ABSTRACT
<p><b>OBJECTIVE</b>To develop a rapid multi-residue assay for detecting 16 demanded by the European Union (EU).</p><p><b>METHODS</b>A recombinant penicillin-binding protein (PBP) 2x* from Streptococcus pneumoniae R6 was expressed in vitro and six β-lactams were conjugated to HRP by four methods. A rapid multi-residue assay for β-lactams was established with PBP2x* and HRP-conjugate.</p><p><b>RESULTS</b>PBP2x* was expressed and purified successfully and the ideal HRP-conjugate was identified. The multi-residue assay was developed. After optimization, penicillin G, ampicillin, amoxicillin, cloxacillin, dicloxacillin, oxacillin, nafcillin, cephalexin, ceftiofur, cefalonium, cefquinome, cefazolin, cefoperazone, cephacetrile, and cephapirin can be detected at levels below MRL in milk with simple pretreatment.</p><p><b>CONCLUSION</b>This assay developed can detect all 16 β-lactams demanded by the European Union (EU). The whole procedure takes only 45 min and can detect 42 samples and the standards with duplicate analysis.</p>