FRCpath microbiology part 2 > Mycobacterium > Flashcards

Mycobacterium Flashcards

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1
Q

What bacteria belong to Mycobacterium
tuberculosis complex ?

A

1-M. tuberculosis
2-M. bovis,
3-M. africanum
4-M.microti

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2
Q

What is the BCG vaccine content?

A

Live attenuated strain from M. Bovis

#Contains Danish strain 1331

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3
Q

What is the generation time of MTB?

A

15-20 hours
(Extremely slow-growing )

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4
Q

What are the growth requirement of MTB ?

A
  • Strictly aerobic
  • Enhanced growth with 5-10% CO₂
  • Extreme slow-growers (GT:15-20 h)
  • Requires 3-8 weeks for visible growth on solid media
  • Optimal Temp 35-37°C
  • Optimum PH 6.4-7.0
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5
Q

Name 2 solid media can be used to grow MTB ?

A
  • Löwenstein-Jensen medium
  • Middlebrook 7H10 & 7H11 transparent agars
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6
Q

What are the 3 commonest liquid MTB media ?

A
  • Middlebrook 7H9 broth
  • BACTEC MGIT 960 (Mycobacteria Growth Indicator Tube)
  • BD BACTEC™
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7
Q

What are the virulance factors of MTB?

A

1-Cell wall resist degradation
2-Can survive within macrophages
3- Biofilms formation
4-Enzymatic degradation of reactive oxygen spp.

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8
Q

What are the definitions of TB exposure?

A

1- Household
2-Contacts with a cumulative exposure ≥ 8 h in a restricted area

3- Contacts ≥ 4 h for vulnerable in a restricted area:
#Children < 5 y #Immunocompromised

4-Exposure in medical procedures (e.g. bronchoscopy, sputum induction or autopsy)

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9
Q

Where is the commonest site of pulmonary TB reactivation?

A

Upper lobe

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10
Q

What is the commonest site of TB lesion in 1ry infection?

A

Middle and lower lobe

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11
Q

Mycobacterium lab ID (Microscopy)?

A
  • Non-motile/ Non-sporing
  • Weakly Gram-positive Bacilli
  • About 1-4 μm in length and 0.3-0.6 μm in width
  • Strongly acid-fast
  • Characteristic “cord formation”
  • Strictly aerobic
  • Extremely slow-growing
  • Rough, dry, wrinkled (breadcrumb-like)
  • Buff/cream-colored & non-pigmented colonie
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12
Q

What is the best staining ctypes of MTB?

A

They are Strongly acid-fast using:

1-Ziehl-Neelsen (ZN) stain:
bright red with blue background
2-Auramine-rhodamine:
bright yellow-green fluorescent

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13
Q

What is the Lowenstein Jensen medium?

A
  • Egg-based medium
  • ## Appears as a pale green slant due to malachite green
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14
Q

What is the BACTEC MGIT 960 ?

A
  • Mycobacteria Growth Indicator Tube
  • Liquid Media
  • Uses oxygen-sensitive fluorescent detection
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15
Q

Lab ID MTB (Growth featues)?

A
  • Strictly aerobic
  • Extremely slow-growing
  • 35-37°C
  • Enhanced with 5-10% CO₂
  • pH of 6.4-7.0
  • Rough, dry, wrinkled (“breadcrumb-like”)
  • Buff/cream-colored
  • “Cord factor” appearance when colonies viewed microscopically
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16
Q

Lab ID MTB biochemical tests?

A
  • Catalase: Weakly positive
  • Niacin accumulation: Positive
  • Nitrate reduction: Positive
  • Pyrazinamidase: Positive
  • Urease: Usually positive
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17
Q

What are teh available test for LTBI?

A

1- tuberculin skin test (TST) :
2-interferon-gamma release assays (IGRAs) :
- QuantiFERON-TB Gold In Tube® (QFT, Cellestis)
- T-Spot.TB® (Oxford Immunotec)

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18
Q

T/F:
IGRA can be used in diagnosing MTB infection?

A

No
only in LTNI

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19
Q

What is the principle of IGRA test?

A
  • Detect the release of IFN-γ
  • Which is produced in response to ESAT-6 & CFP-10
  • These antigens are unique to MTB (not in BCG or NTMs)
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20
Q

What are the diffrences between Tspot TB and GFT IGRA?

A

1-QFT
- Quantitative test
- ELISA based test
- Measur interferon-gamma secreted from T-lymphocytes
——-@

2-T-Spot-TB:
- Immunospot assay
- Direct count of sensitised T-effector cells.
- It measures the number of IFN-gamma-producing cells (spots)

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21
Q

What are the advantages of IGRA test?

A

1-Requires a single patient visit
2-Prior BCG vaccination does not cause a false-positive IGRA test result.

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22
Q

Disadvantages of IGRA test?

