The growth of L. fermenti 36 which requires thiamine for its growth was inhibited by thiamine sulfuric acid ester but not the growth of L. arabinosus and L. casei which requires no thiamine. The inhibition of thiamine sulfuric acid ester for L. fermenti was recovered competitively and specifically by thiamine, and its inhibition index was 1,000-1,500. The compound had no thiamine activity.
