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Collège royal micro 2024 > Mycobactériologie > Flashcards

Mycobactériologie Flashcards

1
Q

Nommer les 5 indicateurs qualité au laboratoire de mycobactériologies (catégories d’indicateurs qualités mentionnés dans le M48)

A
  • Positivité, sensibilité et spécificité des frottis
  • Positivité et taux d’identification (isolation) de MTB et de NTM
  • Turnaround times
  • Taux de contamination
  • Température des incubateurs et des réactifs
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2
Q

What are the 2 different fluorochrome stains that can be used for patient specimens?

A
  • Auramine-rhodamine
  • Auramine-O
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3
Q

What species from the MTB complex is intrinsically resistant to PZA?

A
  • M.bovis
  • M.canettii
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4
Q

2 mycobacteria often associated with tap water contamination.

A

M.mucogenicum
M.chimaera
M.gordonae

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5
Q

Should you grind or minced tissues for mycobacteria culture?

A

Grind

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6
Q

What should be your contamination rate for solid and liquid media? What is the rational behind being in such range of contamination?

A

Under normal circumstances, 2% to 5% of specimens will be overgrown by normal flora for solid media and 7% to 8% for liquid media containing antimicrobial agents.

If over time, contamination rates are more than 5% for solid media, the decontamination technique used is likely inadequate. If the rate is less than 2%, it is too harsh.

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7
Q

Apart from under-decontamination, what other factors should you explore that can lead to high contamination rates?

A
  • Lack of appropriate collection instructions for patients, including when and how to collect the specimen
  • Failure to ensure that specimens obtained at different times are not combined
  • Failure to refrigerate specimens in a timely manner or lack of refrigeration during hold times and
    transport
  • Similar preexamination processing errors that are major causes of contamination during specimen processing
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8
Q

What is the recommended surface area of an AFB smear from a patient specimen?

A

2cm carrés

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9
Q

What are the benefits of using liquid media over solid media?

A
  • Decrease detection time
  • Increase mycobacteria recovery (15-30% more sensitive than solide culture)

Aussi, certaines espèces ne poussent que sur milieu liquide comme M. genavense

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10
Q

Plain LJ is a selective medium, because it contains ______________ _________, which inhibits contaminating bacterial and fungal growth

A

Malachite green

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11
Q

Name 2 types of solid media to recover mycobacteria and 1 example for each.

A
  • Egg based media : Löwenstein-Jensen
  • Agar based media : Middlebrook agars
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12
Q

The optimal temperature for MTBC incubation is :

A

35-37 degrees

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13
Q

Skin, bone and joint biopsy specimens should be incubated at both 37 and at lower temperatures (25-33) for recovery of these 4 pathogens.

A

CHUM :
- M. chelonae
- M. haemophilum
- M.ulcerans
- M.marinum

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14
Q

This mycobacteria needs 40-42 degrees for optimal growth.

A

M.xenopi

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15
Q

Give 3 scenarios where cultures could be held for more than the standard 6-8 weeks (extend to 12 weeks).

A
  • Suspicion of M.ulcerans or M.genavese
  • AFB smear positive but culture negative at 6-8 weeks
  • NAAT was positive but culture is negative at 6-8 weeks
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16
Q

The performance of Middlebrook agar, is optimized in an atmosphere containing ___________ during incubation

A

5-10% CO2

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17
Q

Name 4 agents that can be used for decontamination of specimens.

A
  • NaOH
  • NALC
  • BCP and CPC (only good for LJ media, not compatible with Middlebrook)
  • Oxalic acid (good if a lot of Pseudomonas, eg cystic fibrosis patient)
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18
Q

What is the stain and counter stain of a ZN stain?

A
  • Fuchsin+ phenol, heated
  • Methylene blue
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19
Q

What is the stain and counter stain of a Kinyoun stain?

A
  • Fuchsin+ phenol
  • Methylene blue
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20
Q

Explain how a quantiferon test is conducted and interpreted in the laboratory.

A
  • Multiple commercial tests are available, but the goal of the test is to quantifies release of interferon-γ from lymphocytes in whole blood incubated overnight with three M. tuberculosis antigens with an ELISA.
  • Blood of the patient is mixed in 3 or 4 different tubes.
  • 1 or 2 tubes contain TB antigens (early secretory antigen target-6 (ESAT-6), culture filtrate protein-10 (CFP10), and TB7.7).
  • 1 tube contains nothing but heparin
  • 1 tube contains mitogens
  • After incubation, if either antigen tube produces more interferon-γ than the nil (no antigen) tube, the result is positive. If the mitogen tube does not produce more interferon-γ than the nil tube, the result is indeterminate.
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21
Q

4 Mycobacteria that can cause a false positive quantiferon.

A

Can have false positive with exposures to M.kansasii, M.szulgai, M.marinum, M.flavescens

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22
Q

In Canada, at what age can we start using the IGRA?

