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Infectious Agents > Mycobacteria > Flashcards

Mycobacteria Flashcards

1
Q

Mycobacteria are in the class of __________

A

Actinomycetes

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2
Q

Mycobacterium tuberculosis complex

A

Includes:

  • M. tuberculosis
  • M. bovis
  • M. africanum
  • M. microti
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3
Q

Non-tuberculos mycobacteria

A

Still causes disease, but not as severe

- classified based on growth rate and pigment production (Runyon group)

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4
Q

General characteristics

A
  • obligate aerobic, non-spore forming, non-motile
  • fastidious growth
  • intracellular parasite that targets macrophages
  • resistant to dehydration, acid, alkali, chemical disinfectants, antibiotics, and environmental factors
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5
Q

Growth requirements

A

Complex egg enriched media

  • Dorset’s egg medium
  • Lowenstein-Jensen agar
  • Herrold’s egg yolk agar medium
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6
Q

What stain do you use for mycobacteria?

A

Acid-fast due to mycolic acid and WaxD

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7
Q

Cell wall structure

A

Mycolic acid, cord factor (lipoarabinomann, generated from trehalose dimycolate), and waxD (peptidoglycolipid)

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8
Q

What are the 3 causative agents of tuberculosis?

A
  • humans: M. tuberculosis
  • bovine: M. bovis
  • avian: M. avium
  • all 3 types may produce infection in host species other than their own*
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9
Q

M. bovis

A
  • growth: Dorset’s egg medium without glycerol
  • slow growing: 3-4 weeks
  • transmission: inhalation
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10
Q

What was a major cause of human TB before the eradication program in 1924?

A

M. bovis

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11
Q

What reduced M. bovis infection?

A

Milk pasteruization and slaughtering all tuberculin skin test positive animals

  • reduced infection from 5% in 1917 to less than 0.001%
  • Mexican cattle are commonly infected
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12
Q

M. bovis vaccine

A

Attenuated live

  • bacillus calmette-guerin (BCG)
  • federal law prohibits use of BCG in US –> cannot discriminate naturally infected from vaccinated (skin test is positive in both populations)
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13
Q

M. bovis pathogenesis

A

Inhaled bacilli are phagocytosed by alveolar macrophages –> either clear the infection or allow mycobacteria to proliferate

  • primary focus forms due to proliferation mediated by cytokines associated with a hypersensitivity rxn
  • purulent to caseous, necrotic center may calcify and lesion may become surrounded by granulation tissue and a fibrous capsule to form the classic tubercle
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14
Q

Primary complex

A

The primary focus plus similar lesions formed in the regional lymph node

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15
Q

M. bovis aerosol path of infection

A

Primary focus formation –> recognizable tubercle formed –> delayed type hypersensitivity (30 days) –> effective = cell mediated immunity

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16
Q

M. bovis clinical findings

A

Clinical signs are only evident in advanced disease

  • generalized signs: emaciation, lethargy, weakness, anorexia, fever
  • bronchopneumonia in respiratory form of disease
  • superficial lymph node enlargement
17
Q

Diagnostics

A
  • postmortem: histopathologic exam
  • antemortem: intradermal tubculin tests
  • tests based on delayed type hypersensitivity, which develops 30 days after the infection*
18
Q

What are the 4 official tuberculosis tests?

A
  • caudal fold tuberculin test
  • cervical tuberculin test
  • comparative cervical tuberculin test
  • bovine interferon gamma assay (cattle only) –> blood samples collected between 3-30 days after injection of bovine tuberculin for CFT
19
Q

M. lepraemurium

A

Non-photochromogenic, slow growing, acid-fast bacillus

  • grown on media with cytochrome C and alpha-ketoglutarate
  • causative agent of feline leprosy
  • transmitted thru bites
  • surgical excision of lesion
20
Q

M. leprae

A

Cause of leprosy in humans

  • found in spontaneously occurring disease in armadillos
  • is not grown on artificial medium
21
Q

M. avium

A

Ubiquitous in the environment

  • produces disease primarily in birds (natural host)
  • serotypes 1, 2, and 3 are more virulent in birds
  • serotypes 4-21 cause generalized disease in domestic animals
  • infected chickens: irregular gray-yellow or gray-white nodules in liver, spleen, intestine
  • infected swine: granulomatous lesions in mesenteric and mandibular lymph nodes
  • virulent in HIV patients
22
Q

M. avium subsp. paratuberculosis

A

Causative agent of Johne’s disease

  • chronic debilitating enteritis in ruminants
  • grows more slowly than other mycobacteria (6-8 weeks)
  • rough colonies on Middlebrook agar medium
  • in vitro growth requires iron-transport compound (mycobactin J)
  • obligate parasitic pathogen (requires iron)
  • extremely hardy and may remain in contaminated soil and water for 1 yr or more by developing extra tough outer coat (mycolic acid)
23
Q

M. avium pathogenesis

A
  • transmission: fecal oral route
  • site of infection: ileum
  • invades thru Peyer’s patches via M cell to macrophage
  • infection may be dormant for years before clinical signs (animal becomes a reservoir)
24
Q

MAP in macrophage

A

Inhibits phagosome maturation and downregulates MHC expression –> triggers host inflammation via cell mediated immune response –> MAP spreads to mesenteric lymph nodes becoming systemic
= clinical signs include persistant diarrhea, and weight loss

25
Q

MAP diagnosis

A

Test adult animal ( at least 18 mo old )

  • young animals do not shed, or produce antibodies
  • fecal culture: any species approved by USDA
26
Q

Serologic test

A

ELISA approved by USDA

  • cattle, sheep, goat
  • sensitivity correlated with stage of disease
27
Q

Gene probe/PCR

A

Approved by USDA

  • rapid, and accurate results
  • only pathogen approved for PCR
28
Q

Treatment and prevention of MAP

A

No treatment for Johne’s disease

  • vaccine is not a solution, causes false positive rxn to TB skin test
  • control and eradication: USDA sponsored voluntary eradication program is implemented –> ID and culling of infected shedders, removing calves from dams immediately after birth and feeding with colostrum free of MAP

Infectious Agents (44 decks)

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