STUDIES ON DISC ASSAY METHODS FOR DETECTION OF ANTIBIOTICS IN MILK

Abstract

Studies on disc-assay procedures for detection of milk-borne antibiotics indicated that the “quick” test could regularly detect 0.05 unit penicillin per ml of milk if: (a) petri plates were poured with 5 ml of Penassay agar seeded with at least one but not more than 10 million spores of Bacillus subtilis per ml and (b) an incubation of 3 to 4 hr at 98 F. was used. Storage of poured plates (with Penassay agar) at 40 F. for 72 hr or use of plastic instead of glass petri plates did not reduce sensitivity of the test. A procedure found suitable for detection, in milk, of relatively low levels of antibiotics other than penicillin is based on: (a) use, per petri dish, of 5 ml. Penassay agar seeded with 100,000 to 1,000,000 spores of B. subtilis per ml and (b) an incubation at 72 F. for 16 to 18 hr.