New antibiotics, resorcinomycins A and B: antibacterial activity of resorcinomycin A against mycobacteria in vitro.

Resorcinomycin A, N-[(S)-alpha-guanidino-3,5-dihydroxy-4-isopropylphenylacetyl]glyci ne, S-RSM-A, a new antibiotic produced by Streptoverticillium roseoverticillatum, has an antibacterial spectrum directed towards mycobacterial species. It is not active against Gram-negative and Gram-positive bacteria, except mycobacteria and weakly active against mycoplasmas. In vitro activities of the S-, R- and S,R-isomers of RSM-A against atypical mycobacterial strains were compared with those of streptomycin (SM) and kanamycin (KM) by 2-fold agar dilution methods using Middlebrook 7H10 agar medium. Although R-RSM-A and S,R-RSM-A were comparable or inferior to both antibiotics, the antimycobacterial activity of S-RSM-A was superior to that of SM and KM.