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Mycobacteriology Flashcards

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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
M. mucogenicum - Disease
Normal Host - sputum contaminant Immunocompromised Host - Catheter infections (well-documented) Lung infections? (unclear)
26
M. TB Complex - Species
``` M. tb M. bovis M. bovis BCG M. caprae M. africanum M. microti M. canetii M. pinnipedii ```
27
M. TB Complex orgs that are Niacin/Nitrate positive? And how are they distinguished?
MTB and M. canetii | MTB - rough, M. canetii - smooth
28
M. tb standard susceptibilities - drugs tested
``` SIRE + PZA Streptomycin (STR) Isoniazid (INH) Rifampin (RIF) Ethambutol (EMB) Pyrazinamide (PZA) ```
29
Which member of the TB complex is inherently resistant to Pyrazinamide (PZA)?
M. bovis
30
Definition of MDR TB
Resistant at least to both Isoniazid (INH) and Rifampin (RIF)
31
Definition of XDR TB
Additional resistance to any fluoroquinolone (the "floxacins") and resistant to at least one of the three injectable drugs for TB (capreomycin, amikacin, kanamycin).
32
M. avium Complex - Species
M. avium M. intracellulare M. chimaera "X cluster" - MAC probe pos, avium and intra. probe neg), includes M. colombiense, M. mantenii
33
M. avium Complex - Colony Morphology
Non-pigmented Smooth, flat, transparent colonies Rough variants can sometimes form
34
M. avium Complex - Disease
``` Frequently isolated slow growing NTM Chronic lung infections (CF, etc) Disseminated infections (usually AIDS pts) Lymphadenitis Cutaneous infections ```
35
M. xenopi - Colony Morphology
Classic "birds nest" colony morphology Enhanced growth at 42 deg. C Non-pigmented
36
M. xenopi - Disease and Treatment
Pulmonary infection Optimal treatment for M. xenopi infection is not well established - in vitro sensis do not correlate with clinical response
37
Where is M. xenopi commonly found?
Mat be found in hospital water taps, hot water storage tanks, and contaminated bronchoscopes
38
When do we perform sensis for MAC?
Only when treatment failure is suspected
39
M. kansasii - Colony Morphology
Photochromogen Flat, spready, dull colonies Initially off-white then becoming yellow with exposure to light
40
M. kansasii - Disease
Chronic respiratory infection Disseminated disease in AIDS Isolated from liver/spleen (hairy cell leukemia)
41
What Mycobacteria cross-react with a PPD?
M. kansasii
42
What Mycobacteria cross-react with a Quanterferon Gold (QFN)?
M. kansasii | M. marinum
43
M. kansasii - AST and observed resistance
Initially test for Rifampin - then others | Resistance observed to Ethanmbutol, Ciprofloxacin, Doxycyclin, and Capreomycin
44
M. marinum - Colony Morphology
Photochromogen Grows at 30 deg. C Irregular edged colonies, off-white turing bright yellow
45
M. marinum - Disease
"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
M. marinum - Susceptibility profile
``` Generally S to: Rifampin Rifabutin Etahmbutol Clarithromycin Trim/Sulfa ``` Generally R to: Isoniazid (INH) Pyrazinamide (PZA)
47
M. ulcerans - Colony Morphology and Culture
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
M. ulcerans - Disease
Ulcerative skin disease known as Buruli ulcer | most frequently seen in children in rural tropical environments near wetlands
49
M. gordonae - Colony Morphology
Scotochromogen | Orange, smooth, shiny colonies
50
M. gordonae - Disease
Not significant, ubiquitous in the environment
51
Which AFB do not grow in culture?
M. leprae M. tilburgii (rare species) M. genavense (grows in liquid media only)
52
Which AFB require special growth supplements?
M. haempohilum (hemin) | M. avium ssp paratuberculosis, M. genavensae (Mycobactin J - siderophore)
53
What are the cutoffs for positive PPD tests set by the CDC?
5mm - high risk (HIV+, exposure toe active TB pt) 10mm - increased probability (recent immigrants, IVDU, healthcare workers) 15 mm - low risk (everyone else)
54
What do DNA probes target?
The ribosomal RNA sequences (becuase have ~10,000 copies, provides natural amplification)
55
What Mycobacteria species have available probes?
M. TB complex (TB, bovis, africanum, etc) M. avium complex M. kansasii M. gordonae
56
How is DNA fingerprinting for epidemiology done in TB?
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
Mechanism of INH resistance?
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
Mechanism of Streptomycin resistance?
Mutations in rpsL gene (ribosomal S12 protein) and rrs (16s RNA)
59
Mechanism of RIF resistance?
Mutations in rpoB gene (B subunit of RNA polymerase)
60
Mechanism of fluoroquinolone resistance?
Mutations in gyrA (DNA gyrase)
61
What is preferred initial therapy for MAC?
Clarithromycin or Azithromycin PLUS ethambutol
62
What is the specimen of choice for TB diagnosis in kids?
Gastric aspirate, should be 5-10ml, same 3 consecutive day rule applies, neutralization recommended (1% sodium bicarb) for specimens >4 hrs from processing
63
Acceptable contamination rate for AFB processing?
3-5%
64
What can be added to specimens from CF patients for AFB work up?
5% oxalic acid added to conc sediments
65
What proteins are detected by IGRAs?
ESAT-6, CFP-10, and TB7.7
66
Which organisms can give false positive IGRA results?
M. marinum, M. kansasii, M. szulgai, M. flavescens
67
What are the types of leprosy and how do they differ clinically/diagnostically?
Lepromatous - many AFB in lesions (no CMI), biopsy nodules and plaques Tuberculoid - very few AFB, biopsy rims of lesions
68
What causes buruli ulcer? How is it cultured?
M. ulcerans, biopsy or swabs cultured for 6 weeks at 30 degrees
69
Which NTM can exhibit cording?
M. gordonae, M. chelonae, M. marinum
70
If isolate is Nicain positive - think?
M. tuberculosis
71
If isolate is Nicain positive and a photochromagen - think?
M. simiae
72
If isolate is R to pyrazinamide and a slow grower - think?
M. bovis of M. bovis BCG
73
If isolate is associated with pt with bladder cancer and intravesicular immunotherapy - think?
M. bovis BCG
74
What is critical concentration resistance?
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
Which RGM have an inducible erm gene?
M. fortuitum | M. abbscessus (subsp. absecssus and bolletti)
76
How do you test for inducible (erm) resistance in RGM?
Read Clarithromycin result at 3 days, then reincubate and read again at 14 days

Mycology & Mycobacteriology (2 decks)

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