A
  • Cannot distinguish latent TB from active TB
    ————————–@
  • No prognostic value
    ————————-@
  • Limited data for:
    Children younger than 5 Immunocompromised
    Recently exposed to MTB
    Serial testing
    ————————–@
  • Requires proper sample handling
    ————————-@
  • Expensive
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23
Q

What is the lab requirement ti process IGRA test?

A

Blood samples must be processed within 8-30 hours after collection (when WBC are still viable)

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24
Q

What are the causes of Indeterminate IGRA test?

A

Indicates a test failure due to:
1- Insufficient IFN-γ due to T-cell dysfunction
2- Possible technical issues or laboratory error.

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25
What are the NTM that can give positive IGRA test ?
M. kansasii M. marinum M. szulgai
26
What are the spp belong to M. abscessus complex ?
- M. abscessus - M. massiliense - M. bolletii
27
Whic NTM are in Runyon Group 2 Scotochromogenic (Slow growers)?
- M. scrofulaceum - M. gordonae - M szulgai - M xenopi
28
What are the Scotochromogens NTMs?
- It is Group II Runyon - Produce pigment in both light and dark
29
What are the Nonchromogenic NTM?
- Group III Runyon - Do not produce any pigment regardless of light exposure - This group includes MAC, M. ulcerans ,M terrae complex
30
Photochromogens Runyon NTM group?
- Group I - Produce pigment only when exposed to light - A classic example is Mycobacterium kansasii.
31
What are the rapid grower NTMs?
- M. fortuitum - M. abscessus complex - M chelonae
32
What is teh cause of Buruli ulcer?
M ulcerans
33
Whis NTM can cause human to human transmission?
- M massilense - M abscessus in CF
34
What are the NTM that can cause dissaminated infection in HIV?
- M. abscessus - M. chelonae - M kansasii
35
Expaline why M kansasii can give +ve IGRA test?
because it can produce CFP-10 and ESAT-6 antigens
36
Causative agent of fish tank granuloma?
M marinum
37
T/F: M. marinum grows best at 31°C, in contrast to other mycobacteria.
T other mycobacteria best grow at 37
38
What is the empiricat Tx if M marinum is suspected
- Clarithromycin - Once diagnosis confirmed , add a 2nd agent: ethambutol or rifampin - Duration: 1–2 months after resolution ideally 3-4 months total
39
What are the virulance factors of M abscessus?
- Biofilm formation - Smooth>Rough morphotypes - Enzymes (esterases, proteases & functional type VII secretion system (ESX-4)) - It is an intracellular bacterium
40
Which agar can be used to distinguish between smooth and rough variants of M. abscessus ?
7H10 agar
41
What are teh selective agars can be used to isolate M abscessus ?
- Wylie-Stanley Agar (WSA) - NTM Elite Agar - 7H10 agar -
42
M abscessus is often multi-drug resistant , list 5 reasons?
- Low cell wall permeability - Absence of drug-activating systems - Efflux pumps - Drug-modifying enzymes - Inducible macrolide R (erm 41 gene) - Acquired resistance : point mutations in: 1) rrl for macrolides 2) rrs for amikacin
43
Which subspecies of M abscesus can have inducible macrolide resistence ?
Due to presence of gene (erm 41) in : - Subspecies abscessus - Subspecies bolletii ------------------------@ Subspecies massiliense lack this resistance
44
Acid-fast organisms other than Mycopacterium spp are?
- Nocardia species - Rhodococcus equi - Cryptosporidium parvum - Isospora belli - Cyclospora cayetanensis - Microsporidia
45
Virulamnce factors for MTB ?
- Cell wall - resist degradation - Survive within macrophages. - Biofilms - Enzymatic neutralization of reactive oxygen species
46
What component of LJ Media that can help M bovis to grow?
Pyruvate
47
Which Mycobacterium that does not grow well in the presence of pyruvate in LJ Media?
- M. xenopi - BCG need to add glycerole
48
Which Mycobacterium culture media to use in CNS TB?
- Kirchner’s liquid media OR: - Middlebrook 7H9
49
List teh 3 recommended testing methods of LTBI?
- Tuberculin skin test (TST) - QuantiFERON-TB Gold In Tube - T-Spot.TB® (Oxford Immunotec)
50
What is the definition of XDR TB ?
R to isoniazid and rifampin, plus any fluoroquinolone and at least one of three injectable second-line drugs (i.e., amikacin, kanamycin, or capreomycin).
51
Mecahnism of IGRA test ?
Detecting a cellular immune response to Mycobacterium tuberculosis
52
what is the Quantiferon IGRA (QuantiFERON-TB Gold In Tube)?
- It is a quantitative measurement of T-lymphocyte secreted interferon-gamma through ELISA - It measures IFN-gamma concentration
53
What is the T-Spot.TB® (Oxford Immunotec)?
