Detection of Beta-Lactam Antibiotics in Bulk Tank Milk

A total of 100 raw bulk tank milk samples were tested using both the Delvotest-P agar diffusion test and the Delvo-X-Press enzyme linked immunosorbent assay (ELISA) test for beta-lactam antibiotics. Samples were spiked with various levels of different beta-lactams and detection levels were compared to the manufacturer's reported sensitivities and safe levels currently published for raw milk in Canada's Food and Drugs Regulations. In all cases, both tests met or exceeded the reported test sensitivities and all currently published safe levels, with the exception of cloxacillin on the Delvo-X-Press test only. Current safe levels for cloxacillin are 30 ng/ml; this test only detected levels of 70 ng/ml, despite the manufacturer's claim of 50 ng/ml. No false-positive or -negative samples were found using either test method. Both tests were easy to perform, but the Delvo-X-Press required more technical ability. In view of the decreased detection time offered by the Delvo-X-Press (10 min) (Delvotest-P, 2.5 h) and the test's simplicity, this test should be considered as a screening test on the dairy loading dock before milk is accepted into the plant. In addition, the Delvo-X-Press offers an increased shelf life compared with other ELISA tests, because of the separate packaging for test reagents, which is certainly advantageous for infrequent testing.