Mycobacteria spp.
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General Mycobacteria
- Mycobacterial infections are caused by bacteria belonging to the family Mycobacteriaceae, order Actinomycetales.
- Mycobacterium sp. are aerobic, weakly gram-positive, non-spore forming, non-motile bacilli with wide variations in host affinity.
- 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.
- The ability of mycobacteria to survive and multiply within macrophages determines whether disease will occur within the host.
- Mycobacteria sp. 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.
Four major disease groups are recognised:
- The 'classical' tuberculosis lesions are caused by the Mycobacterium tuberculosis complex
- The Johne's type lesions and lesions caused by the MAC (M.avium complex) are Mycobacterium avium complex
- Mycobacteria causing leprosy (human and feline/murine) Mycobacterium leprae and M.lepraemurium
- Atypical mycobacteriosis is a localized opportunistic skin and subcutaneous infection caused by saprophytic and rapidly growing mycobacteria Atypical Mycobacterium