- Immunospot assay which provides a direct count of mycobacterial-sensitised T-effector cells. - It measures the number of IFN-gamma-producing cells (spots)
54
Advantage od IGRA test ?
- Requires a single patient visit - No false positive with Prior BCG
55
Disadvantages of IGRA test?
- Cannot distinguish latent TB from active TB - No prognostic value - Limited Value for: (Children <5 / recent exposure<8w / Immunocompromised ) - Expensive - Requires proper sample handling (process sampel within 8-30 h)
56
What are the possible causes of Indeterminate IGRA result?
indicates a test failure due to: - Insufficient IFN-γ response (T-cell dysfunction) - Possible technical issues
57
What is the smooth to rough morhology transition of M abscessus ?
- Result from decrease of surface glycopeptidolipids (GPLs) due to mutations in genes like msp1 - The S variant is considered the colonising form - R variant is associated with increased virulence & can develops cords, which helps prevent phagocytosis.
58
Virulance factors of Mycobacterium abscessus ?
- Ability to form biofilms - Smooth->Rough morphotypes - Enzymes like esterases & proteases - Type VII secretion system - Intracellular bacterium
59
What best agar that can diffrentiate Smooth and rough M abscessus variants ?
Middlebrook 7H10 or horse blood agar
60
Selective culture media for M abscessus growth ?
- Wylie-Stanley Agar (WSA) - NTM Elite Agar - Midlebrook 7H10 agar
61
Antibiotics in WSA media ?
- chloramphenico - ceftazidime - colistin - trimethoprim, sulfamethoxazole, - novobiocin
62
Resistence mechanisms in M abscessus ?
- Low cell wall permeability - Efflux pumps - Drug-modifying enzymes - Inducible macrolide resistance gene (erm 41) - Aquired mutations in rrl for macrolides and rrs for amikacin
63
Standard Tx of Clari sensitive M abscessus ( or with inducible Macrolide R ) ?
- Induction (4 weeks) : IV amikacin + IV tigecycline + IV imipenem + po clarithromycin - Continuations: Neb amikacin + po clarithromycin+ 1- 3 out of the following po : ( clofazimine, linezolid, minocycline or doxycycline, moxifloxacin or ciprofloxacin, and co-trimoxazole)
64
Commonest NTM in pt with pneumoconioses like silicosis ?
M kansasii
65
what are the TB antigens that involved in IGRA testing?
CFP-10 ESAT-6
66
What are the NTM Runyon group 1 ?
- Slow Growers - Photochromogenic - M. kansasii, M. marinum, M simiae
67
What is teh Runyoun group II?
- Slow growers - Scotochromogenic - M. scrofulaceum, M. gordonae, M xenopi
68
Which NTM are rapid growers ?
- M. fortuitum - M. abscessus complex - M chelonae - M smegmatis
69
Which NTM commonly ass with line infection?
M mucogenicum
70
Which NTM commonly ass with corneal infections?
M chelonae
71
Why Qfit plus is more sensitive and specific than Qfit gold in tube ?
- QFTPlus, has an additional TB antigen 2 (TB2) tube to induce cell-mediated (CD8+ T cell) immune responses
72
QuantiFERON-TB Gold Plus (QFT-Plus)
- This ELISA-based assay - Measures the overall concentration of IFNgamma released stimulation with TB antigen -
73
Principle of QuantiFERON-TB Gold Plus (QFT-Plus)?
Uses two separate antigen tubes: - (TB1) primarily stimulates CD4+ T-cell responses - (TB2) is optimized to stimulate both CD4+ and CD8+ T-cell responses.
74
Principles of Tspot test ?
- ELISpot assay - Count the individual T cells that produce interferon-gamma after being stimulated by TB-specific antigens - Uses a mixture of ESAT-6 and CFP-10 peptides to activate T cells.
75
False negative IGRA tests?
TB infection occurred within 8 weeks of testing Advanced HIV infection Advanced immunosuppression, Incorrect sample collection Incorrect handling of tubes Incorrect performance of the assay
76
Extensively drug-resistant tuberculosis (XDR-TB)?
is a form of TB that is resistant to at least four of the main anti-TB drugs (rifampicin, isoniazid, at least one fluoroquinolone and at least one other ‘Group A’ drug)
77
Group A anti TB drugs ?
- Levofloxacin /moxifloxacin - Bedaquiline - Linezolid
78
Group B anti TB ?
- Clofazimine - Cycloserine - Terizidone
79
Group C anti TB drugs include?
- Ethambutol - Pyrazinamide - Delamanid - Imipenem-cilastatin or meropenem, - Amikacin or streptomycin - Ethionamide or protionamide - P-aminosalicylic acid (PAS).
80
Definition of MDR-TB?
R to rifampicin and isoniazid.
81
Definition of pre-XDR?
R to rifampicin isoniazid, and R to at least one fluoroquinolone (either levofloxacin or moxifloxacin).
82
First line TX for MDR or Pre-XDR?
6-month BPaLM regimen Bedaquiline, Pretomanid, Linezolid, and Moxifloxacin.
83
T/F: Note: Moxifloxacin can be omitted (BPaL) for patients with confirmed fluoroquinolone resistance.
T
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