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Biomedical subjects

S Nesheim

Publications and source records attributed to S Nesheim.

At least 37 records · Page 2Linked to original sources
PubMed1989

ELISPOT: a new approach to studying the dynamics of virus-immune system interaction for diagnosis and monitoring of HIV infection.

A new approach to detect and enumerate HIV-specific antibody-secreting cells (ASC) in the peripheral blood was developed using the enzyme-linked immunospot (ELISPOT) methodology. ASC to an HIV envelope recombinant protein were demonstrated in 75% of 16 adults and 72% of 21 children with untreated AIDS or ARC and in 63% of 34 asymptomatically infected adults but in none of the 51 HIV antibody-negative individuals. Only 1 of the 13 adults receiving AZT therapy yielded a positive reaction, and 27% of the 30 infants born to seropositive mothers were found to have HIV-ASC. The number of HIV-ASC in positive individuals varied from 8 to 202 per 10(6) circulating mononuclear cells. The reactivity was specifically inhibited by soluble HIV antigen and was abrogated by cycloheximide, indicating that the observed reaction was the result of de novo synthesis of HIV-specific antibodies. Nonspecific polyclonal B cell activation was unlikely to be responsible for the results observed as no reactivity was found to a common antigen, tetanus toxoid. Since circulating antigen-specific ASC reflect persistent or recent antigenic stimulation, our findings indicate that this new approach could provide a dynamic perspective of the natural course of virus-immune system interactions in individuals infected with HIV, as well as in those undergoing prophylactic or therapeutic interventions.

AIDS-Related Complex↗
PubMed1981

Minicolumn detection methods for aflatoxin in raw peanuts: collaborative study.

The Holaday-Velasco method and a modified Holaday method have been compared. The former method combines the speed and simplicity of the Holaday extraction and cleanup with the sensitivity of the minicolumn originally described by Velasco. The combination method has been approved by the AOAC and the AACC for determining aflatoxin in corn. The Holaday method was modified by substituting toluene for benzene in the solvent partition, and methylene chloride for chloroform in the minicolumn development to eliminate use of hazardous solvents. The neutral alumina in the Holaday minicolumn was changed from activity V to activity III to provide a more stable column. At aflatoxin levels in raw peanuts of 13-20 ng/g, the presence of aflatoxin was missed by the modified Holaday method in 4 analyses (3 laboratories) of 42 reported. There were no misses in this contamination range by the Holaday-Velasco method. There were no misses by either method with samples containing greater than 20 ng total aflatoxins/g. Analysis of uncontaminated raw peanuts by the modified Holaday method resulted in 2 false positives of 14 reports; the Holaday-Velasco method produced no false positive reports from 15 analyses of uncontaminated peanuts. The Holaday-Velasco method was adopted official first action for peanuts.

Aflatoxins↗
PubMed1978

Thin layer chromatographic determination of aflatoxin B1 in eggs: collaborative study.

The thin layer chromatographic method of Trucksess et al. for aflatoxin B1 in eggs was collaboratively studied. Each collaborator analyzed 3 known practice samples and 9 unknown samples containing added aflatoxin B1 at 0, 0.05, 0.10, and 0.30 ng/g. For 9 collaborators, recoveries for the 3 positive levels were: 0--0.13 ng/g (average 98%, coefficient of variation (C.V.) 83%), 0.05--0.18 ng/g (average 102%, C.V. 36%, and 0.11--0.42 ng/g (average 93%, C.V. 31%), respectively. The method has been adopted as official first action.

Aflatoxins↗
PubMed1977

Aflatoxins in Egyptian foodstuffs.

Six samples each of wheat, corn, lentils, beans, fenugreek, peanuts, and cottonseed cake from various areas of Egypt were analyzed for aflatoxins both at the time of collection and after 12 months' storage. Aflatoxin was found at low levels (3 to 12 ppb total aflatoxins in 14 of 42 samples, as follows: 1 sample each of corn, lentils, and beans; 2 peanut samples; 3 fenugreek samples; and 6 cottonseed cake samples. None of the samples contained aflatoxins above 11.7 ppb.

Aflatoxins↗
PubMed1976

Determination of sterigmatocystin in corn and oats by gel permeation and high-pressure liquid chromatography.

Corn and oats samples are extracted with acetonitrile-water, followed by partition of the extract against hexane, transfer to chloroform, and elution from a silica gel column. The extract is purified by gel permeation chromatography on an automatic instrument. Reverse phase high-pressure liquid chromatography, using a 254 nm ultraviolet detector and 0.1 M KH2PO4-acetonitrile (7+5) as the mobile phase, is used for quantitation. The average recovery from 6 samples of corn to which 0, 25, 50, and 100 mug sterigmatocystin/kg had been added was 59%, with a coefficient of variation of 8.4%. The average recovery from oats fortified at the same levels was 74%, with a coefficient of variation of 12%. A confirmation procedure based on hemiacetal derivative formation on a thin layer chromatographic plate is also described.

