Mycobacteria Flashcards
Mycobacteria are in the class of __________
Actinomycetes
Mycobacterium tuberculosis complex
Includes:
- M. tuberculosis
- M. bovis
- M. africanum
- M. microti
Non-tuberculos mycobacteria
Still causes disease, but not as severe
- classified based on growth rate and pigment production (Runyon group)
General characteristics
- 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
Growth requirements
Complex egg enriched media
- Dorset’s egg medium
- Lowenstein-Jensen agar
- Herrold’s egg yolk agar medium
What stain do you use for mycobacteria?
Acid-fast due to mycolic acid and WaxD
Cell wall structure
Mycolic acid, cord factor (lipoarabinomann, generated from trehalose dimycolate), and waxD (peptidoglycolipid)
What are the 3 causative agents of tuberculosis?
- humans: M. tuberculosis
- bovine: M. bovis
- avian: M. avium
- all 3 types may produce infection in host species other than their own*
M. bovis
- growth: Dorset’s egg medium without glycerol
- slow growing: 3-4 weeks
- transmission: inhalation
What was a major cause of human TB before the eradication program in 1924?
M. bovis
What reduced M. bovis infection?
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
M. bovis vaccine
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)
M. bovis pathogenesis
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
Primary complex
The primary focus plus similar lesions formed in the regional lymph node
M. bovis aerosol path of infection
Primary focus formation –> recognizable tubercle formed –> delayed type hypersensitivity (30 days) –> effective = cell mediated immunity
M. bovis clinical findings
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
Diagnostics
- postmortem: histopathologic exam
- antemortem: intradermal tubculin tests
- tests based on delayed type hypersensitivity, which develops 30 days after the infection*
What are the 4 official tuberculosis tests?
- 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
M. lepraemurium
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
M. leprae
Cause of leprosy in humans
- found in spontaneously occurring disease in armadillos
- is not grown on artificial medium
M. avium
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
M. avium subsp. paratuberculosis
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)
M. avium pathogenesis
- 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)
MAP in macrophage
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
