Mycobacterial diseases

Question 1

Does mycobacteria have cells wall

Answer 1

– Unusual waxy cell wall- high lipid content

– Slow growing- different media required

Question 2

3 stains which are commonly used in mycobacterial testing

Answer 2

– Acid fast bacilli (AFBs)
– Ziehl Neelsen (ZN)
– Phenol auramine.

Question 3

what happens in the latent phase of a mycobacterial infection.

Answer 3

– Mycobacterium ingested by macrophages but it cannot be killed so it multiples inside

Question 4

common types of mycobacterium and the infections they cause

Answer 4

• M. Tuberculosis complex: Tuberculosis
– M. Tuberculosis
– M. Bovis- common in animals.
• M. Leprae Leprosy

• “Atypical” Mycobacteria:
– M. Avium complex- HIV associated
– M. Kansasii
– M. Marinum- Fish tank granuloma

Question 5

what chronic infection id M. tuberculosis often seen with

Answer 5

HIV

Question 6

how is TB acquired

Answer 6

droplet spread, inhalation

Question 7

most common site of TB infection within the lung

Answer 7

periphery of lung mid zone.

Question 8

What is ghon focus

Answer 8

swollen lymph nodes and found in midzone.

Question 9

What immune cell plays a major role in TB

Answer 9

macrophages- phagocytoze macrophages but cannot kill it

they then migrate to the lymph nodes

Question 10

what is the body’s response to a tubercle formation

Answer 10

– Granuloma
– Cell - mediated immune response- not antibody.
– Central area of epithelioid cells, giant cells.
– Surrounding lymphocytic cell infiltration.
– Central area caseous necrosis.
– Fibrosis / calcification of lesions
– Bacilli slowly die / may remain viable 20 years

Question 11

what are the symptoms found in primary TB

Answer 11

Influenza - like” syndrome- fever and malaise.

Question 12

what can be seen in the chest x-ray in primary TB

Answer 12

nothing

Question 13

what does the tuberculin skin conversion test show in primary TB

Answer 13

normal initially and then 3 months after infection will be positive.

Question 14

what happens in secondary TB

Answer 14

reactivation of TB

lowered immunity

Question 15

what factors cause the immunity to become compromised which results in secondary TB

Answer 15

– Malnutrition
– Alcoholism
– Debilitating illness
– HIV infection- knocks out T cells so immune system is weak.
– Silicosis, chronic renal failure, gastrectomy..
– Anti TNFα blockade (e.g. infliximab)- TNF maintains granuloma wall containing all the bacteria within it.

Question 16

Where is the most common site to find reactivated TB

Answer 16

• Lung apices

Question 17

most common symptoms of TB

Answer 17

Haemoptysis

• Weight loss, fever, night sweats.

Question 18

what happens to the granuloma/tubercle in secondary TB

Answer 18

cannot maintain granuloma/tubercle so TB spreads.

Question 19

what extra pulmonary sites can be affected by TB

Answer 19

–	Pleura
–	Lymph nodes
–	Kidneys , epididymis
–	Bone- spine
–	Intestines- from swallowing sputum or drinking unpasteurized milk.
–	Brain / meninges
–	Pericardium

Question 20

common symptoms of Tb associated meningitis.

Answer 20

– Unidentified fever
– Personality change
– Focal neurological deficit- this is were the bacteria multiply.
• Basilar inflammation.
– Mild headache / meningism.
– May lack constitutional quartet
• (fever, night sweats, anorexia, weight loss)

Question 21

how is TB diagnosed

Answer 21

– Radiology-Chest X – ray- lesion in upper lung.
– Histology
– Skin testing
– (Blood test: Interferon- γ release assay: IGRA)
– Microbiology.
• Confirmation of diagnosis
• Drug sensitivities.
• Molecular typing profile: “MIRUs”.
• “Fresh” samples / tissue: i.e. NOT formalin fixed as it kills the organism.

Question 22

How are sputum tests for TB given

Answer 22

3 “Early Morning” specimens.

Question 23

How can sputa be used for testing if there is a lack of it. What can be done to obtain some other form of aspirate.

Answer 23

– Induce sputa by nebulised saline- irritates patient and makes them cough.
– Bronchial aspirates
– Gastric aspirate- young children don’t cough up sputum they swallow it so wash lignin of intestine and send the sample.

Question 24

what is the composition of CSF be like in

Answer 24

– Protein will be high
– Glucose will be low
– Microscopy /culture

Question 25

Treatment for TB

Answer 25

• 2 months- Isoniazid, rifampicin, pyrazinamide ethambutol / (streptomycin)- all in one tablet
• 4 months- Isoniazid, rifampicin

Question 26

Treatment for meningitis induced by TB

Answer 26

corticosteroids

Question 27

Mantoux test

Answer 27

• Purified Protein derivative (MTB extract)- derived from TB and injected under the skin
• Cell mediated response
• Read @ 48-72 hours

Question 28

Interferon gamma release assays

Answer 28

•	Blood tests:
–	Immunological: 
•	Specific T-cells: IFN γ production.
–	TB specific antigens (ESAT6, CFP10)
•	DON’T cross-react with M bovis BCG.

Question 29

prevention of TB

Answer 29

BCG vaccine.

Question 30

2 clinical forms of leprosy

Answer 30

– Tuberculoid- immune system is dealing with it.
• Macules / plaques- skin leison
• Nerve: ulnar, common peroneal
– Lepromatous- immune system not dealing with it.
• Subcutaneous tissue accumulation.
• Ear lobes, face - leonine facies.

Question 31

treatment for TB

Answer 31

– Dapsone, rifampicin, clofazimine