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T IoD medical micrcobiology > Tuberculosis > Flashcards

Tuberculosis Flashcards

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USMLE® Step 1 flashcards
1
Q

what atypical bacterias cause TB?

A

M.kansasii
M.chelonae
M.A.I; mycobacterium avium intercellulare group

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2
Q

what bacteria are part of the M.T.B group?

A

M.tuberculosis
M.bovis
BCG
M.africanum

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3
Q

what is the vague structure of TB mycobacteria?

A

they have a thick cell wall and mycolic acid

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4
Q

mycobacterium is acid fast, what stains can be used?

A
  1. ziehl-neelsen

2. auramine

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5
Q

how does the ziehl neelsen stain work?

A

Its added, heated and then stains the organism red

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6
Q

how does the auramine stain show TB?

A

it fluoresces and is used more in practice

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7
Q

how do you culture mycobacteria in a solid medium?

A

In a Lowenstein Jensen medium

slow process at 3-6 weeks and need a lot of bacteria in the sample

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8
Q

what is mycobacteria culture moving towards a liquid medium?

A

It’s much faster so can be done in days instead of weeks

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9
Q

what are the advantages of using PCR for TB?

A

rapid
specific
resistance information

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10
Q

what is the disadvantage of using PCR for TB?

A

not as sensitive as culture

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11
Q

what populations are at risk of TB?

A 
immigrants
elderly
immunosuppressed; HIV, Lymphoma, long term steroids or chemo
diabetic
alcoholic
homeless
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12
Q

what is the transmission of TB?

A

Droplet
direct contamination
infectivity related to sputum smear positivity.

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13
Q

what is the time cut off for contact tracing?

A

spending 8 hours with the patient

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14
Q

what is the course of primary infection of TB?

A
  • the nuclei is inhaled into the mid lung zone
  • the nuclei is ingested by alveolar macrophages
  • the infected macrophages spread to the lymphatics
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15
Q

what can primary infection progress to?

A

pneumonia, spread, meningitis, rupture into pleural space

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16
Q

why can TB progress to active infection?

A

Stress, poor health, malnutrition, malignancy, immunosupresion, surgery

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17
Q

what is seen histologically in pulmonary TB?

A

caeseous necrosis, granulomas, fibrosis, cavities in lung apex

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18
Q

what is the clinical presentation of TB?

A

history of cough, weight loss, fever.

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19
Q

what is tuberculous meningitis?

A

extrapulmonary TB of the CNS

rupture of the tubercle into sub arachnoid space.

20
Q

what is a common example of skeletal TB?

A

spine Potts disease

21
Q

what is the RIPE treatment for TB?

A

R rifampicin
I isoniazid
P pyrazinamide
E ethambutol

22
Q

Other than RIPE what are some other first line medications that can be given?

A

streptomycin

fluoroquinolone

23
Q

what are 2nd line treatments for TB?

A

ethionamide
Cycloserine
Capreomycin

24
Q

what are third line treatments for TB?

A

clarithromycin

Co-amoxiclav

25
Q

what is the RIPE regime?

A

RIPE given for initial 2 months

rifampicin and isoniazid given for a further four months

26
Q

what is the RIPE regime for CNS TB?

A

RIPE for initial 2 months

rifampicin, isoniazid and steroids for a further 10 months

27
Q

what are some adverse reactions of rifampicin?

A

hepatitis
rash
GI upset
drug interaction with prednisolone

28
Q

what are some adverse reactions of isoniazid?

A

rash
peripheral neuropathy
hepatitis

29
Q

what are some adverse effects of ethambutol?

A

dose related optic neuropathy

30
Q

what are some adverse effects of pyrazinamide?

A 
hepatitis
facial flush
rash
nausea
high uric acid
31
Q

what are the expectations of treatment?

A

non infectious within 2 weeks

1 month will gain weight and have a negative sputum smear

32
Q

if it’s MDR TB what does this mean?

A

its resistant to isoniazid and rifampicin

33
Q

if it’s XDR TB what does this mean?

A

resistant to isoniazid and rifampicin plus any fluroquinolone and at least one of the three infectable second line drugs (amikacin, kanamycin, capreomycin)

34
Q

what type of test is the tuberculin skin test?

A

A delayed type IV hypersensitivity reaction

35
Q

how long does the tuberculin skin test take?

A
  • 12 hours you get interdigitating dendritic cells
  • 24-48 hours large numbers of activated macrophages
    in 48 hours; primed T cells
36
Q

what does the skin test measure?

A

the induration and erythema

37
Q

what does the blood test measure?

A

IFN gamma production

38
Q

explain the administration of the mantoux test?

A

0.1ml of 2TU staten serum institute PPD intra-dermally

wait 48-72 hours after it had been administered

39
Q

how do you interpret a mantoux test?

A

<5mm is negative

>15mm is likely to be TB

40
Q

what is interferon gamma release assay?

A

a new test for diagnosing TB
in a test tube. lymphocytes are primed if there has been previous TB exposure so the interferon will be released faster,
measuring the time period for gamma interferon to be produced

41
Q

what is special about the mycobacterium cell wall?

A

Coated in a thick mycolic acid layer causing higher resistance

42
Q

what is the gram staining on mycobacteria?

A

Due to the mycolic acid cell membrane it resists gamma staining

43
Q

how do you explain the granuloma you see in pulmonary TB?

A

a centre of macrophages which are infected (these will become necrosed), ssurrounded by lymphocytes. surrounded by T cells

44
Q

what is the caseous necrosis seen in pulmonary TB?

A

in the centre of the previous granuloma. it’s previous bacteria and macrophages.

45
Q

in TB what is the ghon complex?

A

a calcified granuloma seen after primary TB.

46
Q

where is secondary TB found?

A

upper lobes

47
Q

what can be seen in a TB chest Xray?

A

Ghon complex
calcification
nodules

T IoD medical micrcobiology (4 decks)

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