Lernmaterialien für Microbiology an der Medical Academy of Latvia

1. Exudative lesions

- acute inflammation reaction in lung tissue with edema fluid, PMNL and later macrophages containing Mycobacterium -> resembles bacterial pneumonia

     - may lead into resolution (healing), complete absorbtion of exudate

     - could build massice necrosis of tissue

     - can lead into productive type of lesions

2. Proliferative/productive type lesions - chronic granulomas that prevent spreading of bacteria

Consists of 3 zones:

​(1) central area - large, multinucleated giant cell containing i/c mycobacteria

(2) mid zone of pale epithelioid cells, arragend radially

(3) peripheral zone with Lymphocytes, Monocytes and Fibroblasts

1. Macrophage presents Mycobacterium on MHC-2 to TCR/CD3 on Th0 (naive t helper)

-> binding is stabilised by B7 binding CD4, 3rd signal is IL-12

2. Th0 differentiates into Th1 

-> stimulates release of Interferon gamma = enhances phagolysosome fusion and i/c killing

​-> release of IL-2 -> activation of T cytotoxic with help of macrophage (MHC-1 on TCR/CD3 and B7 on CD28)

3. T cytotoxic effector cell releases perforins and granzymes to destroy Macrophages containing Mycobacterium

4. B cells produces specific Antibody, not much influence as bacteria is mostly i/c

- Muramyl dipeptide -> granuloma formation

- Phospholipids: induce caseous necrosis

- Lipids: cause acid fastness

- Cord factor- inhibits migration of Leukocytes, induces chronic granuloma formation, immunological adjuvant, prevents phagocytosis

- Proteins: cause immune reaction of host (antibodies)

- Test to provide information about hypersensitivity concerning tuberculose

-> detection of specialised Tuberculose T lymphocytes (Effector Th1/Tc; Memory Th1/Tc ) in peripheral blood (negative result for non tuberculose Bacteria and vaccine strains)

- T lymphocytes are challenged with ESAT6, CFP-10, TB7.7 -> release Interferon gamma if positive,

this can be detected by ELISA

- Mononuclear cells are separated, enumerated and used in standardized amounts to prevent false negative results in AIDS patients

Secondary infection/reactivation is caused by remaining Mycobacteria from previous infections 

Consequences:

​- chronic tissue lesions

- formation of tubercle

- caseation 

​-  fibrosis 

- fatigue, weakness, weightloss, fever, night sweats

- chronic cough and spitting blood

​- meningitis, urinary tract involvement in case of no other signs of tuberculosis

-miliary tuberculosis: lesions in many organs (high mortality rate)

- pulmonary, lymphatic, kidney, GIT and bone tuberculosis 

1. Acids fast bacteria (resists decolorization by acid) 

2. Pathogenic species for human: M. tuberculosis, M. africanum, M. leprae, M. bovis

3. Atypical/potentially pathogenic species:

M. avium complex, M. avium, M. intracellulare -> HIV patients are endangered

​4. Leading cause of morbidity/mortalitly in developing countries

5. High resistance due to lipid cell wall: against -> antibiotics, dyes, chemical agents, disinfectant, high temperature, drying 

​- Straight rods, coccoid or filamentous (polymorphic), asporogenic

- Obligate aerobes

- CW structure (responsible for properties):

 -> Complex, lipid rich (including mycolic acids, waxes, phosphatides)

-> Lipids bound to proteins

-> Polysaccharides

Causes: acid fastness, resistance, cord formation, antigenicity, slow growth, delayed hypersensitivity reactions 

Infectious dose: 10 microorganisms in droplets released by sneezing, talking, coughing

1.  Microorganism enters the lungs -> trachea -> bronchi -> alveoli : latent tuberculosis

2. Macrophages engulf Microorganism (resists phagocytosis: inhibition of phago-lysosome fusion and migration of Polymorphoneulcear cells = cord factor!)

-> initiates: Th1 mediated release of cytokines and lymphokines (INF gamma)

3. Resists respiratory burst (due to reactive oxygen) due to lipids (with help of catalase)

-> Exudative tuberculosis may progress into productive tuberculosis

4. Multiplicate within Macrophages, Apoptosis of Macrophages -> Enzym release damages tissue

5. Occurence of lesions after 1-2 months

-> depends on number and virulence of microorganisms and host immune response

6. Development of fibrous tissue, formation of caseous necrosis centers (tubercle)

-> May break into bronchus, empty its content and  form cavity (highly contagious stage)

-> may heal as fibrosis or calcification

7. can spread via blood and lymph to other organs

-> all damage is done by immune reactions/macrophage bursts -> microorganism does not harm by itself

-Rapid (4- 10days) -> M.smegmatis, M. fortitium (saprophytic forms: faster, more pigments, less acids compared to pathogenic)

-Very slow (8 weeks) -> M. tuberculosis

- non growing on artificial media -> M.leprae

Primary infection:

acute exudative lesions with rapid spread via lymphatics by Macrophages -> heals rapidly

-> massive caseation of lymph node (calcification -> Ghon lesion)

- Resistance and hypersensitivity are induced by first infection 

Screening methods are tuberculin test and Interferon gamma release assay

Tuberculin/Mantoux test:

- Purified protein derivate obtained from old tuberculin 

-> injection into tissue of forearm, 5TU tuberculin units, result after 2 days (positive result in case of  4-6 week after infection)

-> leads to delayed Hypersensitivity (Type 4) reaction via sensitized T cells releasing lymphokines and induce immune reaction)

-> Positive result: allergic reaction of skin

Person has been infected in the past (no information about acute infection or immunity)

Is at risk for secondary infection