Search for Antibiotics Active Against Mycobacterium tuberculosis. 1. A. Streptothricin-like Antibiotic from a Streptomyces sp. ∗

Abstract

In a search for antibiotics active against Mycobacterium tuberculosis var. hominis several hundred antagonists have been encountered and one called Streptomyces sp. EI₅ in our records was chosen for intensive study because of its marked activity against the mycobacteria and the low animal toxicity of its crude filtrate. 1 The present report is the account of a study of this organism and the antibiotic it produces.

Methods and Results. A. Morphological and Cultural Characteristics of Streptomyces sp. EI_5. Since preliminary tests of solubility and antibacterial activity indicated that the antibiotic produced by S.spEI₅ is similar to streptomycin and streptothricin, a comparison of the organisms that produce these antibiotics was made.

Streptomyces sp. EI₅ was morphologically similar to Streptomyces griseus, and both organisms produced a soluble yellow to yellow-brown pigment when grown at room temperature on nutrient agar, glucose agar, starch agar, and gelatin. Only S. griseus produced pigment on potato agar. The color of the aerial mycelium varied from white to tea-green with S.griseus and from white to gray with S. sp. EI₅. The vegetative mycelium of S. griseus was white to cream colored and that of S.sp. EI₅ yellow to tannish orange. Streptomyces sp. EI₅ was not susceptible to the S. griseus actinophage of Reilly, Harris and Waksman. 2 These observations indicate that S. griseus and S. sp. EI₅, are similar but significantly different organisms.

Streptomyces lavendulae produced a darker brown pigment on glucose agar, nutrient agar and glucose broth than S. sp. EI₅, and in addition produced pigment on the potato plug. Further, slide cultures on Czapek's medium at 30°C showed the aerial mycelium of S. lavendulae to be pink to lavender, and the hyphae often coiled terminally, in contrast to the white to gray color and the straight hyphae of S. sp. EI₅. The conidia of S. sp. EI₅ were observed to be oval to globose and considerably smaller than those of S. lavendulae. These differences indicate that S. lavendulae and S. sp. EI₅ are not identical.