Mycobacteria

Question 1

Name 2 important mycobacterial species

Answer 1

M. tuberculosis

M. leprae

Question 2

What proportion of the worlds popln has TB?

Answer 2

1/4-1/3 (ie 25% - 33%)

about 10% of these are having the active disease

Question 3

What is Pott’s disease?

Answer 3

TB of the vertebrae

Question 4

What are some of the features seen in leprosy?

Answer 4

lepromatous leprosy - patches seen on skin

leonine facies - due to loss of innervation, nose or fingers may fall off

Question 5

Are mycobacteria aerobic or anaerobic and what does this mean in terms of types of infections caused?

Answer 5

aerobic - mainly causes lung and skin infections

Question 6

What shape are mycobacteria?

Answer 6

bacilli

Question 7

What specific quality of the cell wall do mycobacteria have?

Answer 7

high molecular weight lipids

Question 8

What is special about mycobacteria and macrophages?

Answer 8

mycobacteria resist phagocytosis and can survive inside macrophages

Question 9

How fast do mycobacteria grow?

Answer 9

SLOWLY - doubling time 15-20hrs

Question 10

Why do mycobacteria take a long time to reproduce?

Answer 10

as their waxy membrane takes a lot of time and energy to form

Question 11

what are the key components of the lipid cell wall?

Answer 11

mycolic acids

lipoarabinomannan

Question 12

If mycobacteria grow slowly, what does that mean for the onset of the disease?

Answer 12

has a very slow and insiduous onset

Question 13

What difficulties in treatment does slow growth cause?

Answer 13

difficult to culture and so diagnosis may take a while - as the commensals would grow faster and completely overgrow the plate
treatment takes a long time, as bacteria are usually targeted for their growth and cell wall production

Question 14

What are Koch’s postulates?

Answer 14

infective diseases have these features:
Bacteria should be found in all people with disease.
Bacteria should be isolated from the infected lesions in people with the disease.
A pure culture inoculated into a susceptible person should produce symptoms of the disease.
The same bacteria should be isolated from the intentionally infected individual.

Question 15

What makes mycobacteria resistant to gram stain?

Answer 15

high lipid content of cell wall

Question 16

What stain is used for acid fast bacilli?

Answer 16

Ziehl-Neelsen stain

Question 17

What are the 3 steps to ZN staining?

Answer 17

carbol fuschin primary stain
acid alcohol (AFB - resistant to destaining)
methylene blue counterstain

Question 18

What is the name of the fluorescent stain used for AFB?

Answer 18

auramine phenol - is much more sensitive and easier to see the mycobacteria

Question 19

What is a common type of sample taken for TB?

Answer 19

sputum

Question 20

describe the ways to grow mycobacteria in culture

Answer 20

need to use antibiotics to prevent the growth of other bacteria
fastidious, so need special media such as Lowenstein Jensen (3-8 weeks)
can alternatively use liquid broth (1-3 weeks)
and then the mycobacteria are detected by MGIT

Question 21

What is culture followed up by?

Answer 21

speciation and testing for drug resistance

Question 22

Describe the nucleic acid detection of mycobacteria

Answer 22

PCR is used and is very sensitive

can even detect rifampicin resistance with fluorescence

Question 23

What die the Cd 4 T cell generate and how does this help in the immune response to mycobacteria?

Answer 23

interferon gamma

makes other macrophages more effective at killing mycobacteria

Question 24

What is a key histological feature of mycobacterial disease?

Answer 24

granuloma

Question 25

How long does it take for T cell responses to form against TB?

Answer 25

3-9 weeks

Question 26

What is the tuberculin skin test testing for?

Answer 26

memory T cells to TB

Question 27

What does the interferon gamma release assay involve?

Answer 27

using the white blood cells of the pt and exposing them to antigen from TB and seeing whether INF gamma is produced

Question 28

Why do we get different types of leprosy?

Answer 28

due to the immune response of the individual against leprosy - either a very large immune response that damages the tissues or to little immune response that the bacilli damage the tissues

Question 29

what difficulties are there in treating mycobacterial infections?

Answer 29

- slow replicating bacteria so need prolonged treatment - different poplns in different parts of the body - drug resistance so large combinations of drugs used - compliance is important

Question 30

What is the standard therapy for TB?

Answer 30

``` isoniazid + rifampicin + pyrazinamide + ethambutol for 2 months and then: rifampicin + isoniazid for the next 4 months ```

Question 31

give examples of drugs that may be used if there is resistance

Answer 31

streptomycin cycloserine capreomycin fluoroquinilones

Question 32

what side effects are there from anti-tuberculous drugs?

Answer 32

hepatotoxicity peripheral neuropathy optic neuritis

Question 33

What two factors of the apex of the lung make it favourable for the growth of TB?

Answer 33

more air | less blood supply (so less WBCs)

Question 34

Will anything abnormal be seen on X-ray with latent TB?

Answer 34

no

Question 35

IS latent TB detectable in a tuberculin prick test?

Answer 35

yes - as cell mediated response persists but the primary infection is contained

Question 36

What is the name given to TB that develops immediately following the primary disease?

Answer 36

post-primary infection

Question 37

What is a key feature of primary tuberculosis?

Answer 37

caseous necrosis resulting in cavities in the lung

Question 38

Where can TB spread to?

Answer 38

``` brain - meningitis all over - miliary TB bone and joint TB kidneys - genitourinary TB pleura - pleural TB TB peritonitis ```

Question 39

What type of T cell response is the the major immune response to TB?

Answer 39

Th1 which produce interferon gamma and TNF alpha

Question 40

Who is at increased risk of TB reactivation?

Answer 40

infants, young adults and elderly malnourished those with a high intensity of exposure the immunosuppressed