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The Use of 2,3,5-Triphenyltetrazolium Chloride as a Test for Antibiotic Substances in Milk¹

Department of Dairy and Food Industries, University of Wisconsin

ABSTRACT

A simple test for detection of inhibitory substances in milk is outlined. The test is based on the conversion of 2,3,5-triphenyltetrazolium chloride (TTC) to formazane. The reaction is characterized by a color change from the leucoform to red in the presence of growing bacterial cells. This conversion is inhibited by antibiotics at low levels of concentration. When S. thermophilus is used as a test organism, penicillin at 0.04 unit, aureomycin at 0.2 , terramycin at 0.25 , and streptomycin at 4.0 per milliliter can be detected in raw milk. The total time for the test is 2 hours.

¹ Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.