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Microbiology > M24 - TB > Flashcards

M24 - TB Flashcards

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Biology 101 flashcards
1
Q

what is the obligate pathogen of tuberculosis?

A

Mycobacterium tuberculosis

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2
Q

what percentage of infected develop tuberculosis?

A

5-10%

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3
Q

How long does primary TB take to develop?

A

1-2 years

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4
Q

who is tuberculosis associated with?

A

disseminated disease associated with children

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5
Q

when and why does post-primary TB occur?

A

later in life and involve re- activation of organism

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6
Q

what is TB linked to?

A

immune status (e.g HIV)

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7
Q

what is the resistance rate of TB?

A

1.5-6% - stable

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8
Q

How many bacteria need to be inhaled to cause disease?

A

3

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9
Q

Describe the steps of pathogenesis of TB.

A
  • Inhalation (3 bacteria)
  • Penetrate deep into lung alveoli
  • Initial lesion formed after entry into pulmonary epithelium & macrophages
  • Phagocytosis, phagolysosome acidification arrested (LAM)
  • Persist & replicate
  • Induce localised immune response & recruit macrophages
  • Destroy cells & infect new cells especially macrophages
  • Granulomatous lesion forms
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10
Q

Describe the steps of the persistent infection of TB.

A
  • Myco tb & cell wall fragments taken to lymph nodes
  • Prime T cells & in turn stimulate more macrophages
  • Immune response localises but leads to more macrophages becoming infected.
  • Infected macrophages continue to escape & disseminate organism to lymph nodes, spleen, kidneys etc.
  • Innate & adaptive immune response normally controls infection (2-6 weeks)
  • Leaves behind infected macrophages & in some individuals tubercle
  • Bacteria either lay dormant or lyse cells, escape and infect more macrophages.
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11
Q

Name the 5 stages of how TB has its effect.

A
  1. Bacilli inhaled into the alveoli and ingested by macrophages
  2. Bacilli multiply in macrophages
    & cause more macrophage to migrate to the site of infection
  3. After several weeks, many of the macrophages
    die releasing Mycobacteria and forming caseous centre surrounded by mass of macrophages & lymphocytes Disease dormant
  4. Mature Tubercle formed
    Outer firm layer of fibroblasts
    Caseous centre enlarges by liquefaction Forming cavity in which bacilli multiply
  5. Tubercle ruptures Bacilli spill into bronchiole & are disseminated throughout the body.
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12
Q

When is it likely for the reactivation of tuberculosis?

A

If primary lesions fail to heal by becoming fibrous & calcified can lead to Tubercle that is prone to reactivate

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13
Q

Describe the reactivation of tuberculosis.

A

• Dormant bacteria survive Tubercle & escape in relatively high numbers
• Organisms shed in sputum & individual is highly infective
• Also spreads in the body and causes new sites of infection
• Reactivation can be linked to immune system
– e.g. Age, stress, malnutrition, alcoholism, immunosuppressive
drugs or diseases.
• Damage to lung & other tissue leads to debilitating cycle of disease that ultimately can lead to death

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14
Q

What are the likely hood of symptoms developing?

A

• Infection limited to lung
(majority)
• Cellular immunity halts replication within 2 to 6 weeks. Most hosts unaware of infection.
• 10% progress to disease state, 5% in first 2 years

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15
Q

What are the initial symptoms innocuous?

A
  • Malaise
  • Weight loss (appetite)
  • Cough
  • Night fever/sweats
  • Productive cough (sputum)
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16
Q

What does sputum stained with blood (hemoptysis)?

A

indicates tissue

destruction or cavitary disease

17
Q

Describe the diagnosis of TB.

A
  1. +ve skin test using tuberculin (mixture of TB Ags)
  2. Radiographic evidence of pulmonary disease.
  3. Laboratory diagnosis of Mycobacteria
18
Q

Describe the tuberculin skin test.

A

• Purifiedproteinderivative
– Consists of cultured filtrates of
organism
– Injected intradermally in forearm
– Read 48 to 72 hours later
– Presence and size of swollen hardened area read >10mm
– Detects presence of sensitized T Cells

19
Q

How long after initial contact can tuberculin skin test get a positive reaction?

A

6 weeks

20
Q

Describe the characteristics of mycobacterium.

A
  • Non-motile
  • Non-Sporeforming
  • Aerobic bacilli
  • Complicated cell wall that is rich in lipids and when stained cannot be decolourised with acid solutions
  • High GC content
  • Fastidious
  • Slow Growing (12-24h)
21
Q

Describe mycobacterium’s waxy cell wall.

