TB I

Question 1

Bacteria responsible for TB

Answer 1

mycobacterium u=tuberculosis

Question 2

What causes leprosy

Answer 2

Mycobacterium leprae

Question 3

Non-Tuberculous Mycobacteria causes what infections?

Answer 3

Opportunistic infections in immunocompromised patients, but not TB

Question 4

Explain the Mycobacterium Tuberculosis complex

Answer 4

TB is caused by a family of closely related species, including Mycobacterium bovis (infecting cattle).
However Mycobacteria tuberculosis is the most prominent in this complex

All members of this family can cause tuberculosis in humans and or animals

Question 5

structural features of mycobacteria

Answer 5

Cell wall with high lipid content - hydrophobic
Cell wall contains 60% mycolic acids -Long chain fatty acids

Question 6

How does mycobacteria stain with Gram stain?

Answer 6

Doesn’t stain with conventional Gram stain: absent/only a ghost outline of mycobacteria. It requires special stains

Question 7

How to encourage entrance of stain into the cell?

Answer 7

Use special stains and heating during the staining process, followed by the decolourisation step with acid and alcohol

Question 8

Why are mycobacteria called acid fast?

Answer 8

The decolourisation step with acid and alcohol usually removes stain from ordinary bacteria.
But mycobacteria hold onto the stain  they are ACID AND ALCOHOL – FAST

Question 9

Microscopic lab characteristics of mycobacteria (6)

Answer 9

Slender (thin) straight or slightly curved bacilli (also sometimes called rods)
* Aerobic
* Slow growing – multiplies and divides only about every 24 hrs compared to E. coli which divides
every 30 minutes
* Resistant to drying and to many chemical disinfectants
* Sensitive to UV light
* Sensitive to sustained heat

Question 10

what cell types are commonly found in chronic inflammation?

Answer 10

Lymphocytes, plasma cells macrophages

Question 11

why does mycobacteria cause chronic inflammation?

Answer 11

Oneof the causes of chronic inflammation is infection with mycobacteria and other organisms that are
resistant to phagocytosis and intracellular killing

Question 12

What special type of chronic inflammation is caused

Answer 12

granulomatous inflammation

Question 13

6 key concepts of TB pathogenesis

Answer 13

. Intracellular pathogen
2. Primary host cell in humans is the macrophage
3. Require cell mediated immunity to control infection
4. Characteristic pathological feature of tuberculosis is granulomatous inflammation or the
formation of necrotising granulomas
5. Potentially lifelong infection
6. Outcome of infection with TB is a continuous balance between the host’s immune control and
the virulence of the mycobacteria

Question 14

pathogenesis of TB

Answer 14

Occurs on first exposure to TB bacilli
* Following inhalation TB bacilli are phagocytosed by alveolar macrophages
* Normally phagocytosis leads to killing of micro-organism that has been engulfed
* But TB bacilli manage to upset this normal killing: they are not killed and in fact TB bacilli can multiply inside macrophages

Question 15

How is cell mediated immunity activated in during TB pathogenesis

Answer 15

• Inside macrophages TB bacilli are transported via lymphatics to regional (hilar) lymph nodes
• In the lymph nodes TB bacilli stimulate an immune response, mainly by the cell mediated immune response :
• Infected macrophages present TB antigen to lymphocytes
• TB-specific lymphocytes proliferate and produce various cytokines including
• Interferon-gamma
• Tumour necrosis factor (TNF)

Question 16

What is the functions of the cytokines released by the TB specific lymphocytes?

Answer 16

Cytokines activate macrophages and increase their ability to kill the mycobacteria by the formation of granulomas

Question 17

What does a granuloma consist of?

Answer 17

Central area of necrosis
* Surrounded by activated macrophages (some of which may fuse together to form giant
cells) Note activated macrophages also called epitheliod cells
* Surrounded on outside by T lymphocytes and fibrous tissue
* The granuloma contains the organism by walling it off

Question 18

After some time, he material within the granulomas becomes necrotic and__________

Answer 18

caseous

Question 19

How does primary TB infection heal?

Answer 19

In most cases the tubercles /small granulomas heal spontaneously
* Sometimes form a scar or even calcify
* May show up on CXR as nodule especially if calcified

Question 20

How long does primary infection take to heal?

Answer 20

3-6 weeks

Question 21

Explain latent TB

Answer 21

Dormant TB. The mycobacteria from primary infection did not all die, some remain dormant causing latent TB.

potential to reactivate when immunocompromised

Question 22

what is progressive primary disease?

Answer 22

in a minority of people, mycobacteria are not contained within the primary complex, at the time
of primary infection or within the next 1-2 years but spread causing ‘progressive primary
disease’
* Spread can be by local extension or via bloodstream or lymphatics

Question 23

Progressive primary infection results in what?

Answer 23

Result in:
* more extensive lung disease
* foci of infection in almost any site of the body which can develop into disease immediately or
at some stage in the future
* disseminated disease in many organs – called ‘miliary’ tuberculosis

Question 24

What is secondary TB?

Answer 24

Due to reactivation of dormant mycobacteria, usually due to declining immune system

Question 25

Causes of secondary TB

Answer 25

• Usually because of declining immune system, e.g.
• HIV
• Malnutrition
• Chemotherapy for treatment of malignancy
• Other immunosuppressive medication, e.g. high dose steroids, medication to prevent
  rejection after organ transplant, people being treated with anti-TNFα medicines
• Old age

Question 26

Where does reactivation of Tuberculosis normally occur? Why?

Answer 26

In Apex of lungs. Because this part is highly oxygenated compared to other parts of the lung, allowing the bacteria to multiply more rapidly (because the bacteria is aerobic)

Question 27

What is the process of 2ndary TB in the lung?

Answer 27

With secondary disease, get formation of granulomas again with caseous necrosis
* Can result in formation of cavities within lung, which often contain large numbers of TB bacilli
* If these cavities connect to the bronchi, can lead to expectoration (coughing up) of TB bacilli
with increased risk of transmission to other people
* Infection can spread to other sites in the lung, or to more distant sites in the body

Question 28

Different types of TB lesions in Primary, secondary, and miliary TB

Answer 28

Primary tuberculosis (TB) produces a small midzone
lesion
with involvement of hilar lymph nodes.
[B] In secondary TB, the lesions are usually apical and
often bilateral.
[C] In miliary TB, the lungs and many other organs contain
numerous small granulomas.

Question 29

What are the common complications of pulmonary TB?

Answer 29

The most frequent complications are intrapulmonary or
pleural spread.

Question 30

What is the least complication of TB?

Answer 30

Miliary disease and intestinal disease

Question 31

Describe miliary TB

Answer 31

Miliary TB is a serious infection where there is widespread dissemination of TB, with lots of small granulomas in many organs. The granulomas contain numerous mycobacteria

Question 32

Where are the lesions of pulmonary TB commonly found?

Answer 32

lungs, meninges, kidneys, bone marrow and liver