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Microbiology Virology > Μ. Tuberculosis > Flashcards

Μ. Tuberculosis Flashcards

1
Q

Mycobacteria genus: classification
staining?/ what’s in cell wall?/ what’s in DNA

A

-Acid-fast staining (Ziehl- Neelsen)
_ mycolic acids in cell wall
- high G+C content in DNA

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2
Q

What else stains acid fast?

A

Nocardia spp

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3
Q

Mycobacteria: culture?

A

Weeks are required for culture

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4
Q

M. Tuberculosis another name?

A

Koch’s bacillus

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5
Q

• M. tuberculosis treatment making it curable.

A

Curable: Rifampin

Mostly curable : streptomycin + isoniazid

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6
Q

Rates of TB increase when…

A

HIV infxn increases

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7
Q

URGENT worldwide threat , how?
(For TB)

A

Spread multi- resistant TBC(MDR) + extensively resistant TBC (XDR)

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8
Q

M. Tuberculosis cause most of what

A

M. tuberculosis causes the vast majority of human tuberculosis
HUMANS ARE ONLY RESERVOIR

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9
Q

M. tuberculosis:

M. bovis?

A

M. bovis (cattle TBC, spreads to humans by consumption of unpasteurized milk),

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10
Q

M. tuberculosis
Characteristics

A

‘Aerobic, non-spore forming, acid-fast ROD,(visible growth takes 3-8wks on solid media-culture)?

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11
Q

DIAGNOSING- M. Tuberculosis
Acid fast stain

A

Ziehl-Neelsen (Kinyoun stain): any fluid can be examined.

Sputum: around 10,000 bacilli/ml of sputum smear POSITIVITY

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12
Q

M. Tuberculosis Diagnosis

A
  1. Acid-fast stain (Ziehl- Neelsen)
  2. Culture
  3. NAATs (Nucleic acid amplification tests)
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13
Q

M. TB diagnosis
Culture

A

Any fluid/tissue can be cultured
Solid media (3-8wks) liquid media 1-3wks

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14
Q

M. tuberculosis- diagnosis
Nucleic acid amplification tests (NAATs)

A

PCR, highest sensitivity for sputum samples, able to detect resistance genes

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15
Q

‘M. tuberculosis - immunology
To control…
Relies on … + cytokines …

A

-To control, requires cellular immunity.
- relies on CD4 t-cells + cytokines IFN-γ & TNF (tissue damage by cellular immunity facilitates cavitation of lung + transmission of M. Tb by cough)
So we need them

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16
Q

M. tuberculosis - pathogenesis
/ mode of transmission

A
  1. ! Airborne secretions containing tubercle bacilli reach terminal air spaces
    …
17
Q

What population is susceptible to M. TB

A

Patients with HIV infection (low CD4 T-cell counts) & patients under antiTNF therapy are extremely susceptible to disease progression or reactivation

18
Q

M. tuberculosis primary infxn
(Ghon+ ranke)

A

Ghon focus/ lesions- initial lung focus can be necrotic and calcify
Ranke complex= extends to regional nodes (calcified nodes) , (parenchymal +mediastinal node calcification )

19
Q

Miliary TB

A

If caseous (cheese-like) necrotic material reaches lymph or blood (dissemination)

20
Q

Pulmonary TB
Epidemiology

A

Children <5y/o = prone to lymphatic dissemination (+ military TB)

21
Q

ALWAYS THINK TBC
…

A

PNEUMONIA (esp. in apices) PLUS HILAR ADENOPATHY

22
Q

Cavity favours a lot……….

A

Cavity favours multiplication of bacilli
extremely infectious secretions

23
Q

Symptoms & signs of Pulmonary tb

A

Symptoms & signs: persistent fever, weight loss, anorexia, cachexia, haemoptysis (coughing blood) , persistent cough

24
Q

Pulmonary tuberculosis diagnosis

A

’ 3 morning sputum specimens: Ziehl-Neelsen stain, PCR & culture – both in liquid & solid media

Ask 2 questions 1. Are there Mycobacteria inside sputum? (meaning is Ziehl-Neelsen staining or culture positive?)
2. Are these M. tuberculosis? (PCR)

25
Q

Tuberculosis transmission

A

Inhalation of droplet nuclei (<5μm) – infectious particles from patient with pulmonary disease, remain in air for long

Large drops of respiratory secretions- not transmitted.

Transmission does not generally occur outdoors – bacteria killed by UV light
Rare- ingested milk with M.bovis

26
Q

.. Airborne precautions

A

CONFIRMED OR SUSPECTED pulmonary, laryngeal or pleural TBC must be ISOLATED in
negative pressure rooms. • Extrapulmonary TBC IS NOT transmittable, isolation NOT required!

