Etamycin B

Griseoviridin, a known antibiotic produced by Streptomyces cacaoi subsp. cacaoi, was found to be active against Brachyspira hyodysenteriae--the bacterium causing swine dysentery. An in vitro synergism is observed when it is used in combination with viridogrisein--a simultaneously produced antibiotic. In mouse experiments, the effect of griseoviridin alone was less than that of lincomycin--a commercially available swine dysentery medication. However, a 1:1 mixture of griseoviridin and viridogrisein revealed a noticeable synergistic effect. In an evaluation using pigs artificially infected with B. hyodysenteriae, a large difference was not observed between the effect of griseoviridin alone and that in combination with viridogrisein. Nevertheless, griseoviridin alone exhibited a therapeutic effect superior to that of lincomycin.

We describe the actinomycete strain IMV-70 isolated from the soils of Kazakhstan, which produces potent antibiotics with high levels of antibacterial activity. After the research of its morphological, chemotaxonomic, and cultural characteristics, the strain with potential to be developed further as a novel class of antibiotics with chemotherapeutics potential was identified as Streptomyces sp. IMV-70. In the process of fermentation, the strain Streptomyces spp. IMV-70 produces the antibiotic no. 70, which was isolated from the culture broth by extraction with organic solvents. Antibiotic compound no. 70 was purified and separated into individual components by HPLC, TLC, and column chromatography methods. The main component of the compound is the antibiotic 70-A, which was found to be identical to the peptolide etamycin A. Two other antibiotics 70-B and 70-C have never been described and therefore are new antibiotics. The physical-chemical and biological characteristics of these preparations were described and further researched. Determination of the optimal growth conditions to cultivate actinomycete-producer strain IMV-70 and development of methods to isolate, purify, and accumulate preparations of the new antibiotic no. 70 enable us to research further the potential of this new class of antibiotics.

LC-MS and LC-MS/MS analyses indicated that an enzyme responsible for inactivating the antibiotic etamycin is specific for streptogramins and acts on both type B-I and B-II streptogramin subgroups. No enzymatic activity was detected for other cyclodepsipeptides such as surfactins and viscosin. It was demonstrated using analogs of etamycin that the picolinyl moiety is essential to obtain enzyme-generated ring-opened compounds. Because the picolinyl moiety is also essential for the biological activity of streptogramins, it is proposed that this residue is a distinctive topographic feature in the binding of this group of antibiotics to enzyme active sites.