- Muramyl dipeptide (from peptidoglycan NAG, NGM- N-glicolmuramic acid) complexed with mycolic acids can cause granuloma formation- Phospholipids induce caseous necrosis- Lipids are responsible for acid-fastness.- A "cord factor" (trehalose-6,6`-dimycolate) is a virulence factor → inhibits migration of Leu, causes formation of chronic granulomas, serves as an immunologic "adjuvant", cytotoxic properties- no exotoxins- Proteins that elicit the tuberculin reactionTheir role in the pathogenesis of infections:- High resistance to penicillin- resistance of phenol (disinfectant)- Resistant to drying- Mycobacteria in droplets are inhaled when infected person cough, sneeze, or speak → Reach alveoli → phagocytosis → stimulate host Mo and M/ph → mycobacteria begin to multiply within M/ph → Some of the M/ph develop the ability to kill → Later, peripheral fibrous tissue develops, and the central area undergoes caseation necrosis (such lesion is called a tubercle) → A caseous tubercle may break into a bronchus, empty its contents there → and form a cavity → it may subsequently heal by fibrosis or calcification- Spread trough the lymphatics → blood stream and finally all organs1. Exudative type:- Consist of acute inflammatory reaction in lung tissue with edema fluid, PMNL (polymorphonuclear leukocytes) and later monocytes appear around the tubercle bacilli (resemble bacterial pneumonia)- Outcomes of this lesions:→ may heal by resolution, entire exudate becomes absorbed→ may lead to massive necrosis of tissue→ may develop into second (productive) type of lesion2. Productive (proliferative) type of lesion:- When it is fully developed, this lesion is chronic granulomawhich consists of 3 zones;→ central area of large, multinucleated giant cells containing intracellular mycobacteria→ mid zone of pale epithelioid cells, arranged radially→ peripheral zone (outer zone) of fibroblasts, lymphocytes andmonocytes- Granuloma prevents further spread of bacteria!- Later, peripheral fibrous tissue develops and the central area undergoes caseation necrosisàsuch lesion is called tubercle!

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