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Mycology & Mycobacteriology > Mycobacteriology > Flashcards

Mycobacteriology Flashcards

1
Q

What bacterial killing agent is used for processing AFB samples?

A

Sodium hydroxide (NaOH)

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2
Q

What mucolytic agent is used for processing AFB samples?

A

N-acetyl-L-cysteine (NALC)

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3
Q

What is the classic smear and culture presentation for TB?

A

Smear positive

Culture negative

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4
Q

What is the sensitivity of AFB smears?

A

5,000 - 10,000 AFB/mL sputum

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5
Q

In what media does cording occur?

A

Liquid (MIGT)

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6
Q

Important things to remember about cording?

A

Not all TB cord, and not all cording is TB

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7
Q

What specimens get direct SecA1 sequencing?

A

All first time smear positive patients

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8
Q

What stain for AFB is used for direct patient samples?

A

Auramine rhodamine (AR)

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9
Q

What stain for AFB is used from media (solid or liquid)?

A

Kinyon

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10
Q

Which orgs may be Kinyon negative? Why? What do we do for confirmation?

A

Rapid growers
Have less mycolic acid in cell wall (less developed)
Modified acid-fast stain

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11
Q

How do we differentiate TB from m. bovis?

A

PCR

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12
Q

What are initial steps in identification of Mycobacteria?

A 
Growth rate (fast 7 days)
Colony morphology (not rough, slow growing - rule out TB)
Color (non-pigmented, photo, scoto)
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13
Q

Mycobacteria - Rapid Growers

A

M. abscessus
M. chelonae
M. fortuitum

M. mucogenicum
M. smegmatis

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14
Q

Mycobacteria - Slow Growers

A 
M. TB complex (tuberculosis, bovis, BCG, etc.)
M. avium
M. intracellulare
M. haemophilum
M. genavense
M. kansasii
M. marinum
M. xenpoi
M. gordonae
M. scrofulaceum
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15
Q

Mycobacteria - Photochromogens

A

M. kansasii
M. marinum
M. asiaticum
M. simiae

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16
Q

Mycobacteria - Scotochromogens

A

M. scrofulaceum
M. gordonae
M. szuldai
M. flavescens

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17
Q

M. fortuitum - Colony Morphology

A

Rapid grower
Smooth (or rough), shiny
Irregular edge

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18
Q

M. fortuitum - Disease

A

Localized traumatic wound infections
Catheter infections
Surgical/Cosmetic surgery wound infections (breast augmentation)
Rarely a respiratory pathogen

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19
Q

M. abscessus group - Species

A

M. abscessus
M. massiliense
M. bolletii

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20
Q

M. abscessus group - Colony Morphology

A

Rapid grower

??

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21
Q

M. abscessus group - Disease

A

Chronic lung infections (CF, CGD patients)
Localized traumatic would infections
Surgical infections
Disseminated skin infections (pts on corticosteroids, organ transplants)
Catheter infections
Eye infections

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22
Q

M. chelonae - Colony Morphology

A

Rapid grower

??

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23
Q

M. chelonae - Disease

A

Localized traumatic wound infections
Post-traumatic or post-surgical corneal infections
Catheter infections
Disseminated skin infections (pts on corticosteroids, organ transplants)
Sinusitis

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24
Q

M. mucogenicum - Colony Morphology

A

Off white, mucoid, shiny, smooth?

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25
Q

M. mucogenicum - Disease

A

Normal Host - sputum contaminant
Immunocompromised Host -
Catheter infections (well-documented)
Lung infections? (unclear)

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26
Q

M. TB Complex - Species

A 
M. tb
M. bovis
M. bovis BCG
M. caprae
M. africanum
M. microti
M. canetii
M. pinnipedii
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27
Q

M. TB Complex orgs that are Niacin/Nitrate positive? And how are they distinguished?

A

MTB and M. canetii

MTB - rough, M. canetii - smooth

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28
Q

M. tb standard susceptibilities - drugs tested

A 
SIRE + PZA
Streptomycin (STR)
Isoniazid (INH)
Rifampin (RIF)
Ethambutol (EMB)
Pyrazinamide (PZA)
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29
Q

Which member of the TB complex is inherently resistant to Pyrazinamide (PZA)?

A

M. bovis

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30
Q

Definition of MDR TB

A

Resistant at least to both Isoniazid (INH) and Rifampin (RIF)

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31
Q

Definition of XDR TB

A

Additional resistance to any fluoroquinolone (the “floxacins”) and resistant to at least one of the three injectable drugs for TB (capreomycin, amikacin, kanamycin).

32
Q

M. avium Complex - Species

A

M. avium
M. intracellulare
M. chimaera
“X cluster” - MAC probe pos, avium and intra. probe neg), includes M. colombiense, M. mantenii

33
Q

M. avium Complex - Colony Morphology

A

Non-pigmented
Smooth, flat, transparent colonies
Rough variants can sometimes form

34
Q

M. avium Complex - Disease

A 
Frequently isolated slow growing NTM
Chronic lung infections (CF, etc)
Disseminated infections (usually AIDS pts)
Lymphadenitis
Cutaneous infections
35
Q

M. xenopi - Colony Morphology

A

Classic “birds nest” colony morphology
Enhanced growth at 42 deg. C
Non-pigmented

36
Q

M. xenopi - Disease and Treatment

A

Pulmonary infection
Optimal treatment for M. xenopi infection is not well established - in vitro sensis do not correlate with clinical response

37
Q

Where is M. xenopi commonly found?

A

Mat be found in hospital water taps, hot water storage tanks, and contaminated bronchoscopes

38
Q

When do we perform sensis for MAC?

