Milk Components Inhibitory to Bacillus stearothermophilus

Abstract

The growth of Bacillus stearothermophilus NCA 1518 Smooth was inhibited by raw and mildly heated milks. Ten additional strains of thermophilic bacilli were surveyed for sensitivity to the inhibitory components in milk. Six strains were inhibited, two were unaffected, and two were stimulated by sodium caseinate. Inhibition, a property of all milks tested, was independent of stage of lactation and increased with the protein content. Upon fractionation of milk, the major portion of total inhibitory activity remained in the acid insoluble (pH 4.6) curd. Red protein prepared from the casein fraction of milk had a high specific inhibitory activity. Basic proteins and polypeptides such as protamine sulfate, calf thymus histone, and poly-L-lysine also inhibited the test organism. © 1968, American Dairy Science Association. All rights reserved.