MJ347-81F4 A & B, novel antibiotics from Amycolatopsis sp.: taxonomic characteristics, fermentation, and antimicrobial activity.

Strain MJ347-81F4 has been found to produce two new cyclic thiazolyl peptide antibiotics, components A and B. Taxonomic studies including morphological and physiological characteristics and chemical analysis of whole cells of the producing strain revealed this microorganism to belong to genus Amycolatopsis, and so we designated the strain Amycolatopsis sp. MJ347-81F4. After 10 to 12 days of fermentation, most of the antibacterial activity was present mainly in the mycelial cake and reached its maximum level. In comparison with reference compounds, A as the major component showed excellent in vitro activity against gram-positive bacteria including highly methicillin-resistant Staphylococcus aureus (MRSA) and Enterococcus faecalis with MICs in the range of concentration of 0.006 to to approximately 0.1 microg/ml. The results on the antimicrobial activity against thiazolyl peptide-resistant mutants of Bacillus subtilis NRRL B-558 indicated that the possible molecular target of MJ347-81F4 component A might be the 50S subunits of the ribosome, the inactivation of which would inhibit protein synthesis.