The factor which promotes virulence of M. tuberculosis ?

Ans. is 'b' i.e., Cord factor Virulence factors . Virulent strains of tubercle bacilli form microscopic "serpentine cord" in which acid fast bacilli are arranged in parallel chains, cord formation is correlated with virulence. A "cord factor" has been extracted from virulent bacilli with pateroleum ether. It inhibits migration of leukocytes, causes chronic granulomas, and can serve as an immunologic "adjuvant". . Other virulence factors for M. tuberculosis. i) Lipoarabinomannan Facilitates the survival of M. tuberculosis within macrophages. ii) Kat G --> Encodes for catalase, an enzyme protective against oxidative stress. rpoV --> The main sigma factor initiating transcription of several genes. iv) erp gene --> Encoding a protein required for multiplication. v) Virulence has been linked paially to the bacterium's lipid rich cell wall and to its glycolipid capsule, both of which confer resistance to complement and free radicals to the phagocytes. Following gene which contribute to virulence have been added in 18"Ve of Harrison . Region of difference- 1 (RD-l) :- Encodes for early secretory antigen- 6 (ESAT-6) and culture filterate protein- 10 (CPF-10) . LeuD, Pan CD and isocitrate lyase gene (icl 1) . Sigma factor C(sig C) and Sigma factor H (sig H) genes . Car D gene Remember . The major factor in virulence of M. tuberculosis is its ability to survive within macrophages.