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Respiratory Diseases & Dermatology > PT1: Tuberculosis Pathophysiology, Microbiology and Treatment > Flashcards

PT1: Tuberculosis Pathophysiology, Microbiology and Treatment Flashcards

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1
Q

what bacteria causes TB

A

mycobacterium tuberculosis

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2
Q

what type of bacteria is mycobacterium tuberculosis

A

slow growing bacillus

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3
Q

what part of the body does mycobacterium tuberculosis infect

A

lungs (pulmonary TB)

can spread to other organs

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4
Q

what are the features of acid fast bacteria

A

cell wall is lipid rich

very hydrophobic, resistant to drying and weak disinfectants

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5
Q

what are the three types of mycobacterium tuberculosis

A

m. bovis, m. africanum, m. microti

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6
Q

which form of mycobacterium tuberculosis is not pathogenic

A

m. microti

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7
Q

what types of mycobacterium tuberculosis do not cause disease in immunocompetent people

A

m. bovis, m. africanum

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8
Q

what occurs in stage 1 progression of primary tuberculosis

A

bacilli inhaled in droplets, settle in alveoli in lung, start to grow
phagocytosed by macrophages which do not destroy bacilli, so it can survive outside the host

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9
Q

how many organisms are needed to cause infection in primary tuberculosis

A

<10 organisms

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10
Q

what occurs in stage 2 progression of primary tuberculosis

A

mycobacterium tuberculosis multiplies inside macrophages for 7-21 days
macrophages burst, incoming macrophages phagocytose released MTB
continues for 3-4 weeks
asymptomatic or mild fever

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11
Q

what happens in stage 3 of progression of primary tuberculosis

A

cell mediated response initiated, granulomas (tubercules) formed, symptoms appear

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12
Q

what percentage of tuberculosis progresses to latent infection

A

45-50%

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13
Q

what percentage of tuberculosis progresses to progressive infection

A

5-10%

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14
Q

what percentage of tubercolosis infections are cleared

A

45-50%

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15
Q

what occurs during stage 4 of tuberculosis progression

A

bacteria multiply inside macrophage; uncontrolled lysis means bacteria spread throughout the lungs
enzymes released destroy local tissue causing legions in the lung (pulmonary TB)

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16
Q

what are the symptoms of TB (appearing at stage 4)

A

cough, afternoon fever, weight loss, blood stained sputum, night sweats

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17
Q

how is active TB diagnosed

A

clinical examination, chest x-ray, sputum test (smears/cultures), molecular assays

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18
Q

what is the appearance of a chest x-ray for active TB

A

white lesions replace alveoli with scar tissue

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19
Q

what is the appearance of a sputum test for active TB

A

visualise bacteria in sputum using staining/microscopy, culture bacteria

20
Q

what is the appearance of molecular assays for active TB

A

Xpert MTB/RIF assay

21
Q

what are the methods of latent TB diagnosis

A

tuberculin skin test (Mantoux test), molecular tests (interferon-gamma assay)

22
Q

how does a tuberculin skin test work

A

tuberculin injected subcutaneously into forearm

positive test is skin lesion >10mm diameter after 48-72 hours

23
Q

how is TB screened for

A

chest x-ray, sputum test

24
Q

when is TB screening compulsory

A

for people travelling to a country where TB is common if they are staying in the UK for >6 months
needed before visa applications

25
Q

what vaccine is used to prevent TB

A

BCG (bacillus calmette-guerin) vaccine

26
Q

what are some examples of 1st line anti-TB drugs

A

rifampicin, isoniazid, pyrazinamide, ethambutol

27
Q

how does rifampicin work

A

inhibits RNA polymerase, bactericidal to all metabolising cells, oral, fully absorbed
absorption decreased by food

28
Q

what are the side effects of rifampicin

A

liver damage, hypersensitivity, decreased activity of other drugs, red colour in body fluids

29
Q

how does isoniazid work

A

prodrug - bactericidal to actively growing bacilli; bacteriostatic to very slow growing bacilli
decreases synthesis of mycolic acid

30
Q

what are the pharmcokinetics of isoniazid

A

oral absorption can be reduced by cations; well distributed including CSF; metabolised in liver and excreted in kidneys

31
Q

what are the side effects of isoniazid

A

hypersensitivity, peripheral neuropathy, liver toxicity, decreased efficacy of hormonal birth control

32
Q

how does pyrazinamide work

A

prodrug - bactericidal to dormant bacilli; decreases synthesis of mycolic acid and damages bacterial membrane

33
Q

what are the pharmacokinetics of pyrazinamide

A

well absorbed orally, good distribution including CSF, metabolised by liver and excreted by kidenys

34
Q

what are the side effects of pyrazinamide

A

joint pain, liver damage, hypersensitivity

35
Q

how does ethambutol work

A

bacteriostatic against actively growing bacilli; increases permeability by affecting synthesis of arabinogalactan in cell wall

36
Q

what are the pharmacokinetics of ethambutol

A

well absrbed orally and well distributed; 50% excreted unchanged in urine

37
Q

what are the side effects of ethambutol

A

optic neuritis (reversible), joint pain

38
Q

what is the site of action for isoniazid

A

inhibits cell wall formation and only kills dividing bacilli

39
Q

what is the site of action of ethambutol

A

bacteriostatic against actively growing TB bacilli

40
Q

what is the site of action for pyrazinamide

A

damages/kills slowly metabolising and dormant bacilli

41
Q

what is the site of action of rifampicin

A

kills all metabolising cells including some that are not dividing

42
Q

how is active TB treated

A

rifampicin & isoniazid for 6-9 months

pyrazinamide & ethambutol for first two months

43
Q

how is latent TB treated

A

specific patient groups are treated

isoniazid (6 months) or rifampicin & isoniazid (3 months)

44
Q

what are some examples of 2nd line anti-TB drugs

A 
streptomycin (aminoglycoside)
capreomycin (aminoglycoside)
cycloserine (neurological side effects)
ciprofloxacin (quinolone)
azithromycin (newer macrolide)
linezolid (oxazolidinone)
bedaquiline (dairy quinolone)
45
Q

how does TB drug resistance occur

A

results from poorly managed TB care, resistance through high rate of spontaneous mutations in drug target sites and efflux

46
Q

what are MDR-TB drugs

A

strains resistant to >2 first line drugs

47
Q

what are XDR-TB drugs

A

strains resistant to >2 first line drugs and >3 of the six second line drugs

Respiratory Diseases & Dermatology (34 decks)

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