Chromatography, Gel↗
PubMedDate not supplied

Molar absorptivities of aflatoxins B1, B2, G1, and G2 in acetonitrile, methanol, and toluene-acetonitrile (9 + 1) (modification of AOAC Official Method 971.22): collaborative study.

Four laboratories participated in a mini-collaborative study of AOAC Official Method 971.22, Standards for Aflatoxins, Thin-Layer Chromatographic Method, to extend the method to 3 replacement solvents for benzene for calibration of standard aflatoxin solutions. Triplicate test sample vials, each containing 25 micrograms of the respective aflatoxin for each of the 4 aflatoxins and for each of the solvents, were prepared and sent to each collaborator. The collaborators dissolved the aflatoxin in each vial in 2 mL solvent, measured the UV spectrum, and reported the absorptivity maxima near 350 nm. The concentrations of the aflatoxins in the test samples were determined by dissolving identical test samples in benzene-acetonitrile (98 + 2) and following the procedure described in AOAC Official Method 971.22. These concentrations were, in turn, used to determine the molar absorptivities in the other 3 solvents (see Table 1). AOAC Official Method 971.22 has been modified to extend its applicability to 3 replacement solvents for benzene for calibration of standard aflatoxin solutions.

Absorption↗
PubMedDate not supplied

Immunoaffinity column coupled with solution fluorometry or liquid chromatography postcolumn derivatization for determination of aflatoxins in corn, peanuts, and peanut butter: collaborative study.

An AOAC/IUPAC (International Union of Pure and Applied Chemistry) collaborative study was conducted to evaluate the effectiveness of an immunoaffinity column for the determination of aflatoxin. The test portion is extracted with methanol-water (7 + 3), filtered, diluted to less than 30% methanol with water, and applied to the affinity column. The column is washed with water and the concentrated aflatoxins are eluted with methanol. Total aflatoxins are determined by solution fluorometry with bromine (SFB), and individual toxins are determined by reverse-phase liquid chromatography with postcolumn derivatization with iodine (PCD). Corn naturally contaminated with aflatoxins, and peanuts, peanut butter, and corn containing added aflatoxins (B1:B2:G1:G2 = 7:1:3:1) were sent to 24 collaborators in the United States, France, Canada, and the Republic of South Africa. Twelve collaborators used the SFB method, 9 used the PCD method, and 3 used both SFB and PCD methods. Twenty collaborators completed the study (10 used the SFB method, 7 used the PCD method, and 3 used both SFB and PCD methods). Test portions were spiked at 10, 20, and 30 ng/g. For SFB analyses, recoveries of total aflatoxins were 123, 105, and 107%, respectively; the relative standard deviation for repeatability (RSDr) ranged from 11.75 to 16.57%, and the relative standard deviation for reproducibility (RSDR) ranged from 10.97 to 33.09%. For PCD analyses, recoveries were 81, 81, and 83%, respectively; the RSDr ranged from 5.20 to 17.22%, and the RSDR ranged from 4.68 to 50.77%. The RSDr for aflatoxins B1 and G1 for spiked test portions ranged from 5.45 to 23.55%, and the RSDR ranged from 4.21 to 57.28%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxins↗
PubMedDate not supplied

Liquid chromatographic method for determination of aflatoxins B1, B2, G1, and G2 in corn and peanut products: collaborative study.

A collaborative study of a liquid chromatographic method for the determination of aflatoxins B1, B2, G1, and G2 was conducted in laboratories located in the United States, Canada, South Africa, and Switzerland. Twenty-one artificially contaminated raw peanuts, peanut butter, and corn samples containing varying amounts of aflatoxins B1, B2, G1, and G2 were distributed to participating laboratories. The test portion was extracted with methanol-0.1N HCl (4 + 1), filtered, defatted with hexane, and then partitioned with methylene chloride. The concentrated extract was passed through a silica gel column. Aflatoxins B1 and G1 were derivatized with trifluoroacetic acid, and the individual aflatoxins were determined by reverse-phase liquid chromatography with fluorescence detection. Statistical analysis of the data was performed to determine or confirm outliers, and to compute repeatability and reproducibility of the method. For corn, relative standard deviations for repeatability (RSDr) for aflatoxin B1 ranged from 27.2 to 8.3% for contamination levels from 5 through 50 ng/g. For raw peanuts and peanut butter, RSDr values for aflatoxin B1 were 35.0 to 41.2% and 11.2 to 19.1%, respectively, for contamination levels from 5 through 25 ng/g. RSDr values for aflatoxins B2, G1, and G2 were similar. Relative standard deviations for reproducibility (RSDr) for aflatoxin B1 ranged from 15.8 to 38.4%, 24.4 to 33.4%, and 43.9 to 54.0% for corn, peanut butter, and raw peanuts, respectively. The method has been adopted official first action for the determination of aflatoxins B1, B2, G1, and G2 in peanut butter and corn at concentrations greater than or equal to 13 ng total aflatoxins/g.

Aflatoxin B1↗
PubMedDate not supplied

Mycotoxin methodology.

