Detection of sulfa drugs and antibiotics in milk

A disc assay method for testing sulfa drugs and antibiotics in milk was developed wherein Bacillus megaterium ATCC 9855 was used as the test organism and Mueller-Hinton agar was used as the test substrate. Incubation was at 37 C for 4 to 5 hr. The test procedure is an improvement over the Bacillus subtilis-Antibiotic Medium No. 1 method, as described in Standard Methods for the Examination of Dairy Products, in that it is sensitive to eight sulfa drugs and to bacitracin without a significant change in sensitivity to eight other antibiotics commonly used for mastitis therapy.