Macrolide antibiotics M-4365 produced by Micromonospora. IV. Antimycoplasmal activity of antibiotic M-4365 G2 (de-epoxy rosamicin).

In vitro activities of M-4365 G2, a new basic 16-membered macrolide antibiotic, against a total 19 strains including human, bovine, porcine, rodent, avian and saprophytic mycoplasmas were compared with those of three other macrolide antibiotics, josamycin, erythromycin and tylosin. M-4365 G2 exhibited stronger activities than the other macrolide antibiotics against 11 strains of mycoplasma tested. Especially, its higher activities against M. pneumoniae Mac and FU, U. urealyticum T-960, M. mycoides PG-1 and M. gallisepticum Kp-13, PG-31 and 9-49A were to be noticed (final minimum inhibitory concentrations: 0.0001 approximately 0.049 microgram/ml). Higher antimycoplasmal activity of M-4365 G2 than that of tylosin was also proved in experimental treatment of chickens intranasally inoculated with M. gallisepticum Kp-13 by feeding a diet containing the drug. M. gallisepticum Kp-13 was not isolated from the infected chickens fed a diet containing 0.0063% or more of M-4365 G2.