Submitted to: Food and Agricultural Immunology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/1998
Publication Date: N/A
Interpretive Summary: This study describes the development of a simple, rapid immunoassay for detecting the veterinary drug ceftiofur in milk. Ceftiofur is approved for the treatment of respiratory diseases in cattle, horses, and swine and for treatment of pneumonia in lactating dairy cattle. A quick screening method to detect this residue in meat and milk is highly desirable since this drug can confound standard tests for the presence of other common antibiotic drugs such as penicillin. The immunoassay described is based on previous studies in our laboratory to develop a monoclonal antibody (a protein found in animal blood) that is capable of specifically binding this drug in milk. Thus, the antibody acts as a probe to detect ceftiofur in the milk sample. The assay developed is capable of detecting ceftiofur in the low part per million range and, thus, has application for measuring drug residues. Furthermore, the immunoassay is easier, faster, and more sensitive than the traditional chemical assay that relies on an expensive instrumental system. The simplicity and low cost of the immunoassay makes it a useful tool for producers for the management of their animals and for agencies interested in monitoring for compliance with applicable regulations.
Technical Abstract: Ceftiofur is a potent antibiotic used in veterinary medicine. Recently, we developed a sensitive, monoclonal antibody-based competition enzyme-linked immunoassay (ELISA) for detecting ceftiofur. In lactating dairy cattle, ceftiofur is used for treatment of pneumonia. We report here the application of our previously developed ELISA to the analysis of ceftiofur and of ceftiofur metabolites in milk. In this ELISA, raw milk is simply diluted and added directly into the ELISA. Using ceftiofur standards, the immunoassay has a lower limit of detection, near 1 ppb. Matrix effects in milk require that samples be diluted; thus, ceftiofur levels below 1 ppm were not measured. At fortification levels between 25-2 ppm, an average recovery of 99.8 +/- 18 was observed. Analysis of incurred residues in animals injected daily with therapeutic doses of drug on 5 consecutive days correlated well with studies by others measuring total 14C-ceftiofur residues in animals given the same dose and regime. HPLC analysis of the incurred residue samples only detected a metabolite of ceftiofur, desfuroylceftiofurcystine, at levels below that reported for ceftiofur equivalents in the ELISA. These data suggest that the ELISA is measuring ceftiofur, it's desfuoryl metabolites and conjugates of the desfuoryl metabolite not detected by the HPLC and thus the better correlation with earlier radiolabeled experiments of others.