Rapid screening assay for beta-lactam antibiotics in milk: collaborative study.

A 15 min assay for beta-lactam antibiotics has been used by dairies for several years as a screening procedure for testing milk tankers before they unload. The test is based on a competition between 14C-penicillin and beta-lactam antibiotics in the milk samples for sites on a microbial cell wall that specifically binds beta-lactam. In a collaborative study, 11 laboratories correctly distinguished 10 coded zero penicillin G samples and 10 coded 0.01 IU/mL samples. The proposed test is qualitative, positive or negative, and can detect the presence of beta-lactam antibiotics at the 0.01 IU/mL level. The control point for determining positive or negative samples is more than 3 standard deviations from the mean of 0.01 IU/mL. The method has been adopted official first action.