ENZYME-IMMUNOASSAY FOR THE DETECTION OF ISOXAZOLYL PENICILLIN ANTIBIOTICS IN MILK

Polyclonal antibodies were raised against isoxazolyl penicillins in ra bbits after immunization with a cloxacillin-human serum albumin conjug ate. The antisera were tested in direct and indirect competitive enzym e immunoassays (EIAs), using glucose oxidase or horseradish peroxidase conjugates of oxacillin, cloxacillin, or dicloxacillin, respectively, as the labelled antigen. The relative cross-reactivities of each test system with oxacillin, cloxacillin, and dicloxacillin, determined fro m the amount of antibiotic required for 50% inhibition of labelled ant igen binding, were dependent on the antibiotic used as the labelled an tigen. Other beta-lactam antibiotics did not cross-react in these test systems. In a direct EIA using a cloxacillin-horseradish peroxidase c onjugate, cloxacillin and dicloxacillin in milk were detected at level s of 10 and 30 ng ml(-1); the average recoveries at these levels were 102 and 84%, respectively.