A

• CellWall
– 60% Lipid
– Mycolic Acids
– Complexed with polysaccharides & peptides producing strongly hydrophobic waxy cell wall
– Cord Factor toxic to mammalian cells & inhibits migration of PMN cells
• Lipoarabinomannan

22
Q

Describe the laboratory diagnosis.

A

Sputum specimen taken
– Microscopic analysis
• Smears examined for acid fast bacteria
• Or fluorescent antibody detection 50% accurate
• Culturing
• Solid media Lowenstein-Jensen media (4-8 weeks)

–  Nucleic Acid Amplification
•  Amplification of 16S rRNA 
–  Sensitivity 75-100%
–  Specificity 90-100%
•  PCR of M.tb genes
–  As specific as culturing and results within 8 hours.
23
Q

What is the treatment?

A 
•  Long course of antibiotic treatment (6-9 mths) :
– Isonazid (primary antibiotic)
–  Rifampicin
–  Pyrazinamide (first 2 months)
–  Ethambutol (first 2 months)
24
Q

What is the control?

A

Vaccination:
– Bacille Calmette-Guerin (BCG)
– attenuated M. bovis
• Enhances ability of macrophages to become activated and kill bacteria
• >70% protective against serious forms of the disease
• UK targeted policy (areas > 40 per 100,000)

25
Q

What is the problems with UK drugs against TB?

A

Drug resistance

26
Q

Describe the drug resistance worldwide.

A

• 65% Rise in Drug resistance strains since 2006
• 650,000 case of MDR TB
-Multi Drug resistance (isonazid & rifampicin)
-Only 50% treated cured
• 58,500 cases of XDR TB
- Extensive Drug resistance
- Resistance to 4 or more Drugs

27
Q

Describe oral tuberculosis.

A

• Normally secondary lesions
• OccurrenceofAIDShas
increased prevalence
• Lesions normally found at back of the mouth
• E.g Cervical Lymph nodes
initially swollen by several cms firm but mobile
develop to become fixed with abscess & sinus formation

28
Q

Describe mycoplasma pneumoniae.

A

• Primary atypical Pneumonia
• Transmitted by respiratory
droplets
• Lower respiratory tract infection
• Sporadic occurrence (occasional epidemics)
• Most common in in 6-20 year age group, re-infection common and usually more severe

29
Q

What are the symptoms of mycoplasma pneumoniae.

A 
•  Gradual onset
•  Non-specific symptoms
–  Unrelenting headache
–  Fever, chills, malaise
•  2-4 days dry unproductive cough
•  Diffuse bronchopneumonia involving one or more lobes (detected by X-ray)
•   " Walking pneumonia "
•  Remits after 3 to 10 weeks
•  Immuno-compromised most likely to suffer complications
–  CNS disturbance
–  Rash
–  Mild hemolytic anemia
30
Q

Describe the mycoplasma species.

A

• Smallest free-living organism
– 0.3 ums in diameter
– Vary in shape (coccal & filaments)
– No cell wall
– Difficult to stain
– Fastidious & difficult to culture
• Culture media
– Enriched, yeast extract, serum & sterols
– 37 ̊C CO2, colonies appear after 7 days
– Fried egg appearance

31
Q

Describe the transmission of mycoplasma species.

A

– Respiratory droplets

– Organism shed in saliva prior to disease

32
Q

Describe the pathogenesis of mycoplasma.

A

– Infiltration of lymphocytes & macrophages leads to thickening of cell walls of alveoli & bronchioles

33
Q

Describe the diagnosis of mycoplasma.

A

– Sputum analysed by nucleic acid hybridisation
• 16S ribosomal RNA
– Serological tests
• 4xs rise in complement fixing antibody
• Detection of IgM antibody to P1 produced by 60% of patients. Can be detected by ability to reverse the agglutination of red blood cells between 0 ̊C & 4 ̊C

34
Q

Describe the treatment of mycoplasma.

A

– Erythromycin or Tetracycline

35
Q

What is the problem with the treatment of mycoplasma?

A

Slow growing - slow to respond to treatment & may persist in upper respiratory tract

36
Q

Give a summary slide.

A

•GDPs exposed to Respiratory tract pathogens – Diagnosis, complications, treatment,
•Include H.influenza , C. diptheria , S.pneumonia
• Mycobacterium tuberculosis
– Significance, high risk populations
– Symptoms, pathology disease process
– Treatment & resistance
• Mycoplasma pneumonia
– symptoms & treatment, no cell wall hence Abiotic
choice
• Legionella,
– environmental risk, intracellular survival, Abiotics

Microbiology (30 decks)

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