Mycobacteria and TB

Question 1

Mycobacterium tuberculosis characteristics

Answer 1

Different to most other bacteria
Obligate aerobe - won’t grown in absence of O2
Live within macrophages - intracellular parasite
M. bovis in cattle

Question 2

TB can affect

Answer 2

Any system in the body
Most commonly affects the lungs
Can affect lymph nodes, bones, joints and kidneys

Question 3

Manifestions

Answer 3

Meningitis
Pot’s disease
Renal

Question 4

Transmission

Answer 4

Airborne
Spread in droplets
Frequent or close prolonged contact with an infected person is necessary

Question 5

Who is at risk

Answer 5

More likely to affect people whose immune system is weak

Question 6

At risk groups

Answer 6

HIV infections
Steroids, chemo, transplant 
Unhealthy, over-crowded conditions
Stay in high rate country 
Exposure to Tb in youth 
Malnourished

Question 7

Primary TB mech

Answer 7

Droplet nuclei inhaled
Taken up by alveolar macrophages
Droplet nuclei reach alveoli where infection starts
Granuloma in lung develops

Question 8

Granuloma in lung is called

Answer 8

Ghon focus

Question 9

Enlarged lymph nodes + GF makes

Answer 9

Primary complex

Organisms are walled off

Question 10

Secondary TB

When can it occur

Answer 10

Reactivation of dormant mycobacteria
Reinfection
Months, years and decades after primary infection
Most commonly occurs at apex of lungs where there is most oxygen

Question 11

Sequence of secondary tb

What happens to the airways

Answer 11

Caseous centres of tubercles liquefy
Organisms grown rapidly
Large load of antigens
- bronchi walls become necrotic and rupture
-cavity formation
-organisms spill into airways and spread
Primary lesions heal

Question 12

Infection vs disease

infection

Answer 12

Organism present 
skin test +ve 
radiograph normal 
sputum -ve 
no symptoms

Question 13

infection vs disease

disease

Answer 13

organism present
skin test +ve 
lesion on radiograph 
sputum +ve
symptoms 
infectious 
case of tb

Question 14

Most common symptoms

caused by cytokines

Answer 14

Persistent cough 
Anorexia
Weight loss
swollen glands
fever
night sweats
tiredness and being unwell 
coughing up blood

Question 15

Antibiotic treatment

Answer 15

Treat for 6 months
Use more than one to avoid resistance build up
Isoniazid, rifampicin, pyrazinamide and ethambutol-
prevent spread by isolating infectious patients

Question 16

Treatment

Answer 16

-ve pressure isolation 
vitamin D
ROLE IN  ACTIVATING MACROPHAGES
non-infectious after 2 weeks 
must ct for 6months+

Question 17

Fatality rates

Answer 17

Untreated

Treated

Question 18

BCG vaccine

Answer 18

Restricted to vaccine

No impact on HIV related TB

Question 19

TB + HIV/AIDS

Answer 19

HIV makes TB worse
Increases risk of acquiring it
TB treatment slows down HIV

Question 20

Extensive drug resistance

MDRTB

XDR TB

Risk factors

Answer 20

Multi-drug resistance TB

Extensively drug resistant TB

Previous treatment, contact with MDRTB, HIV+, London resident

Question 21

TB in animals e.g cattle

Answer 21

Myco. Bovis
Pasteurisation solves this problem
Increase in TB in cattle over last decade - spread by badgers?

Question 22

Obstacles to TB control

Answer 22

Lack of financial resources
Social instability 
HIV epidemic - doubles TB death rate
Drug resistance 
Stigma

Question 23

Diagnosis of TB

Answer 23

Radiograph - indicates but does not confirm
Skin test - inject organism and look for signs of inflammatory reaction - tuberculin ascertains infection not disease

T-spot - detect reactive T cells, not BCG

Question 24

Microscopy

Answer 24

Staining - ziehl neelsen
- needs >10000 organisms/ml
Fluorescent staining

Question 25

Culture

Answer 25

Sputum extracted

NaOH applied kills all bacteria except mycobacteria

Question 26

Automatic culture

Answer 26

Mycobacterium use O2, lifts the quenching and causes fluorescent section

Question 27

Nucleic acid detection test

Answer 27

PCR assay