AGAROSE-GEL ELECTROPHORETIC DETECTION OF 6 BETA-LACTAM ANTIBIOTIC RESIDUES IN MILK

An electrophoretic method coupled with bioautography was developed for detection and identification of penicillin G, ampicillin, amoxicillin , cloxacillin, cephapirin, and ceftiofur residues in milk. The method uses a 2% agarose gel for electrophoresis, an overlay of PM indicator agar seeded with Bacillus stearothermophilus var, calidolactis, and in cubation at 55 degrees C for 16-18 h. The new method separated and det ected residues in milk at the levels of concern for the Food and Drug Administration (FDA) for penicillin G (5 ppb), cephapirin (20 ppb), an d ceftiofur (50 ppb). The method also detected ampicillin, amoxicillin , and cloxacillin at 20, 30, and 30 ppb, respectively, but these level s are above those of concern for FDA (10 ppb).