Mechanism of action of rifampicin is?

R ifampin (Rifampicin, R) It is a semisynthetic derivative of rifamycin B obtained from Streptomyces mediterranei. Rifampin is bactericidal to M. tu berculosis and many other gram-positive and gram-negative bacteria like Staph. aureus, N. meningitidis, H. influenzae, E . coli, Klebsiella, Pseudomonas, Proteus and Legionella. Against TB bacilli, it is as efficacious as INH and better than all other drugs. The bactericidal action covers all subpopulations of TB bacilli, but acts best on slowly or intermittently (spuers) dividing ones, as well as on many atypical mycobacteri a . Both extra- and intracellular organisms are affected. It has good sterilizing and resistance preventing actions. Rifampin inhibits DNA dependent RNA synthesis. Probably, the basis of selective toxicity is that mammalian RNA polymerase does not avidly bind rifampin. Mycobacteria and other organisms develop resistance to rifampin rather rapidly. Rifampin resistance is nearly always due to mutation in the repoB gene (for the beta subunit of RNA polymerase- the target of rifampin action) reducing its affinity for the drug. No cross resistance with any other antitubercular drug has been noted. ESSENTIALS OF MEDICAL PHARMACOLOGY K.D.TRIPATHI SIXTH EDITION PAGE NO:741