Evaluation of a modified enzymatic test for the detection of tetracyclinesin milk

The tetracycline galactosidase (TG) test, a new method for the detection of tetracycline residues in raw milk based on the inhibition of beta-galactos idase biosynthesis in Escherichia coli, was previously validated with spike d milk samples. It has now been applied to milk from cows treated with oxyt etracycline. In view of the occurrence of false positives, related to highl y elevated somatic cell counts (>10(6)/ml), the improved TG test was develo ped, in which a heating step (80 degrees C, 15 min) preceded the original T G test protocol. A good agreement with other assays (Delvotest SP, the Baci llus cereus microtiter test, the LacTek tetracycline milk screening test, t he Charm HVS-8100 tetracycline test) as well as with high-pressure liquid c hromatography was obtained. No false negatives were observed with reference to the established maximum residue limit for tetracyclines of 100 mu g/kg milk.