A

2 years old

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23
Q

The Canadian TB standards mentions 1 situation where a TST is preferred over the IGRA.

A

The tuberculin skin test is the preferred test when serial testing is planned to assess risk of new infection (ie, conversions). This includes repeat testing in a contact investigation, or serial testing of health
care workers or other populations (eg, corrections
staff or prison inmates) with potential for ongoing
exposure. In these situations, interferon-gamma
release assays are not acceptable.

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24
Q

All available experimental and epidemiologic evidence consistently shows that TST conversion occurs within __________ of exposure.

A

3-8 weeks

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25
Q

What 4 groups of people with a positive TST are considered VERY high risk of developing active TB?

A
  • HIV patients
  • Child or adolescent with TB contact
  • Adult with TB contact
  • Silicosis
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26
Q

Definition of MDR-TB

A

resistant to isoniazid and rifampin with or without resistance to other first line anti-TB drugs

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27
Q

Definition of pre-XDR and XDR-TB

A

Pre-XDR-TB, which is now defined as MDR-TB (resistant to isoniazid and rifampin with or without resistance to other first line anti-TB drugs) with additional resistance to any fluoroquinolone; and XDR-TB, which is defined as pre-XDR-TB with additional resistance to bedaquiline or linezolid.

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28
Q

TB standards : We conditionally recommend, for the treatment of MDR-TB, the following five drugs as the initial regimen in the absence of drug susceptibility testing-proven resistance or contraindications:

A
  • Bedaquiline
  • Pretomanide
  • Levoflox or moxiflox
  • Cycloserine
  • Clofazimine
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29
Q

What is the recommended duration of treatment for MDR and XDR TB?

A

18-20 months according to Canadian TB standards, but the WHO standards say you can do 6 months with BPLM regimen.

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30
Q

Quel peut être un marqueur indirect de TB sur CSF ou liquide péritonéal/pleural?

A

Adénosine déaminase - attention non recommandé au Canada car haut taux de faux positif secondaire à empyème/cancer.

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31
Q

Décrire le traitement MAC non-cavitaire non-sévère VS MAC sévère cavitaire, et la durée minimale du traitement.

A
  • Azithro (>clarithro) + RIF + EMB
  • Azithro (>clarithro) + RIF + EMB + amikacine
  • 12 mois minimal APRÈS négativation des cultures
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32
Q

Décrire le traitement de M.kansasii, et la durée minimale du traitement.

A
  • RIF + EMB + (INH or AZITHRO)
  • 12 mois minimal APRÈS négativation des cultures
33
Q

Décrire le traitement M.xenopi non-cavitaire non-sévère VS M.xenopi sévère cavitaire, et la durée minimale du traitement.

A
  • RIF + EMB + (macrolide or moxifloxacine)
  • Sévère : ajouter amikacine
  • 12 mois minimal APRÈS négativation des cultures
34
Q

What are the 3 species in the M.abscessus complex?

A

M.abscessus subs abscessus
M.abscessus subs boleti
M.abscessus subs massiliense

35
Q

What are some parenteral and oral agents active against M.abscessus?

A

Parenteral :
- Imipenem
- TMP-SMX
- Amikacin
- Tigecyeline

Oral :
- Azithromycin
- Clofazimine
- Linezolid

36
Q

2 agents causant la lèpre.

A

Mycobacterium leprae > > M. lepromatosis

37
Q

5 formes de lèpre.

A

tuberculoide (TT)
borderline tuberculoide (BT)
mid-borderline (BB)
borderline lepromateuse (BL)
lepromateuse (LL)

38
Q

What is the best stain on full thickness skin biopsy to diagnose leprosy?

A

Fite stain

39
Q

3 antimicrobials active against leprosy.

A
  • Dapsone
  • Clofazimine
  • Rifampicin
40
Q

Décrire schéma de traitement de l’actinomycose.

A
  • 1er choix : Penicilline G ou amoxil
  • 2-6 semaines IV puis 6-12 mois PO total
  • Étendre 12 à 18 mois total si :
    1) Immunosupprimé
    2) VIH
    3) Infection invasive
41
Q

A nitrate reduction test is valuable for identifying : (4)

A

M. tuberculosis, M. kansasii, M. szulgai, and M. fortuitum.

42
Q

Name 4 photochromogens

A

-M simiae
-M marinum
-M kansasii
-M asiaticum

43
Q

Name 4 scotochromogens

A

-M xenopi
-M szulgai
-M gordonae
-M flavescens

44
Q

Résistance MTB à l’INH: Quel gène confère une résistance de bas niveau et quel gène confère une résistance de haut niveau?

