This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Chemotherapy, Subject name: Pharmacology
Mechanism of action of rifampicin is? 
Select and explain. 
A. Inhibition of mycolic acid synthesis, B. DNA dependent RNA polymerase inhibition, C. Protein synthesis inhibition, D. Inhibits synthesis of arabinogalactone
B: DNA dependent RNA polymerase inhibition
Answer: B: DNA dependent RNA polymerase inhibition 
Explanation: 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