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BacT exam 3 > Mycobacterium > Flashcards

Mycobacterium Flashcards

1
Q

Staining characteristics of Mycobacterium sp.

A

Weak gram positive staining rods
Acid fast positive staining rods
Large amounts of lipids (mycolic acids) in the cell wall

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2
Q

The type of pathogen Mycobacterium sp. are

A

Facultative intracellular pathogens
Survive inside macrophages
Immunity is cellular (Th1 response)

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3
Q

Type of inflammatory response produced by Mycobacterium sp.

A

Cause granulomatous inflammation

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4
Q

Virulence factors of Mycobacterium sp.

A

Mycolic acid containing cell wall lipids - facilitate survival in macrophages (facultative intracellular pathogens)
Cell protein antigens - Tuberculin (purified protein derivative)

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5
Q

Important diseases caused by Mycobacterium sp.

A

Mammalian tuberculosis = M. tuberculosis complex - M. tuberculosis, M. bovis, M. africanum, M. microti
Avian tuberculosis = M. avium subsp. Avium serotypes 1-3
Leprosy = M. leprae (human), M. lepraemurium (cat)
Johne’s Disease = M. avium subsp. paratuberculosis

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6
Q

Tuberculous Group of Mycobacterium

A

Forms caseous granuloma
M. tuberculosis
M. bovis

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7
Q

Non-tuberculous Group of Mycobacterium

A

Forms non-caseous granuloma

M. avium complex

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8
Q

Pathogenesis of Tuberculosis

A

Infection (inhalation or ingestion) -> disease -> innate control -> spontaneous healing or containment in the body (latency) -> reactivation and disease transmission

Cell mediated immune response is important in the destruction of bacilli
If the bacilli survive, infected macrophages are killed following release of macrophage-derived cytotoxins and enzymes (Type IV hypersensitivity or Delayed type hypersensitivity)

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9
Q

Tuberculosis lesions

A

Tubercles are the classic lesion of tuerculosis
Granulomas with central areas of either solidly packed epithelioid macrophages (hard tubercle) or caseous necorsis (soft tubercle) surrounded by epithelioid cells and multinucleated giant cells (Langerhan’s cells)

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10
Q

Elements of a tubercle

A 
Activated macrophage/epithelioid cells
Lymphocytes
Fibrosis (fibroblasts/collagen)
Mineralization may occur
Coagulative/caseous/liquefactive necrosis may be present
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11
Q

Mycobacterium tuberculosis hosts

A

Humans are the main reservoir
Can infect dogs, cats, pigs, nonhuman primates
Psittacine birds and canaries are susceptible

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12
Q

Diagnosing Mycobacterium tuberculosis

A

Diagnositc imagin
Tuberculin testing (Mantoux testing)
TB is a treatable and curable disease

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13
Q

Anti-tubercular Drugs

A

Drugs are always used in combinations to treat tuberculosis
Primary Drugs - Isoniazid, Rifamycins, Ethambutol, Pyrazinamide
Secondary Drugs - Aminoglycosides, Fluoroquinolones

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14
Q

Problems with TB treatment

A

Combination drug therapy is needed
Need prolonged treatment
Poor drug distribution in walled off lesions
Multidrug Resistant TB (MDR) = resistant to isoniazid and rifampin
Extensively drug resistant TB (XDR) = resistant to isoniazid and rifampin, fluoroquinolones and at least one of three injectable second-line drugs

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15
Q

Mycobacterium bovis hosts

A

Widest host range of all TB organisms

Maintained primarily in bovine species

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16
Q

Mycobacterium bovis pathogenesis

A

GI tract is the main portal of entry
Chronic progressive, and latent infections
Disease is seldom apparent until it has reached advanced stages
Organisms can remain dormant in the body for lifetime without causing progressive disease

Causes disease indistinguishable from that of Mycobacterium tuberculosis of humans

17
Q

Mycobacterium bovis lesions

A

Advanced disease = enlarged regional lymph nodes and generalized wasting (cachexia)
Early stages = lesions are difficult to find at necropsy
Later stages = nodular lesions in target organs and associated lymph nodes

18
Q

Diagnosis of Mycobacterium bovis

A

Tuberculin hypersensitivity skin tests

  • screening test in caudal tail fold with single-strength dose of M. bovis purified protein derivative (PPD)
  • reactors in screening test are subsequently tested by paired cervical tests with double strength M. bovis PPD and M. avium PPD in separate areas of the neck to rule out cross reactions with M. avium subsp. paratuberculosis
19
Q

Mycobacterium avium subsp. paratuberculosis

  • disease names
  • type of disease
A

Johne’s disease, or paratuberculosis

A chronic progressive granulomatous enteritis

20
Q

Mycobacterium avium subsp. paratuberculosis hosts

A

Primary hosts = ruminants (cattle)

Young animals are most susceptible to infection with an incubation period up to two years before symptoms appear

21
Q

Pathogenesis of Mycobacterium avium subsp. paratuberculosis in cattle

A

Infection through ingestion of contaminated milk or in-utero
Localizes in macrophages in the intestine, local lymph nodes
Animal will either clear the infection, or delayed progression to disease
Develops granulomatous enteritis, cachexia (wasting of the body)
“Iceberg Effect” - numerous asymptomatic shedders

22
Q

Diagnosis of Mycobacterium avium subsp. paratuberculosis

A

Detection of Host Response to Infection:
Humoral immune response - ELISA or Agar gel immunodiffusion test used for herd testing when there have been prior cases or high infection prevalence in herd
Cell mediated immune response - Johnin hypersensitivity skin test; Interferon Gamma Release Assays (IGRA) or Lymphoblast Stimulation Assays

23
Q

Johne’s ELISA

A

Widely used in cattle herd to detect animals infected with Mycobacterium avium subsp. paratuberculosis
Detect humoral immune response to MAP
Low sensitivity in early stages of diseases
False positives can occur (specificity issues)

False negative results in advanced stages of disease due to mechanism called anergy

24
Q

Mycobacterium avium complex (MAC)

A

Opportunistic granulomatous infections in humans, animals, and birds
Widespread in soil and water, including treated municipal tap water

25
Q

Mycobacterium ulcerans

A

Causes Buruli Ulcer, a mysterious devastating disease

26
Q

Mycobacterium leprae

  • disease names
  • disease caused
A

Leprosy or Hansen’s Disease
Chronic granulomatous debilitating disease
Anaesthetic skin lesions, peripheral neuropathy, and nerve thickening

27
Q

Mycobacterium leprae transmission

A

Transmission from shedding through nose, not from skin

Animal reservoir = Nine banded Armadillo in southern United States

28
Q

2 types of Mycobacterium leprae leprosy

A

Tuberculoid leprosy - paucibacillary

  • paucibacillary = few AFB+ in the lesion
  • few acid fast positive bacilli in the lesion

Lepromatous leprosy - multibacillary

  • multibacillary = numerous AFB+ in the lesion
  • no cell mediated reponse, sever disease with numerous aid fast positive bacilli
29
Q

Mycobacterium lepraemurium

  • disease names
  • disease caused
A

Feline and Murine Leprosy
Solitary to multiple cutaneous nodules or ulcerated lesions
Granulomatous Dermatitis Panniculitis

30
Q

Diagnosis of Mycobacterium lepraemurium

A

Geimsa or Acid Fast Staining

In Geimsa or Gram stain-Negative stained (not Gram negative) bacilli are generally observed

BacT exam 3 (10 decks)

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