Studies on Tetracycline-resistant Escherichia coli Strains and a Growth-requirement for 1-Histidine

1. A tetracycline-resistant E. coli, which had been selected by a laboratory technic, was found to have a specific requirement for 1-histidine. 2. Urocanic acid, imidazole and 5 analogs, 1-histidinol, and 1-histi-dinal were unable to substitute for 1-histidine, nor were they able to antagonize the activity of tetracycline against the parent E. coli (tetracycline-sensitive) in synthetic medium. 3. Twenty E. coli strains, all tetracycline-resistant and isolated from clinical sources were obtained. None had the specific requirement for 1-histidine.