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===Overview===
===Overview===
*Mycobacterial infections are caused by bacteria belonging to the family Mycobacteriaceae, order Actinomycetales
*Includes obligate pathogens, opportunistic pathogens and saprophytes
*Includes obligate pathogens, opportunistic pathogens and saprophytes
*Cause chronic, progressive, granulomatous infections
*Cause chronic, progressive, granulomatous infections
*Cause tuberculosis, Johne's disease and feline leprosy
*Cause tuberculosis, Johne's disease and feline leprosy
*''M. bovis'', ''M. tuberculosis'' and ''M. avium'' cause [[Respiratory Bacterial Infections - Pathology#Tuberculosis|tuberculosis of cattle]], [[Respiratory Bacterial Infections - Pathology#Tuberculosis in pigs|tuberculosis of pigs]] and [[Respiratory Bacterial Infections - Pathology#Tuberculosis in dogs|tuberculosis of dogs]] respectively
*Environmental species found in soil, vegetation and water
*Environmental species found in soil, vegetation and water
===Characteristics===
===Characteristics===
*Aerobic acid-fast rods
*Aerobic, weakly Gram-positive acid-fast rods
*Non-motile, non-spore forming
*Non-motile, non-spore forming
*Cell walls contain mycolic acid
*Cell walls contain mycolic acid
*Slow-growing colonies
*Slow-growing colonies
*Resistant to disinfectants and environmental conditions; susceptible to pasteurisation
*Resistant to disinfectants and environmental conditions; susceptible to pasteurisation
*Mycobacteria stain with carbol dyes and resist subsequent decolorization with inorganic acids; this characteristic which is due to the spatial arrangement of mycolic acids within the cell wall makes them acid fast
*Pathogenesis and pathogenicity
*Pathogenesis and pathogenicity
**The ability of mycobacteria to survive and multiply within macrophages determines whether disease will occur within the host
**Survival and multiplication in macrophages at primary site of infection due to prevention of phagosome-lysosome fusion
**Survival and multiplication in macrophages at primary site of infection due to prevention of phagosome-lysosome fusion
**Mycobacteria utilize several virulence factors including cord factor or trehalose dimycolate, surface glycolipid, sulfatides, lipoarabinomannan, heteropolysaccharide, heat shock protein, complement, and tubuloprotein
**The types of immune responses that are critical in responding to mycobacterial infection are cell-mediated immunity and the delayed hypersensitivity response
**Pathogenicity of mycobacteria depends on their ability to escape phagocytic killing
**Mostly imparted by the cell wall consitiutents
***Cord factor (trehalose dimycolate) – surface glycolipid responsible for serpentine growth in vitro
***Suphatides – surface glycolipid containing sulphur which prevents fusion of phagosome with lysosome. cAMP secreted by the bacteria may also facilitate this. Also something about the cholesterol content of the phagosome….. nature article
***LAM – heteropolysaccharide which inhibits macrophage activation by IFNγ and induces macrophages to secrete TNFα -induces fever, etc and IL-10 which suppresses mycobacteria-induced T cell proliferation
***The wax of the cell wall, peptidoglycans and other glycolipids are responsible for the adjuvant activity – attracts APCs
***Tubuloprotein – important Ag, purified tubuloprotein is the basis of the tuberculin test
**Mycobacteria are released from macrophages and also migrate within macrophages around the body
**Mycobacteria are released from macrophages and also migrate within macrophages around the body
**Waxy cell wall contributes to the host immune response to the mycobacteria and the development of lesions
**Waxy cell wall contributes to the host immune response to the mycobacteria and the development of lesions
==Four major disease groups are recognised:==
==Four major disease groups are recognised:==