27
Q

-Airborne precautions
Tb

A

Patients placed in isolation rooms with NEGATIVE pressure – Door ALWAYS CLOSED.
Everyone entering room of pts. With suspected/ confirmed TB must wear N95 mask [respirator that filters 1-μM particles with efficiency of at least 95%]
Mask should fit tightly

28
Q

1.Time until you become non infextious…
2. Patients with smear positive sputum
3.Patients with smear negative sputum, but positive sputum culture
4. Patients with smear negative sputum & negative sputum culture

A
  1. 2 wks after tx started for sensitive TBC
  2. Patients with smear(stain) positive sputum = HIGHLY CONTAGIOUS
  3. Patients with smear negative sputum, but positive sputum culture = LESS CONTAGIOUS
  4. Patients with smear negative sputum & negative sputum culture = NON-CONTAGIOUS
29
Q

Extrapulmonary tuberculosis – REMEMBER every organ can be affected
Miliary TB

A

Haematogenous spread, soon after primary infection in children or as terminal event in untreated TBC, usually immunosuppressed

All organs affected – diagnosis usually made with tissue biopsy (usually transbronchial biopsy)

30
Q

Extrapulmonary tuberculosis

CNS tuberculosis – tuberculous meningitis
+ diagnosis

A

¾ have evidence of extra-CNS TBC, miliary shadowing is most suggestive - fever, extreme headache
with confusion, meningismus, cranial palsies
• CSF pleocytosis (with lymphocyte predominance), very low glucose, very high protein levels
• HIGH MORTALITY – CSF: Ziehl-Neelsen stain, culture, PCR

31
Q

Extrapulmonary tuberculosis

Skeletal TBC – Pott’s disease

A

Lower thoracic spine more frequently, followed by lumbar: evidence of other foci often ABSENT
• Paraspinal cold abscesses present in 50% - ½ have weakness or paralysis of lower extremities
• Surgical drainage immediately if symptoms of weakness or paralysis

32
Q

Extrapulmonary tuberculosis
Genitourinary Tb

A

STERILE PYURIA the most prominent finding - culture of 3 morning urine specimens or urine PCR

*pyuria= pus / WBC in urine

33
Q

Latent tuberculosis
(Important to know if they’ve had it before as it’s dormant)
TST (tuberculin kin test) or Mantoux
+ technique

A

Injection of Purified Protein Derivative (PPD) of M. tuberculosis intradermally Technique • A dose of 5-TU (tuberculin units) is injected intradermally on volar aspect of forearm
• Correct injection produces a raised, blanched, 6- to 10- mm wheal (red, swollen mark)
• Skin reaction is based on presence of type IV hypersensitivity reaction from cellular immunity
• Reaction read in 48-72hrs – measure induration NOT ERYTHEMA
• Use point ballpoint pen to draw a line starting 1 to 2 cm away from skin reaction & move toward its
center. Pen lifted when resistance felt. Procedure repeated from opposite direction. The distance between opposing line ends measured

34
Q

Tuberculin Skin Test – TST or Mantoux
Who to test
Only for latent

A

• Persons at high risk for developing TBC or those for whom latent TBC must be excluded
• Recent immigrants, health-care workers, TBC contacts, conditions that increase risk for TBC (HIV+, transplants etc.), ! patients ready to start antiTNF therapy !
If positive, active TBC must be excluded (x-ray + physical examination), and if active TBC is
excluded, Tx for latent TBC must be administered

35
Q

Tuberculin Skin Test – TST or Mantoux
False positive results

False negatives

A

Prior BCG vaccination (if they’re previously vaccinated) or infections from non-tuberculous mycobacteria

False negatives:
• May occur in up to 20% of those with active TBC
• Malnutrition, HIV with CD4<200, sarcoidosis, corticosteroid Tx, vaccination with live viral vaccines

36
Q

IGRA – Interferon γ-release assays
(To rest if they’ve been vaccinated or latent)
More expensive

A

•Same purpose as TST – ADVANTAGE: not influenced by prior BCG vaccination or infections by non-TB mycobacteria
• blood test- lymphocytes from tester pt incubated overnight in presence of M. TB antigens- IFN-γ release measured
• • If lymphocytes were previously exposed to M. tuberculosis, IFN-γ is released

37
Q

Vaccine - BCG

A

Attenuated, live - Bacillus of Calmette & Guerin (BCG) strain of M. Bovis
In countries with a lot of TB protects mostly from TB meningitis + Miliary TB in children- LIMITED PROTECTION AGAINST PULM. Disease
BCG interferes with TST positivity n is also see for non invasive bladder cancer

Microbiology Virology (7 decks)

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