Mycobacteria

Question 1

Give three examples of mycobacteria:

Answer 1

1- M. tuberculosis
2- Atypical mycobacteria
3- M. leprae

Question 2

Explain the acid fast staining procedure

Answer 2

1- smear sample on glass slide
2- Dye with Carbofuchsin
3- Steam over boiling water
4- Cool and decolorize with Alcohol
5- Rinse with water to stop decolorization
6- Counterstain with methylene blue
7- Rinse
8- Blot dry and examen

Question 3

What color do acid fast bacteria show up on an acid fast stain?

Answer 3

pink

Question 4

What is a distinctive feature of acid fast bacterial cell wall?

Answer 4

mycolic acids and arabinogalactan

Question 5

What type of respiration do mycobacteria undergo?

Answer 5

obligate aerobes

Question 6

Do mycobacterium grow in culture?

Answer 6

M. tuberculosis can, but grows VERY slowly!

M. leprae cannot grow in cultre

Question 7

What does M. tuberculosis need to grow in culture?

Answer 7

Time and special nutrients

Question 8

Is M. tuberculosis an intracellular or extrcellular pathogen?

Answer 8

Both

Question 9

Where is M. tuberculosis drug resistance encoded?

Answer 9

plasmids (easy transfer)

Question 10

What are three main virulence factors of M. tuberculosis? And what is the function of each factor?

Answer 10

1- Mycolic acid (helps evade the immune system)
2- Phosphatides (stop necrosis)
3- Cord factor (contributes to virulence)

Question 11

Describe the ID of M. tuberculosis:

Answer 11

Extremely low ID50. Less than 10 organisms needed for infection

Question 12

What is the pathogenesis of TB?

Answer 12

1- Inhalation of infected particles
2- Alveolar macrophages phagocytose the bacteria
3- Bacteria prevents the fustion with a lysozome
4- Bacteria uses macrophage as a trojan horse
5- Bacteria can proliferate in macrophage and continue to cause disease (systemic)

Question 13

What types of symptoms can M. tuberculosis cause when they proliferate in macrophages?

Answer 13

1- Exudative lesions
2- Granulomatous lesions
3- Tubercule
4- Reactivation lesions

Question 14

What are exudative lesions?

Answer 14

These are typically found in the lungs/ initial site of infection with TB. It is an acute inflammatory response of a Ghon complex.

Question 15

What is a ghon complex?

Answer 15

exudative lesion and draining lymph nodes

Question 16

What is a tubercule?

Answer 16

this is an older granuloma that is surrounded by fibrous tissue and has a central caseation necrosis

Question 17

How does a tubercule heal?

Answer 17

fibrosis and calcification

Question 18

What allows lesions to be reactivated?

Answer 18

immunosuppression or infection with Measles, varicella, or pertussis

Question 19

Where can reactivation lesions occur?

Answer 19

neck, kidney’s, brain, spine, lower lung

Question 20

How is an infection with M. tberculosis controlled by the immune system?

Answer 20

cell mediated immunity. CD4 helper t cells activate some infected macrophages to kill intracellular bacteria and CD8 t cells lyse other infected macrophages

Question 21

What is the result of the cell mediate immune response to tuberculosis infection?

Answer 21

caseating granuloma (latency)

Question 22

What is an important factor in maintaining latency?

Answer 22

TNF-alpha

Question 23

What are the different presentations of TB infection?

Answer 23

1- Classic active pulmonary TB
2- TB scrofula
3- GU TB
4- CNS TB
5- Skeletal TB
6- GI TB
7- Miliary TB
8- TB memingitis

Question 24

What is indicative of classic active pulmonary TB?

Answer 24

cavity formation in the lung, fever, night sweats, weightloss, cough

Question 25

What is TB scrofula and what is indicative of this condition?

Answer 25

This is reactivation of TB in a lymph node

Symptoms include a painless, enlarging, or persistent mass. Usually the cervical lymph nodes.

Question 26

What is the most common etrapulomary site of TB infection? And what are the symptoms?

Answer 26

GU Track

Reaches the kidneys but can be latent for 20 years

Question 27

How is CNS TB diagnosed?

Answer 27

MRI and spinal tap

Question 28

What are the two main manifestations of skeletal TB?

Answer 28

joint arthrtitis and potts diease

Question 29

How does pott’s disease present?

Answer 29

back pain, stiffness, paralysis or lower extremities

Question 30

What is a major symptom of GI TB?

Answer 30

obstruction or hemorrhage of the iliocecal region

Question 31

What is miliary TB?

Answer 31

Hematogenous spread of TB throughout the body. There are many tiny NON-calcified foci of infection in the lungs.

Question 32

When is miliary TB most likely to occur?

Answer 32

After a primary infection, rather than during reactiviation

Question 33

What is a diagnostic sign of TB meningitis?

Answer 33

Brudziniski’s sign (cranial nerve palsies)

Question 34

What is the difference between a PPD for TB and one for leprosy?

Answer 34

TB tests exposure whereas leprosy tests you immune response

Question 35

What are the typical characteristics of atypical mycobacteria?

Answer 35

Acid fast wall, do not cause TB or leprosy, usually environmentally acquired

Question 36

How many groups of atypical TB is there?

Answer 36

4 main groups

Question 37

What is the reservoir for M. leprae?

Answer 37

Humans and armadillos

Question 38

What is the pathogenesis of M. leprae?

Answer 38

unclear transission method with an extremely long incubation period.

Question 39

What type of cells does M. leprae cause an intracellular infection?

Answer 39

skin histocyes, endothelial cells, schwann cells

Question 40

what are the two forms of leprosy? What is the difference between the two ?

Answer 40

Tuberculoid leprosy and Lepromatous leprosy

Tuberculoid is a strong CMI response with few bacilli. There is typically immunogenic nerve damage and granuloas form

Lepromatous leprosy is a poor CMI response with a lot of bacilli. Nerves are damaged by bacteria and foamy histocytes form