The development of methods with high specificity and low limits of determination, as well as screening methods that are convenient for detection and rough quantitation of mycotoxins, has proceeded at an accelerating rate over the past few years. Of particular interest has been the widespread application of high performance liquid chromatographic and immunoassay techniques in mycotoxin methodology. An overview of the latest developments in mycotoxin methodology is presented with emphasis on the need for attention to sampling and sample preparation, the basic principles supporting the analytical methodology, the need for techniques to confirm analyte identification, and the requirement for high-quality reference materials.

Aflatoxins↗
PubMedDate not supplied

Visual and semiquantitative spectrophotometric ELISA screening method for aflatoxin B1 in corn and peanut products: follow-up collaborative study.

A joint AOAC/IUPAC (International Union of Pure and Applied Chemistry) interlaboratory study of an enzyme-linked immunosorbent screening assay (ELISA) for aflatoxins was conducted in laboratories in Canada, France, Japan, The Netherlands, Switzerland, Tunisia, and the United States. Twelve raw and roasted peanut and corn portions containing various concentrations of natural aflatoxins and supplemented when appropriate with aflatoxin B1 were distributed to participating laboratories for testing. The assay is based on competition between an enzyme-conjugated aflatoxin B1 and (free) aflatoxins in the test sample for aflatoxin-specific antibodies coated onto interior surfaces of microtiter wells. After a wash step to remove all unbound aflatoxins, a substrate added to each well is catalyzed from a colorless to a blue solution by any bound enzyme-conjugated aflatoxin B1 present. The intensity of the color decreases as the amount of free aflatoxin B1 in the test portion increases. Final determination of aflatoxin concentrations can be made by either visual comparison with standard solutions or spectrophotometric comparisons (at 650 nm) to knowns. Overall correlation was good between ELISA and thin-layer chromatographic results for corn and roasted peanut products, with 93 and 98% correct responses for visual and instrumental determinations, respectively. For instrumental determinations of aflatoxin in corn and roasted peanuts in the less than or equal to 20 ng/g range, the relative standard deviations for repeatability (RSDr) were 14.9 and 41.4%, respectively, and the relative standard deviations for reproducibility (RSDR) were 45.7 and 43.5%, respectively. For instrumental determination of greater than 20 ng/g, the respective RSDr and RSDR values were 19.4 and 52.7% for corn and 23.3 and 23.3% for roasted peanuts.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗
PubMedDate not supplied

Enzyme-linked immunosorbent assay of aflatoxins B1, B2, and G1 in corn, cottonseed, peanuts, peanut butter, and poultry feed: collaborative study.

A direct competitive enzyme-linked immunosorbent assay (ELISA) screening method for aflatoxins at 20 ng/g was studied by 12 collaborators. Test samples of peanut butter were extracted by blending with methanol-water-hexane (55 + 45 + 100) and heating the test extracts on a steam bath; test samples of the other commodities were extracted by blending with methanol-water (80 + 20). All test extracts were filtered and the filtrates were diluted with buffer to a final methanol concentration of less than 30%. Each diluted filtrate was applied to a cup containing a filter with immobilized polyclonal antibodies specific to aflatoxins B1, B2, and G1. Aflatoxin B1-peroxidase conjugate was added, the cup was washed with water, and a mixture of hydrogen peroxide and tetramethylbenzidine was added. The test sample was judged to contain greater than or equal to 20 ng aflatoxins/g when, after exactly 1 min, no color was observed on the filter; when a blue or gray color developed, the test sample was judged to contain less than 20 ng aflatoxins/g. All collaborators correctly identified naturally contaminated corn and raw peanut positive test samples. No false positives were found for controls containing less than 2 ng aflatoxins/g. The correct responses for positive test samples spiked at levels of 10, 20, and greater than or equal to 30 ng aflatoxins/g (the ratio of B1:B2:G1 was 10:1:3) were 52, 86, and 96%, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Aflatoxin B1↗
PubMedDate not supplied

Negative ion chemical ionization mass spectrometric method for confirmation of identity of aflatoxin B1: collaborative study.

An interlaboratory study of a negative ion chemical ionization mass spectrometric (MS) confirmation procedure for aflatoxin B1 was conducted in laboratories in the United States, England, and West Germany. Twelve partially purified, dry film extracts from naturally and artificially contaminated roasted peanuts, cottonseed, and ginger root containing varying quantities of aflatoxin B1 were distributed to the participating laboratories. The extracts required additional cleanup before MS analysis, using either an acidic alumina column and preparative thin layer chromatography (TLC) or a 2-dimensional TLC procedure. Recovery of purified aflatoxin B1 was influenced by the degree of recovery of sample from acid alumina and/or the TLC plate and incomplete elution of aflatoxin B1 from silica gel. Factors affecting MS confirmation included the purity and recovery of aflatoxin and MS instrument sensitivity. Aflatoxin B1 identity was confirmed in 19.5, 90.9, and 100% of samples containing less than 5, 5-10, and greater than 10 ng aflatoxin B1/g product, respectively, by solid probe introduction using full mass scans. The MS method has been adopted official first action.

Aflatoxin B1↗