests were combined. This indicates a high degree of concordance between serological results (Candida antigen and/or antibodies) and clinical presentation. We conclude, that the combined investigation of antigen and antibody titres might be a helpful tool in the characterization of SCI in ICU patients, if antigen titres are >or=1:16 or antibody titres (HAT) are >or=1:640.