A

Only when treatment failure is suspected

39
Q

M. kansasii - Colony Morphology

A

Photochromogen
Flat, spready, dull colonies
Initially off-white then becoming yellow with exposure to light

40
Q

M. kansasii - Disease

A

Chronic respiratory infection
Disseminated disease in AIDS
Isolated from liver/spleen (hairy cell leukemia)

41
Q

What Mycobacteria cross-react with a PPD?

A

M. kansasii

42
Q

What Mycobacteria cross-react with a Quanterferon Gold (QFN)?

A

M. kansasii

M. marinum

43
Q

M. kansasii - AST and observed resistance

A

Initially test for Rifampin - then others

Resistance observed to Ethanmbutol, Ciprofloxacin, Doxycyclin, and Capreomycin

44
Q

M. marinum - Colony Morphology

A

Photochromogen
Grows at 30 deg. C
Irregular edged colonies, off-white turing bright yellow

45
Q

M. marinum - Disease

A

“Swimming pool” or “fish tank granuloma”

Is found in fresh and salt water, diagnosis often delayed due to uncommon org and failure to recall aquatic exposure

46
Q

M. marinum - Susceptibility profile

A 
Generally S to:
  Rifampin
  Rifabutin
  Etahmbutol
  Clarithromycin
  Trim/Sulfa

Generally R to:
Isoniazid (INH)
Pyrazinamide (PZA)

47
Q

M. ulcerans - Colony Morphology and Culture

A

Extremely slow growing (6-12 wk inc. at 32 deg. C)
Colonies are yellowish, rough, with well-demarcated edges
Culture fails in over half of cases, is confirmed by molecular methods

48
Q

M. ulcerans - Disease

A

Ulcerative skin disease known as Buruli ulcer

most frequently seen in children in rural tropical environments near wetlands

49
Q

M. gordonae - Colony Morphology

A

Scotochromogen

Orange, smooth, shiny colonies

50
Q

M. gordonae - Disease

A

Not significant, ubiquitous in the environment

51
Q

Which AFB do not grow in culture?

A

M. leprae
M. tilburgii (rare species)
M. genavense (grows in liquid media only)

52
Q

Which AFB require special growth supplements?

A

M. haempohilum (hemin)

M. avium ssp paratuberculosis, M. genavensae (Mycobactin J - siderophore)

53
Q

What are the cutoffs for positive PPD tests set by the CDC?

A

5mm - high risk (HIV+, exposure toe active TB pt)
10mm - increased probability (recent immigrants, IVDU, healthcare workers)
15 mm - low risk (everyone else)

54
Q

What do DNA probes target?

A

The ribosomal RNA sequences (becuase have ~10,000 copies, provides natural amplification)

55
Q

What Mycobacteria species have available probes?

A

M. TB complex (TB, bovis, africanum, etc)
M. avium complex
M. kansasii
M. gordonae

56
Q

How is DNA fingerprinting for epidemiology done in TB?

A

Restriction fragment length polymorphism
DNA is fragment using a restriction endonuclease, run on a gel, and then probed for IS6110 (has many copies inserted throughout genome)

57
Q

Mechanism of INH resistance?

A

Deletion/mutation in katG gene, isolates become catalase negative or have decreased catalase activity
Resistance also associated with changes in inhA gene encoding for an enzyme in mycolic acid synthesis

58
Q

Mechanism of Streptomycin resistance?

A

Mutations in rpsL gene (ribosomal S12 protein) and rrs (16s RNA)

59
Q

Mechanism of RIF resistance?

A

Mutations in rpoB gene (B subunit of RNA polymerase)

60
Q

Mechanism of fluoroquinolone resistance?

A

Mutations in gyrA (DNA gyrase)

61
Q

What is preferred initial therapy for MAC?

A

Clarithromycin or Azithromycin PLUS ethambutol

62
Q

What is the specimen of choice for TB diagnosis in kids?

A

Gastric aspirate, should be 5-10ml, same 3 consecutive day rule applies, neutralization recommended (1% sodium bicarb) for specimens >4 hrs from processing

63
Q

Acceptable contamination rate for AFB processing?

A

3-5%

64
Q

What can be added to specimens from CF patients for AFB work up?

A

5% oxalic acid added to conc sediments

65
Q

What proteins are detected by IGRAs?

A

ESAT-6, CFP-10, and TB7.7

66
Q

Which organisms can give false positive IGRA results?

A

M. marinum, M. kansasii, M. szulgai, M. flavescens

67
Q

What are the types of leprosy and how do they differ clinically/diagnostically?

A

Lepromatous - many AFB in lesions (no CMI), biopsy nodules and plaques
Tuberculoid - very few AFB, biopsy rims of lesions

68
Q

What causes buruli ulcer? How is it cultured?

A

M. ulcerans, biopsy or swabs cultured for 6 weeks at 30 degrees

69
Q

Which NTM can exhibit cording?

A

M. gordonae, M. chelonae, M. marinum

70
Q

If isolate is Nicain positive - think?

A

M. tuberculosis

71
Q

If isolate is Nicain positive and a photochromagen - think?

A

M. simiae

72
Q

If isolate is R to pyrazinamide and a slow grower - think?

A

M. bovis of M. bovis BCG

73
Q

If isolate is associated with pt with bladder cancer and intravesicular immunotherapy - think?

A

M. bovis BCG

74
Q

What is critical concentration resistance?

A

Growth of >1% of the inoculum in a the presence of the concentration of the drug that is the lowest conc that is 95% of “wild” strains

75
Q

Which RGM have an inducible erm gene?

A

M. fortuitum

M. abbscessus (subsp. absecssus and bolletti)

76
Q

How do you test for inducible (erm) resistance in RGM?

A

Read Clarithromycin result at 3 days, then reincubate and read again at 14 days

Mycology & Mycobacteriology (2 decks)

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