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Cardio > Microbiology TB > Flashcards

Microbiology TB Flashcards

1
Q

Classification

A
  • M. tuberculosis (MTB) complex (Typical)

* MOTT (mycobacteria other than TB) (Atypical or Non-tuberculous mycobacterium (NTM)) – more difficult to manage.

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2
Q

MTB Complex

A
  • M. tuberculosis
  • M. bovis (inc. BCG)
  • M. africanum
  • M. microti
  • M. canetti
  • M. caprae
  • M. pimmipedii
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3
Q

Non-cultivatable mycobacterium

A

• M leprae

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4
Q

Runyon Classification (1959) MOTT

A

Atypical mycobacterium
• I Photochromogens → Yellow pigment formed after exposure to light when colonies grown in the dark and take more than 7 days
• II scotochromogens → Yellow or orange pigment formed when colonies grown in the dark and take more than 7 days
• III Nonphotochromogens → Colonies are non-pigmented regardless of whether grown in the dark or light and take more than 7 days
• IV Rapid growers → colonis (pigmented or non- pigmented) that take less than 7 days

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5
Q

Rapid growers

A

Non Chromogens →
Chromogens
See page 110

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6
Q

1

A

Number of tubercle bacilli required to establish infection

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7
Q

10

A

Average number of people that get infected by a single case of pulmonary TB

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8
Q

15

A

Number of years for which the incidence of TB has been progressively increasing in the UK

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9
Q

20

A

Time in hours for M. tuberculosis, a slow growing mycobacterium, to replicate

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10
Q

130

A

Hours of exposure to a case of infections pulmonary TB needed to be sure of contracting TB infection

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11
Q

6,669

A

Number of cases of TB in the UK in 2001

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12
Q

2,500,000

A

Annual number of deaths due to TB globally

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13
Q

Mycobacterium Tuberculosis → Description

A

Human pathogen

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14
Q

Mycobacterium Tuberculosis →Transmitted by

A

Respiratory droplet (infectious dose: 1-10 bacilli)

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15
Q

Mycobacterium Tuberculosis →Adapted to

A

Intracellular survival within the human macrophage
• Latency/dormant/non-replicating persistence
• Allows lifelong infection

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16
Q

Mycobacterium Tuberculosis →Factors that promote progression to active disease

A 
HIV
•	At all CD4 counts
•	More extrapulmonary disease
Immunosuppressive drugs (iatrogenic)
•	High dose steroids
•	Infliximab (anti-TNF w/ latent TB due to T-cells)
Age: very young; very old
Poor nutrition
Homelessness/alcohol/ IVDA/ poverty
17
Q

Patients with active disease

A

Treat especially with infectious pulmonary tuberculosis

18
Q

Vaccination

A

Limited and variable efficacy (UK vs India; prevents dissemination)
Age 12-14, or at birth if parents are from high-risk groups.

19
Q

Diagnose people with latent tuberculosis infection and give preventative therapy

A

1 infections case infects 10 other people, of whom 1 will develop TB
Tuberculin skin test (Heaf): cross-reactivity of PPD with BCG
Contact tracing
New arrivals from high prevalence areas
Child contacts

20
Q

Diagnosis →

A

Specimens
Procedures
Culture
Histology

21
Q

Specimens

A

Sputum, gastric washings, bronchoalveolar lavage
Early morning urines
Biopsies

22
Q

Procedures

A

Microscopy (result within 24 h; not all AFBs are TB)
• Ziehl-Neelson
• Auramine

23
Q

Culture

A

Crucially important, but often negative)
Solid phase: Lowenstein-Jensen medium
Liquid phase: uptake and release of radiolabelled carbon
Drug sensitivities

24
Q

Histology

A

Granulomata with central caseous necrosis

25
Q

Drawbacks of Tuberculin Skin Test →

A

Poor specificity
Poor sensitivity
Operational drawbacks

26
Q

Tuberculin Skin Test Poor specificity

A

Antigenic cross-reactivity of PPD with BCG and environmental mycobacteria

27
Q

Tuberculin Skin Test Poor sensitivity

A

75-90% in active disease (lower in disseminated TB and HIV infection, unknown for latent infection.

28
Q

Tuberculin Skin Test Operational drawbacks

A

Need for return visit
Operator variability (inoculation and reading)
Standardisation of reagent
Painful inflammation and scarring

29
Q

In-vitro and in-vivo diagnostic tests

A

APC presenting mycobacterial antigens to memory T-cells

See diagram page 112

30
Q

ELISPOT principle of test

A

RD1 contains the genes for ESAT6 (early secretory antigen target 6) and CFP10 (culture filtrate protein 16)
→ doesn’t give a false +ve w/ BCG as the genes aren’t in BCG bt +ve result = low risk popn
→ Can’t be –ve in patients w/ active disease

31
Q

Definition resistant TB

A

MDR-TB (Multidrug Resistant TB) describes strains of tuberculosis that are resistant to at least the two main first-like TB drugs – isoniazid and rifampicin.

32
Q

XDR-TB or Extensive Drug resistant TB (also referred to as Extreme Drug resistance)

A

Is MDR – TB that is also resistant to three or more of the six classes of second-line drugs.

33
Q

MDR-TB

A

Resistance to anti-TB drugs in populations is a phenomenon that occurs primarily due to poorly managed TB care. Problems include incorrect drug prescribing practices by providers, poor quality drugs or erratic supply of drugs, and also patient non-adherence.

34
Q

Risk assessment for MDR-TB

A
  1. History of prior TB drug treatment, prior TB treatment failure
  2. Contact with a known case of durg-resistant TB
  3. Birth in a foreign country, particularly high-nicidence countries
  4. HIV infection
  5. Residence in London
  6. Age profile, with highest rates between ages 25 and 44
  7. Male gender
35
Q

XDR-TB

A
  1. First described in 2006
  2. During 2000-20004, of 17, 690 TB isolates referred to international network of TB laboratories, 20% were MDR nd 2% were XDR
  3. In addition, population-based data on drug susceptibility of TB isolates were obtained from the United States (for 1993-2004), Latvia (for 2000-2002), and South Korea (for 2004), where 4%, 19% and 15% of MDR TB cases, respectively, were VDR
36
Q

Resistant TB →

A

A tuberculous cavity contains 107 to 109 bacilli. If mutations causing resistance to INH occurs in 1 in 106, and mutations causing RIF resistance occur in about 1 in 108, the probability of spontaneous MDR is 1 in 1014.

37
Q

Treatment of resistant TB (non-MDR)→

A

)→ resistant to 1 or 2 → streptomycin.
Depends on site = initiation phase (4 drugs for 2 months), (2 drugs for 4 months).

4 drugs used:

  1. Rifamapicin
  2. Ioniaziad
  3. Perizonamide
  4. Ethanbutol

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