W05_04 Mycobacteria

Question 1

what is an m.tuberculosis complex?

Answer 1

a group of mycobacteria spp. that cause similar symptoms of tuberculosis. m. tuberculosis and m. bovis are most common

Question 2

microbiology of mycobacteria?

Answer 2

non-gram staining;
aerobes;
don't form spores;
non-motile;
10,000 cells/mL needed to see with light microscopy

Question 3

which stains do we use for mycobacteria?

Answer 3

acid-fast stain (ziehl-nielesen or kinyoun);

fluorochrome dyes are more sensitive

Question 4

how long does it take for mycobacteria to grow?

Answer 4

15-20 hours

Question 5

non-tuberculous myco. are divided between slowly growing (>7d) and rapidly growing (~7d) and intermediate (7-10d)

Answer 5

okay.

Question 6

can you culture m.leprae in vitro?

Answer 6

no.

Question 7

what’s the gold standard for identifying mycobacteria?

Answer 7

culture.

nucleic acid amplification is an alternative for the ribosomal RNA/DNA

Question 8

what’s the reservoir for mtb complex and m.leprae?

Answer 8

warm blooded animals;

in contrast, NTM are usually environmental, free-living, and usually around water

Question 9

what percentage of reported TB in canada is by foreign born individuals?

Answer 9

66%

Question 10

where is the primary focus of tuberculosis?

Answer 10

middle and lower lung zones

Question 11

where is the secondary focus of tuberculosis?

Answer 11

upper lungs, lymph nodes, vertebral bodies, meninges

Question 12

what’s the ghon complex?

Answer 12

granuloma PLUS an active lymph node (see two bright spots on CXR)

Question 13

how many people become latent TB carriers after infection?

Answer 13

95%; 5% will go to actually get the disease

Question 14

what’s miliary TB?

Answer 14

when the bacteria enter circulation and spread throughout the body, causing lesions everywhere

Question 15

know latent vs. active TB

Answer 15

okay.

Question 16

how do monocytes respond to the TB infection?

Answer 16

get activated with TNFa and prevent the intracellular replication of Mtb;
macrophages produce IL-1, TNFalpha

Question 17

how do Th1 cells respond to TB? (cytokines?)

Answer 17

these CD4+ cells respond with IL-2, IFNy, IL-12 (all inflammatory)

Question 18

what’s the mantoux test?

Answer 18

tuberculin skin test, using purified protein derivative 5 TU.

Question 19

a positive TB skin test is defined by how big of a bump

Answer 19

> 10mm diameter.

>5 mm diameter in certain risk groups

Question 20

false negatives: active TB, immunocompromised

Answer 20

false positives: other mycobacteria, BCG vaccine

Question 21

how does the interferon gamma release assay (IGRA) work?

Answer 21

blood drawn and t cells exposed to Mtb. IFNy measured.

Question 22

management of active TB?

Answer 22

2 or more drugs: isoniazid, rifampin, pyrazinamide, ethambutol

Question 23

management of latent TB?

Answer 23

isoniazid for 9 months

Question 24

note: BCG does NOT protect against infection.

Answer 24

it only prevents clinical disease and dissemination

Question 25

what’s another name for hansen’s disease?

Answer 25

leprosy

Question 26

how is m.leprae transmitted?

Answer 26

we don’t know; likely airborne, not contact

Question 27

what’s the pathogenesis of m.leprae?

Answer 27

infects and multiplies in macrophages. they can resist oxidative killing by their surface phenolic glycolipid

Question 28

what are the two extremes of leprosy?

Answer 28

tuberculoid,

lepromatous

Question 29

what are clinical features of tuberculoid leprosy?

Answer 29

red blotchy lesions;
localized anaesthesia;
thickening of nerve sheaths;

Question 30

what are clinical features of lepromatous leprosy?

Answer 30

local anesthesia causing secondary infections leading to disfigurement

Question 31

reservoir for m. avium complex?

Answer 31

environment and birds

Question 32

main disease of m. avium complex?

Answer 32

TB or disseminated in AIDS patients