Detection of Total Ergot Alkaloids in Cereal Flour and in Bread by a Generic Enzyme Immunoassay Method.

Four sets of polyclonal antibodies against ergot alkaloids ergometrine, ergotamine, α-ergocryptine, and ergocornine were produced and characterized in a competitive direct or indirect enzyme immunoassay (EIA). Standard curve LODs were 0.03 ng/mL (ergometrine EIA) to 2.0 ng/mL (ergocornine EIA). Three EIAs were highly specific, whereas the ergometrine EIA had a broad specificity pattern and reacted, albeit weakly, with all seven major ergot alkaloids and their epimeric forms. Using the ergometrine EIA, a generic test system was established in which total ergot alkaloids are quantified by a standard curve for a toxin mixture composed of three alkaloids that matched the ergot alkaloid composition in naturally contaminated rye and wheat products. Sample extraction with acetonitrile-phosphate-buffered saline at pH 6.0 without further cleanup was sufficient for EIA analysis. The LODs for total ergot alkaloids were 20 ng/g in rye and wheat flour and 14 ng/g in bread. Recoveries were 85-110% (RSDs of 0.1-11.7%) at a concentration range of 50-1000 ng/g. The total ergot alkaloid EIA was validated by comparison with HPLC-fluorescence detection. Although some under- and overestimation by the total ergot alkaloid EIA was observed, it was suitable for the reliable identification of positive samples at 10-20 ng/g and for the determination of total ergot alkaloids in a concentration range between 100 and 1000 ng/g.

A broadly applicable approach to prepare monoclonal anti-cephalosporin antibodies for immunochemical residue determination in milk.

A simple, efficient and rapid method for the synthesis of cephalosporin-protein conjugates was established. These conjugates were used as immunogens to produce monoclonal antibodies (mAbs) and as solid phase antigens in competitive indirect enzyme immunoassays (EIAs). With this generic approach, a novel set of monoclonal antibodies for cephalosporins was prepared, including ceftiofur and cephalexin as well as, reported here for the first time, cefoperazone, cefquinome and cephapirin. All 5 EIAs were highly sensitive, with standard curve IC(50) values of 0.7 (ceftiofur), 1.1 (cefquinome), 5.2 (cephalexin), 13.8 (cefoperazone) and 40.3 ng mL(-1) (cephapirin). Detection limits (IC(30)) ranged from 0.3 (ceftiofur mAb 1D7) to 17.2 ng mL(-1) (cephapirin mAb 2F10). Specificity studies revealed that cephalosporin-antibody binding was strongly determined by the side chain residues of the cephem nucleus. Therefore all mAbs, to some extent, recognized other beta-lactam antibiotics with similar side chain residues. Within the group of cephalosporins approved for use in veterinary medicine, however, the final EIAs were highly selective for their respective antigen, except for the ceftiofur EIA which showed cross-reactions with cefquinome. The applicability of the five assays for drug residue testing in milk was demonstrated. In each EIA the target drug could be determined in milk with high accuracy and precision at concentrations far below the European Union maximum residue limits.

Development of an enzyme immunoassay for the antibiotic cefquinome and its application for residue determination in cow's milk after therapeutical mastitis treatment.

