Mycobacterium (Ex3) Flashcards
Mycobacterium general features
- mycolic acid
- rod shaped
- weak gram positive staining
- aerobic
- survives well in environment
- survives inside macrophages
Virulence factors of Mycobacterium
mycolic acid containing cell wall lipids
- facilitate survival in macrophages
- stimulate cytokine production
- enhance immunomodulating effects
Cell protein antigens
- tuberculine
What diseases are caused by mycobacterium?
- mammalian tuberculosis
- avian tuberculosis
- leprosy
- Johne’s disease
Tuberculosis
- transmission and uptake
- main immune response
- inhalation and ingestion
- local multiplication, uptake by macrophages, migration to lymph nodes, lymphadenitis
- th1 response with gamma interferon production, macrophage activation, and killing of bacteria
- formation of tubercle: chronic granulomatous inflammation
Tuberculosis pathogenesis
- infected macrophages killed following release of cytotoxins and enzymes, leading to tissue destruction
- enzymatic action results in caseous necrosis and mineralization
- rupture of granulomas allows dissemination
Describe tuberculosis lesions
Tubercles are classic lesion:
- well-organized granulomas with central areas of epithelioid macrophages or caseous necrosis, surrounded by epithelioid cells and multinucleated giant cells
- rim of lymphocytes and fibrous connective tissue
M. Tuberculosis hosts
- humans are the main reservoirs
- dogs, cats, pigs, primates
- psittacine birds and canaries
- elephant to human transmission
M. bovis
- disease caused
- transmission
- zoonotic tuberculosis
- ingestion, inhalation, or by contact with mucus membranes and broken skin
- GI tract is the main portal of entry
- aerosol most common in cattle
- may be shed in milk
Clinical signs and lesions of M. bovis
- often sub clinical
- enlarged regional lymph nodes and cachexia seen in advanced stages
- pulmonary forms may have chronic cough
- late stages: firm nodular lesions on target organs and lymph nodes
What is the Caudal Fold Tuberculin Test?
screening test in caudal tail fold with single-strength dose of M. bovis purified protein derivative
What is the Comparative Cervical Tuberculin Skin Test?
paired cervical tests with double strength M. bovis and M. avium purified protein derivative in separate areas of the neck to rule out cross reaction with M. avium
Johne’s Disease
- bacteria
- type of disease
- hosts
- Mycobacterium avium subsp paratuberculosis
- chronic, progressive granulomatous enteritis
- primary hosts are ruminants, especially cattle
Pathogenesis and clinical signs of Johne’s disease
- infection through ingestion of contaminated material, milk, or in-utero
- localizes in macrophages in intestines and lymph nodes
- develop granulomatous enteritis, and cachexia
- CS: diarrhea and weight loss, granulomatous proliferation of ileo-cecal mucosa, most are asymptomatic shedders
Mycobacterium avium complex
- what does it include
- infection caused
- habitat
- M. intracellulare
- M. avium subsp avium: avian TB
- M. avium subsp sylvaticum: non-TB
- M. avium subsp hominisuis: pigs and humans
- causes opportunistic granulomatous infections in humans and animals
- widespread in soil and water
Mycobacterium ulcerans
- disease caused
- habitat
- causes Buruli ulcer
- a frequent disease in humans
- cytotoxin, mycolactone, causes tissue necrosis
- in tropical wetlands
