A.: Sulfapyridine bacteriostasis of Lactobacillus arabinosus and its

West (1) found that sulfapyridine inhibited the usual curative effect of nico-tinic acid on dogs rendered deficient on a blacktongue diet and that the feeding of fresh liver together with the sulfapyridine gave normal weight responses. He concluded that sulfapyridine might inhibit the action of nicotinic acid but not that of preformed coenzymes. The experimental observations of West have been confirmed by Schaefer, McKibbin and Elvehjem (2) who used a more highly purified basal ration. In addition to comparing the effectiveness of nicotinic acid and fresh liver they also fed equivalent amounts of dried liver and nicotinamide and found them to be inactive. In order to extend these studies, we decided to use the organism Lactobacillu8 arabinosus 17-5 because nicotinic acid is a distinct growth factor for this organism and because we had had considerable experience with the organism in the microbiological determina-tion of nicotinic acid. A number of bacterial studies on the relationship between sulfonamides and nicotinic acid metabolism have been reported. West and Coburn (3) found tha