Computer-assisted rapid enzyme-linked immunosorbent assay (ELISA) in the serological diagnosis of aspergillosis

A comparison of methods for the detection of Candida antigens. Evaluation of a new latex reagent

The sensitivity of various serological techniques for the detection of C. albicans cytoplasmic antigen (Ag) in buffer and serum diluents was compared, with special reference to variations of the ELISA method and a new microtitre latex particle agglutination (MLA) test. Of the assays evaluated, immunodiffusion, counterimmunoelectrophoresis and slide latex particle agglutination (SLA) were the least sensitive. ELISA tests were more sensitive (50-150 ng/ml Ag in buffer) although sensitivity decreased in serum or heat-inactivated serum (HIS) (250 ng/ml-4 micrograms/ml). The new MLA test had better sensitivity (16 ng/ml Ag in buffer) than any of the ELISA tests and was unaffected by the presence of serum or HIS (2.5 and 20 ng/ml Ag respectively). MLA seems worthy of further evaluation as an alternative to ELISA for use in antigen detection systems in general and for the serodiagnosis of systemic candidosis in particular.

[Application of micro-ELISA in serodiagnosis of fascioliasis in cattle]

Fascioliasis in cattle is one of the most common and very serious trematode diseases in Korea. In the present study, the enzyme linked immunosorbent assay (ELISA) was applied in the diagnosis of fascioliasis using antigen of Fasciola hepatica, peroxidase of conjugate anti-cattle IgG and orthophenylenediamine as a substrate by micro-method technique of Voller et al. (1976b) and MacLaren (1978) with a slight modification. Results obtained from the present study are as follows: In assay for optimal dilution of stock antigen, the antigen (protein contents; 0.8 mg/ml) was diluted from 1/50 to 1/600 with carbonate buffer (pH 9.6), and then absorbance values were measured with 1/100 diluted sera. The regression equations between the OD values of ELISA and dilution of antigen were log Y=-0.181-0.00127X in infected sera, and log Y= -0.578- 0.000879X in normal sera. The significantly higher (p<0.05) OD value was observed in the former. In assay for optimal dilution of sera, the sera were diluted from 1/25 to 1/400 with in PBS/ Tween 20(pH 7.4), and absorbance values were measured with 1/200 diluted antigen. The regression equation between the OD values of ELISA and dilution of sera were log Y=-0.1540-0.0007238X in infected sera and log Y=-0.4834-0.00116X in normal sera. The former was higher than the latter (p<0.05). In the 27 cases of negative intradermal test, OD values of the ELISA are 0.447 +/- 0.144, the 95 percent confidence interval (Mean + 2 x SD) of the values was 0.735, and there was no case over the values. Therefore, the sensitivity of the antigen to diagnose fascioliasis was 100 percent in the negative case. The OD value 0.7 which is designed as a criterion (detection level of positive one) is useful for the performance of the ELISA in fascioliasis. According to the OD value of criterion in the regression equations, the optimal dilutions of stock antigen and serum were 1/250 and 1/100, respectively. In the 58 cases of fascioliasis from which the adult could be found in the bile ducts, the OD value was 0.846 +/- 0.224). The 75 percent (44 cattle) among them had higher value with compared to the criterion, and the 60 percent (20 cattle) of the cases of proliferative cholangitis of 33 cattle which had been infected previousely with Fasciola sp. is higher than the criterion. Prevalence of fascioliasis was 43.4 percent in the application of the ELISA to 272 cattle which were reared in Jeonbug district.

A computer program for the evaluation of ELISA data obtained using an automated microtiter plate absorbance reader

A new computer program is described which calculates titers and antibody concentrations from ELISA data. Optical densities are measured in 96-well microtiter plates using an automated colorimeter and simultaneously fed into a microcomputer. The data can then be arranged and printed in an 8 X 12 format corresponding to the format of a 96-well microtiter plate. The computer program can also compute the titers of samples if the samples are arranged and titrated in one of the suggested formats. In addition, the titers of unknown samples can be automatically compared with the titer of a standard to obtain concentrations. An ELISA designed to measure the concentration of murine antibodies to the cell wall polysaccharide (PnC) extracted from Streptococcus pneumoniae was performed to document the use of the program.

