A monoclonal antibody‐based immunoassay for the detection of ceftiofur in milk

Abstract

Ceftiofur is a potent antibiotic used in veterinary medicine. Recently, we developed a sensitive, monoclonal antibody‐based competition ELISA for detecting ceftiofur. In lactating dairy cattle, ceftiofur is used for the treatment of pneumonia. We report here the application of our previously developed ELISA to the analysis of ceftiofur and its 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, however, require that samples be diluted and thus ceftiofur levels below 1 ppm were not measured. At fortification levels between 25 and 2 ppm, an average recovery of 99.8 ±18 was observed. Analysis of incurred residues in animals injected daily with therapeutic doses of drug for 5 consecutive days correlated well with studies by others measuring total l4C‐Ceftiofur residues in animals given the same dose and regime. High‐performance liquid chromatography (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 the ceftiofur, in addition to its desfuoryl metabolites and conjugates of the desfuoryl metabolite not detected by the HPLC and thus the better correlation with the earlier radiolabeled experiments of others.