Antibiotic strains of streptomyces can be classified according to their antibacterial spectra around their colonies growing on the nutrient agar, as described in the previous paper, and it can be easily estimated what kinds of antibiotic substances are produced by them. The strains, isolated by us and inhibiting the growth of E. coli, were classified to streptomycin-producing group, streptothricin-group-substances-producing group, geisein-producing group, chloromycetin-producing group, and the fourth group which chiefly produces streptothricin-group-substances. But during further studies we found a strain showing a new antibacterial spectrum and a yellow crystalline antibiotic substance was extracted. It inhibits both the growth of gram positive and that of gram negative bacteria.
Among antibiotic substances obtained from streptomyces, aureomycin and xanthomycin which were recently found are reported to be yellow colored. Though we do not know the details of these substances, they seem to be different from the substance in this paper. Besides we can not find the species in literature which is identical with the strain No. 26A producing the antibiotic substance described in this paper, though it seems to be most resembling to Actinomyces farcinicus or Streptomyces lipanii. So we decided to call the antibiotic substance Aureothricin.