Abstract: The penicillin-binding protein PBP 2x from Streptococcus pneumoniae was utilized to develop a novel microplate assay for the determination of ceftiofur with intact β-lactam structure in milk. The assay was developed as screening test with the option for a quantitative assay for ceftiofur residues. Ceftiofur could be detected at levels corresponding to 1/5 EU maximum residue limit(MRL) in milk without lengthy and elaborate sample pre-treatment. Matrix calibration curves are presented, which show that quantitative analyses are possible.

Key words: Milk, Ceftiofur, Receptor binding assay, Enzyme-linked immunosorbnent assay