A

Bas niveau: inhA
Haut niveau: katG

45
Q

Selon les Canadian TB Standards, 8e edition, quels sont les 2 options de première ligne pour le tx de la TB latente

A

Rifampin DIE x 4 mois
Rifapentine + INH 1x par semaine pour 3 mois

46
Q

Groupes pour lesquels un PPD de =>5mm est considéré comme positif.

A
  • People living with HIV
  • Known recent (<2 years) contact with a patient with infectious TB disease
  • Fibronodular disease on chest x-ray (evidence of healed, untreated TB)
  • Prior to organ transplantation and receipt of immunosuppressive therapy
  • Prior to receipt of biologic drugs, such as tumor necrosis factor alpha inhibitors, or disease-modifying antirheumatic drugs
  • Prior to receipt of other immunosuppressive drugs, such as corticosteroids (equivalent of ≥15mg per day of prednisone for
    at least one month)
  • Stage 4 or 5 chronic kidney disease (with or without dialysis)
47
Q

On peut considéré un PPD positif comme un vrai positif si un patient a reçu un BCG chez ces groupes :

A
  • BCG administrer dans la première année de vie et TCT fait après l’âge de 10 ans.
  • La personne fait partie d’un groupe dans lequel le taux de prévalence de TBL est élevé
  • La personne présente un risque élevé de contracter la maladie si elle est infectée.
48
Q

Selon les Can TB standards 2022, quelles sont les deux indications reconnues de donner des corticostéroïdes en plus d’une thérapie antituberculeuse?

A
  1. Péricardite TB chez non VIH
  2. Méningite tuberculeuse (pas pour le tuberculome isolé)
49
Q

The major advantage of computed tomography CT is
increasing the ____________ of the diagnosis of TB.

A

Specificity

50
Q

Quelle est la température à laquelle conserver les spécimens pour culture de mycobact qui ont un délai de transit >1h? Quels spécimens sont exempt de cette méthode?

A
  • 2-8°C, ne pas congeler
  • Sang et LCR : garder à température pièce
51
Q

What are the 4 key factors affecting sensitivity of AFB smear?

A
  • Quality of specimen (respiratory > > everything else)
  • Stain used
  • Time used to read the smear
  • Experience of the microscopist
52
Q

Pour les spécimens à très faibles volumes (<2mL), est-ce que la culture ou la coloration doit être priorisée?

A

Toujours prioriser la culture (peut détecter 10 micro-organismes / mL vs le NAAT environ 100/mL vs la coloration fluorescente 5 000 - 10 000/mL vs coloration ZN 100 000/mL)

53
Q

What is the sensitivity of NAAT on smear positive/culture positive samples VS smear negative/culture positive samples?

A
  • > 95%
  • 50-70%
54
Q

What kind of molecular assay is the Xpert MTB/RIF©? What is the sensitivity and specificity of that assay?

A
  • cartridge-based, automated, nested, real-time PCR
  • pooled median sensitivity and specificity were 88% (83%, 92%) and 98% (97%, 99%)
55
Q

Apart from Expert MTB/RIR assay, name 4 other molecular tests for TB approved by Health Canada.

A
  • Roche (COBAS® Taqman® MTB; real-time-PCR)
  • Becton Dickson (BD ProbeTec®, strand displacement amplification);
  • Gen-Probe (Amplified Mycobacterium tuberculosis Direct, [AMTD], transcription mediated amplification);
  • Hain Lifescience (GenoType® Mycobacteria Direct, PCR)
56
Q

Name 1 gene that can be sequenced to differentiate species in the MTB complex.

A

gyrB

57
Q

________________ is still considered the gold standard for MTBC
drug susceptibility testing (DST). However, because of the labor-intensive nature and lengthy incubation time for the assay, the more rapid ______________________ are now recommended.

A
  • Agar proportion (Canetti’s proportion method)
  • Liquid media detection methods using continuous monitoring systems
58
Q

Name 3 methods to perform AST for Mycobacteria.

A
  • Mitchison’s “Resistance-Ratio” Method
  • Canetti’s “Proportion Agar” Method
  • MGIT liquid media detection method
59
Q

For Quantiferon TB gold, what are some common factors causing unreliable or indeterminate results?

