Biosensor analysis of beta-lactams in milk: comparison with microbiological, immunological, and receptor-based screening methods

Two recently developed surface plasmon resonance biosensor assays for detection of beta-lactams in milk were used to screen raw producer milk samples. Both assays use a beta-lactam receptor protein with carboxypeptidase activity for detection. The results of the biosensor assays were compared with those of various commercial screening tests, i.e., the Delvotest SP, Penzym S, Beta-STAR, SNAP, and Parallux. The results of the 2 biosensor assays showed good agreement with those of the other screening tests. Of 195 analyzed milk samples, the results of only 5 samples differed between the assays. Additionally, 30 milk samples with both negative and positive results in the screening assays were analyzed by liquid chromatography for identification and quantification of any beta-lactam residues. All screening tests showed 0% false-negative results with 15 incurred samples containing between 4.0 and 268 microg/kg penicillin G. The biosensor assays showed 27% positive results (false violatives) with 15 producer milk samples containing penicillin G concentrations between 0 and 3.6 microg/kg, i.e., below maximum residue limit. This figure varied between 27 and 53% for the other screening tests.