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Microbiology > Mycobacterium Tuberculosis > Flashcards

Mycobacterium Tuberculosis Flashcards

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Biology 101 flashcards
1
Q

Describe the appearance/characteristics of mycobacterium

A

Rod shaped
Aerobic
ACID FAST

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2
Q

Where do mycobacterium like to replicate

A

Intracellularly within macrophages!

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3
Q

What are two deadly diseases that mycobacterium cause in humans?

A

TB and Leprosy

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4
Q

Why is culture not useful for TB or Leprosy?

A

Because mycobacterium is super slow growing since it has a waxy coating/coat of armor.

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5
Q

What populations is Atypical Mycobacteria almost exclusively seen in?

A

AIDs and HIV populations. Cause a TB like presentation in AIDs pts.

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6
Q

What are the two groups of Atypical Mycobacteria?

A

Fast growing atypical mycobacteria and Slow growing atypical mycobacteria.

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7
Q

What are the 2 important species to know in the slow growing atypical mycobacterium?

A

Avium Intracellulare (MAC complex) and Kansaii. Both cause pulmonary disease.

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8
Q

What are the important acid fast pathogens from this lecture?

A

Mycobacterium
Nocardia
Rhodococcus

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9
Q

What do the related acid fast pathogens have in common?

A

They are common in soil and water and may be transmitted from the environment, they cause chronic diseases via opportunistic infections in susceptible populations.

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10
Q

Describe the appearance of Nocardia species.

A

Long filamentous rods with branching.

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11
Q

Where do nocardia species like to grow and replicate

A

Intracellular growth within macrophages, similar to TB.

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12
Q

What histological/pathological finding is seen with nocardia? What unique complication is also seen?

A

Chronic lung abscess or granuloma that resembles TB. Unique complication is dissemination to the brain with abscesses.

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13
Q

Describe the appearance of the Rhodococcus species:

A

Short rods with coccie

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14
Q

What disease does the rhodococcus species cause?

A

Chronic lung disease in AIDs pts.

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15
Q

Describe the morphology of mycobacterium tuberculosis

A

Slender, straight, or pleomorphic curved rods. May form long serpentine cords (especially virulent), acid fast stain.

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16
Q

What are the growth requirements for mycobacterium tuberculosis

A

They are obligate aerobes, they take weeks to grow on agar media, and they are capable of intracellular growth within macrophages.

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17
Q

What are the virulence factors of mycobacterium tuberculosis?

A

peptidoglycans, NO LPS, cell wall glycolipids, cell membrane glycolipids, PPD protein

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18
Q

What makes the mycobacterium waxy?

A

The cell wall outer membrane glycolipids that contain mycelia acid.

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19
Q

How is mycobacterium tuberculosis transmitted?

A

Via person to person by inhalation of respiratory droplets, ingestion of unpasteurized milk/cheese, or direct contact with animals

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20
Q

Describe mycobacteria transmission in terms of survival.

A

It can survive drying for long periods. It can last on objects for hours.

21
Q

What % of the world is infected with TB?

A

ONE THIRD

22
Q

What populations have the highest rate of TB in the US

A

AIDs, homeless, elderly, those with compromised cell-mediated immunity.

23
Q

Is the primary infection symptomatic/asymptomatic, infectious/noninfectious?

A

Asymptomatic and non-infectious.

24
Q

What is happening with the mycobacteria during the primary infection?

A

there is intracellular multiplication within alveolar macrophages, there is spread to hilar lymph nodes, and there may be bloodstream dissemination with new foci in spleen, liver, (where there are lots of macrophages!)

25
Q

How are TB tubercles formed?

A

TB tubercles are a form of granulomatous inflammation. They are composed of epithelioid macrophages that contain viable replicating bacteria and they are surrounded by fibroblasts, macrophages, and lymphocytes.

26
Q

How does the body control TB?

A

Acquired cell mediated immunity in most individuals causes the primary infection to be asymptomatic and quiescent.

27
Q

Latent Infection of TB

A

This is when the TB is asymptomatic. There has been tubercle formation but the Cell Mediated Immunity of the body is in control and it is not causing any exacerbations yet.

28
Q

Secondary infection of TB: infectious/non-infectious, asymptomatic/symptomatic

A

Symptomatic and infectious!

29
Q

What is the pathogenesis of secondary TB infection?

A

There is renewed bacterial replication and the TB tubercles develop caseous centers which liquefy and empty into an adjacent bronchus. The viable organisms are released fro transmission to others.

30
Q

Symptoms of secondary TB:

A

indidious onset with fever, fatigue, anorexia, night sweats, wasting, cough and sputum in more advanced disease.

31
Q

How does the progression of TB differ in AIDs pts compared to non-immunocompromised puts?

A

The aids pt may never progress to latent infection. Since their CMI is low anyway they may go immediately to secondary/infectious and symptomatic stage.

32
Q

What is Miliary Tuberculosis

A

This is a life-threatening complication of TB.

33
Q

What is the pathogenesis of Miliary TB?

A

Bacteria get into the lymphatics and bloodstream and seed distant organs with small focal lesions.

34
Q

What is a common complication and cause of death with Miliary TB?

A

Meningitis.

35
Q

What is the best way to diagnose Mycobacterium TB?

A
  • Chest XR
  • Acid fast stain of sputum
  • Culture on special media (remember: slow growth!)
  • Nucleic acid amplification tests-used to confirm + AFB smear
  • Immune status/CMI responses
36
Q

What are 2 ways to test the CMI response/immune status?

A

PPD test and IFN-gamma release assay

37
Q

What does the PPD skin test detect?

A

latent and active infections.

38
Q

What does the IFN-gamma release assay detect?

A

latent and active infections.

39
Q

How is the IFN-gamma release assay performed?

A

Whole blood is mixed with TB antigens and the amount of IFN-gamma released from T cells is measured.

40
Q

What is the problem with doing a PPD skin test in HIV/AIDs pt?

A

They may show false negatives since their CMI is weak anyway

41
Q

1st line tx of TB

A

Isoniazid, Rifampin, Pyrazinamide, Ethambutol

42
Q

2nd line tx of TB

A

FQs, amikacin, kanamycin, capreomycin, ciomycin, cycloserine, ethionamide, p-aminosalicylic acid.

43
Q

What is the treatment regimen for TB?

A

4 drugs given for at least a 6 month period.

44
Q

MDR TB Definition:

A

Resistance to at least two of the 1st line drugs, one being isoniazid or rifampin

45
Q

XDR TB Definition

A

Resistance to 3 or more of the second line drugs including all of the FQs + one of the three injectable drugs (amikacin, kanamycin, or capreomycin).

46
Q

What does the WHO say is the most effective method of combating TB worldwide?

A

Direct observation therapy!

47
Q

Tx or MAC:

A

3 Drug therapy

Azithromycin + clarithromycin + rifabutin + ethambutol

48
Q

Prevention of TB

A
  • PPD skin testing in high risk groups/HCWs.
  • Isoniazid prophylaxis to prevent secondary infection in those already infected
  • BCG vaccine to prevent initial infection
  • Azithromycin + rifabutin prophylaxis in susceptible AIDs pt (prevents MAC)

Microbiology (13 decks)

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