A
  • technical failure, including improper protocol
  • excessive levels of circulating IFN-γ or the presence of heterophile antibodies
  • greater than 16 hours between time of blood draw and incubation at 37 °C
  • storage of blood outside ambient temperature range (17-25 °C)
  • insufficient mixing of blood collection tubes
  • incomplete washing of the ELISA plate.
60
Q

Quelles procédures doivent être surveillées pour leurs turn around time au labo TB?

A
61
Q

Pour qu’un Quantiferon TB gold soit considéré comme positif, quelle doit être la valeur du TB1 and /or TB2 antigen minus nil (IU/mL)

A

=>0.35 et =>25% de la valeur dans le tube “nil”

62
Q

Quelles sont les températures d’incubation des mycobact et quelles mycobact peut croitre en fonction des différentes températures?

A

35-37: pour la majorité
25-33: M. chelonae, M. haemophilum, M. ulcerans et M. marinum
40-42: M. xenopi

63
Q

Mutations in what genes confers resistance to ethambutol?

A

embB

64
Q

Mutations in what genes confers resistance to pyrazinamide?

A

Mutation in the gene encoding PZase : pncA

65
Q

Name 4 species of the MTB complex.

A

-M tuberculosis
-M africanum
-M bovis (cattle)
-M caprae (cattle)
-M microti (rodents)
-M pinnipedii (seals)
-M orygis (antelope)
-M mungi (mongoose)

66
Q

What is defined as the lowest concentration of an antituberculous agent in vitro that will inhibit the growth of 99% of phenotypically wild-type strains of MTBC?

A

Critical concentration

67
Q

What are the main challenges with molecular MTBC AST?

A
  • Poor reproducibility for RIF : False resistance has been reported for direct probe-based molecular methods when small or marginal amounts of DNA are present, such as in some AFB smear-negative specimens.
  • Detection of silent mutations (Direct probe-based molecular methods can detect nucleotide changes due to lack of hybridization to a probe, but some of these changes do not cause a change in the functional change in the gene product)
  • Detection of disputed mutations (A disputed mutation refers to a mutation that does not confer drug resistance by culture based AST)
  • Heteroresistance : MTBC cultures may contain a mixture of susceptible and resistant bacilli. Failure to detect resistance, due to the presence of small quantities of resistant bacilli along with larger quantities of susceptible bacilli, can lead to development of drug resistance and treatment failure over time.
68
Q

What is the drug that is most problematic in a short incubation broth system?

A

Ethambutol : Short-incubation broth systems may detect less resistance than agar proportion.

69
Q

In general, molecular AST can be categorized into two major types:

A
  • sequencing-based methods
  • probe-based methods.
70
Q

Mutations in what genes confers resistance to FQ?

A

gyra

71
Q

Mutations in what genes confers resistance to bedaquiline?

A

atpE

72
Q

Mechanisms of action of bedaquiline and pretomanid (1st line MDR agents)?

A
  • Bedaquiline : inhibits adenosine triphosphate synthase (an enzyme necessary to maintain energy supply in the cell)
  • Pretomanid : inhibits cell wall biosynthesis via blockage of the oxidation of hydroxymycolate
73
Q

The recommended standard NTM AST procedure is :

A

Broth microdilution

74
Q

__________________ are the only antimicrobial agents for which correlation between MAC in vitro susceptibility tests and clinical response has been demonstrated in controlled clinical trials.

A

Macrolides
Amikacin

Il y a aussi des breakpoints pour Moxi et Line dans le CLSI

75
Q

MAC AST : although these 2 drugs are in the recommended treatment regimen, breakpoints for these agents that separate susceptible from resistant strains cannot be determined, so these drugs should not be reported.

A
  • RIF
  • EMB
76
Q

Traitement infection cutanée à M.marinum.

A
  • Clarithro ou azithro + EMB ad 1-2 mois de résolution complète des lésions
77
Q

MAC : mutations in what gene can cause macrolide resistance?

A

23S rRNA gene mutation

78
Q

Pour quels agents anti microbiens existe-t-il des MIC (et non des critical breakpoints) pour MTBC?

A
  • RIF
  • EMB
  • INH
79
Q

Quelles sont les activités autorisées en NC2+ avec des cultures de MTB?

A
  • incubating and reading initial diagnostic cultures (i.e., excluding subcultures) in tightly capped/sealed tubes, such as MGIT™, Bactec™, and Lowenstein-Jensen
  • non-propagative assays on initial diagnostic cultures needed to confirm AFB or TB (e.g., preparation and reading of smears) can be performed at CL2
  • aliquoting diagnostic cultures for inactivation (e.g., for DNA Probe), for packaging, and for shipping can be performed at CL2

Collège royal micro 2024 (18 decks)

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