Antibody to Aspergillus fumigatus antigens in normal sera: influence on positive-negative discrimination in ELISA

The response of precipitin-negative sera from non-selected asthmatic patients against a range of somatic and culture filtrate antigens of Aspergillus fumigatus in ELISA for anti-A. fumigatus IgG is described. Antibody to the various antigens was widely distributed but the precise distribution was dependent upon antigen type. To determine how the selection of negative reference sera from precipitin-negative sera can influence the discrimination between precipitin-positive and -negative sera in ELISA, panels of 10 sera were chosen from the extremes of the frequency distribution and by random selection. The closest agreement between precipitin testing and ELISA was seen when randomly-selected negative reference sera were incorporated in the assay, although the degree of correlation was dependent upon the detector antigen. These findings demonstrate the requirement for careful selection of sera included as negative reference sera in ELISA for anti-A. fumigatus IgG.

Computer-assisted multiple categorization of absorbance values in ELISA through pictorial emulation of 96-well plates

A simple algorithm is proposed by which multiple categorization of absorbance values from ELISA plates is performed under a microcomputer control. The printed output is a pictorial emulation of a 96-well plate with the color intensities represented for each reaction. Although the method is presented as a colorimeter computer interfaced system, a provision for manual entry of absorbance values via keyboard is also included. Simulation is based solely on the magnitude of absorbance values. Therefore, it is possible to utilize any enzyme/substrate combination within the range of filters of the colorimeter. We have tested the present system for titration of anti-malarial antibodies in human serum and for the screening of mouse hybridoma culture supernatants.

Antigen and antibody attachment in ELISA for Aspergillus fumigatus IgG antibodies

Four commercial antigen extracts of Aspergillus fumigatus were evaluated for use in a rapid enzyme-linked immunosorbent assay (ELISA) for anti-A. fumigatus IgG. Initial binding of both somatic and culture filtrate preparations to a polyvinyl chloride solid phase was concentration dependent and increased with incubation time. Antigen binding to the solid phase was reproducible. Binding of A. fumigatus precipitin-positive serum to bound antigen was rapid. All four A. fumigatus antigens demonstrated similar dose-response curves when tested against pooled sera containing a high titre of A. fumigatus antibodies. Detectable activity in precipitin test-negative sera decreased rapidly with dilution. All the antigen preparations were found to be suitable for ELISA procedures and permit the rapid determination of IgG antibodies to A. fumigatus.

Evaluation of an enzyme-linked immunosorbent assay (ELISA) for the diagnosis of Aspergillus fumigatus intranasal infection of the dog

ELISA appears to be a less reliable method than counterimmunoelectrophoresis for the diagnosis of nasal aspergillosis in the dog. False-positive or false-negative results were recorded for anti-A. fumigatus IgG in nine animals with aspergillosis and in 27 disease-free dogs although this problem could be reduced with careful selection of antigen.

A computer-based data analysis system for enzyme-linked immunosorbent assays

A computerized system is presented for automating the data collection, processing, and displaying tasks involved in enzyme-linked immunosorbent assays. This system uses a through-the-well absorbance reader of microtiter plates interfaced to a minicomputer running the UNIX operating system. Optical density in each well of a 96-well microtiter plate is recorded as a function of time for up to 10 time points. These data are automatically transmitted to the remote computer. The rate of product formation is then calculated for each well, and a battery of analysis, display, and comparison programs can then be used by the researcher for data presentation. Using the initial rate of reaction as the basis for quantifying enzyme-linked immunosorbent assays focuses on the catalytic property of the enzyme and allows a large dynamic range of the assay on any plate. These programs can be adapted to virtually any mini- or microcomputer with a graphics display or a plotting device. Assuming moderately powerful computing hardware, throughputs of 50 plates per day are easily achieved. The programs work equally well with peroxidase, beta-galactosidase, or alkaline phosphatase conjugated second antibodies, and with whole cell or soluble antigens.

Computer-assisted determination of antibiotic susceptibility in photometer-read microtiter plates

A method for the computer-assisted determination of microdilution minimal inhibitory concentrations by using a Dynatech MR580 through-the-plate reading photometer is presented. The method was evaluated by comparison with manual determination of the minimal inhibitory concentrations of 12 antibiotics for 115 bacterial isolates. The two methods agreed within one dilution in 98.3% of the cases.

Comparison of partially purified mycelial and culture filtrate antigens of Aspergillus fumigatus by enzyme-linked immunosorbent assay

An aqueous extract of Aspergillus fumigatus mycelium was fractionated by precipitation with ammonium sulphate to give protein-enriched and carbohydrate-enriched preparations. The antigenic activity of the fractions so obtained was assessed in an enzyme-linked immunosorbent assay using pooled positive and negative reference sera. The best discrimination between such sera was obtained when using either the fraction insoluble in 50--75% ammonium sulphate or the material soluble in a saturate solution of the salt. This system was then used in parallel with commercial A. fumigatus extracts to test sera of patients with and without clinical aspergillosis. The implications of the results are discussed.