The aim of this study was to develop and evaluate an enzyme immunoassay (EIA) for the cephalosporin antibiotic in milk, in combination with a new microbiological test system (brilliant black reduction test, BRT-P). Polyclonal antibodies against cefquinome were produced in rabbits, using cefquinome-keyhole limpet hemocyanine as the immunogen. These antibodies and a cefquinome-glucose oxidase conjugate were used in a competitive indirect EIA. The detection limit for cefquinome in milk was 1.5 ng ml(-1), recoveries were 80-128% at 4-40 ng ml(-1). Cross-reactivities with other cephalosporins/penicillins were all <1%. The EIA was used to determine cefquinome in incurred raw milk, the BRT-P (detection limit ≈ 20 ng ml(-1)) and a receptor assay (ßeta-s.t.a.r., detection limit ≈ 15 ng ml(-1)) were used in parallel. Five lactating cows, suffering from clinical mastitis, were treated with cefquinome by simultaneous intramammary and intramuscular injection. Cefquinome residues (maximum 10-27 µg ml(-1)) were most exclusively found in the udder quarter which was treated intramammary, residue levels in the other three quarters were low (<20 ng ml(-1)). Even in milk from intramammary-dosed quarters, residue levels fell below European Union maximum residue level (MRL, 20 µg kg(-1)) 2 days before the end of the withdrawal period. EIA, BRT-P, and ßeta-s.t.a.r. results showed acceptable agreement for milk samples, but the newly developed EIA is superior in aspects of sensitivity. In conclusion, this is the first one description of immunoassay and microbiological tests capable to determine cefquinome in milk at the MRL in incurred sample material.

Enzyme immunoassay for mycophenolic acid in milk and cheese.

Mycophenolic acid (MPA) was reacted with N-hydroxysuccinimide and conjugated to keyhole limpet hemocyanin (KLH), and to horseradish peroxidase (HRP), respectively. The MPA-KLH was used to produce anti-MPA antiserum in rabbits. A competitive direct enzyme immunoassay (EIA) for MPA was established with anti-MPA antiserum and MPA-HRP conjugate. The mean 50% inhibition and detection limit of MPA standard curves (n = 103) were 197 +/- 67 and 81 +/- 48 pg/mL, respectively. The EIA was specific for MPA and its synthetic 2-morpholinoethyl ester, mycophenolate mofetil (91% relative cross-reactivity). Raw bulk milk and pasteurized milk, with and without beta-glucuronidase pretreatment, were analyzed by EIA. No MPA was found in milk, at a detection limit of 100 pg/mL (recovery 58-66% at 0.125-2 ng/mL). Blue-veined cheese from the German market (n = 53) was analyzed by EIA, and the detection limit was at 0.5 ng/g (recovery 68-79% at 5-100 ng/g). All but two cheeses contained MPA, although mostly (66%) at levels of <10 ng/g. MPA at 400-1200 ng/g was found in Roquefort cheeses. Highest levels (4-11 microg/g) were found in a German soft cheese preparation. MPA levels in mycelium-rich parts of cheese were 3 times higher than in mycelium-free parts.

Experiences with an identification and quantification program for inhibitor-positive milk samples.

Beta-lactam antibiotics (penicillins, cephalosporins) are still the most commonly used antibiotics for dairy cows in Germany. In routine milk testing, according to the German milk quality regulation, a positive result obtained for bulk tank milk by microbiological inhibitor tests needs no further confirmation, but results in reduced milk payment of 0.05 euros kg(-1) for one month. In some cases, however, further identification of the causative agent can be of interest, either if antimicrobial drugs have not knowingly been used recently, or if improper use of such drugs is denied. As a service for milk producers, our laboratory offers further analyses of violative milk samples, aiming at the identification and quantification of the inhibitor(s). In this program, a panel of microbiological inhibitor tests, receptor tests, and enzyme immunoassays (EIA) is used in a step-by-step analysis, which primarily focusses on beta-lactams, but also includes other compounds such as sulfonamides or tetracyclines, respectively. Here we report results for violative milk samples (n=63) analysed between 2003 and 2005. In most cases (95%), beta-lactam antibiotics could be identified, although not always at levels exceeding the respective MRL values. Penicillin G (mostly together with benzylpenicilloyl metabolites) could be identified in 74.6% of all samples. Other compounds identified were, in decreasing order, ceftiofur (11%), ampicillin/amoxicillin (6.3%), isoxazolyl penicillins (3.2%), and sulfonamides (1.6%). The results indicate that penicillin G is still the predominant antibiotic responsible for violative bulk tank milk samples as detected during regulatory control.