Microbiology and Immunology 2500A/B Lecture Notes - Lecture 22: Mycobacterium Tuberculosis, Methylene Blue, Cell Envelope
14 Nov 2016
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Causes tuberculosis in cows, rarely in humans. Humans can be infected by the consumption of unpasteurized milk leading to extrapulmonary tuberculosis. Can cause a tuberculosis-like illness in humans, particularly in aids patients. First isolated by robert koch in 1882. M. tuberculosis can be grown in the lab on specialized media but takes 4-6 weeks to. Mycobacteria have an unusual cell envelope with high concentrations of mycolic get small colonies acid (cid:494)waxy(cid:495) This unusual cell envelope is associated with resistance to: Lethal oxidative stress promoting survival inside of macrophages. Impermeability to stains and dyes (cid:494)gram positive(cid:495) acid fast stain (cid:523)a (allmark of mycobacteria(cid:524) The waxy, lipid-rich cell envelope (very hydrophobic) resists common strains (cid:498)acid-fastness(cid:499) is due to the presence of mycolic acid (ie. gram strain) Stained with carbol-fuchsin dye with slow heating (to melt the wax) Acid-fast organisms appear red whereas non-acid fast organisms appear blue.
