Category:Mycobacterium species

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  • Mycobacterial infections are caused by bacteria belonging to the family Mycobacteriaceae, order Actinomycetales
  • Includes obligate pathogens, opportunistic pathogens and saprophytes
  • Cause chronic, progressive, granulomatous infections
  • Cause tuberculosis, Johne's disease and feline leprosy
  • M. bovis, M. tuberculosis and M. avium cause tuberculosis of cattle, tuberculosis of pigs and tuberculosis of dogs respectively
  • The 'classical' tuberculosis lesions are caused by the Mycobacterium tuberculosis complex
  • The Johne's type lesions are caused by the Mycobacterium avium complex
  • Environmental species are found in soil, vegetation and water
  • Mycobacterium leprae and M.lepraemurium cause human, feline/murine leprosy respectively
  • Atypical mycobacteriosis is a localized opportunistic skin and subcutaneous infection caused by saprophytic and rapidly growing atypical mycobacteria
  • Granulomatous lesions in muscle and skin
  • Skin tuberculosis of cattle causes nodules along the lymphatics of the limbs
  • Bovine farcy is thought to be caused by M. senegalense and M. farcinogenes
  • Saprophytic mycobacteria cause granulomatous lesions


  • Aerobic, weakly Gram-positive acid-fast rods
  • Non-motile, non-spore forming
  • Cell walls contain mycolic acid
  • Require egg-based media for growth
  • Slow-growing colonies
  • 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


  • Identified by Ziehl-Neelson staining
  • Differentiated by culture, biochemical tests, chromatography and molecular techniques
  • Pathogenic species require at least three weeks for growth on egg-based media

Mycobacterium bovis

Mycobacterium avium

Feline leprosy

  • Caused by M. lepraemurium
  • Sporadic infections of cats via bites from infected rodents
  • Subcutaneous nodules form usually on the head or limbs and can ulcerate
  • Smears reveal Ziehl-Neelson-positive rods
  • Diagnosis by histopathology
  • Treatment includes excision of lesions

Johne's Disease (paratuberculosis)

  • Johne's Disease is a chronic, contagious enteritis of ruminants
  • Caused by M avium subsp. paratuberculosis
  • Epidemiology
    • Transmitted to young calves by ingestion of mycobacteria in faeces of infected adults
    • Organisms viable in environment for long periods
    • Long incubation period with clinical signs appearing in cattle over 2 years of age
    • Subclinical carriers can occur, shedding organisms in their faeces
  • Pathogenesis and pathogenicity
    • M avium subsp. paratuberculosis is an intracellular pathogen
    • Mycobacteria are ingested by macrophages in the Peyer's patches
    • Survival and replication of mycobacteria in macrophages initiate an immune-mediated granulomatous reaction
    • Lymphocytes and macrophages accumulate in the lamina propria and submucosa, resulting in marked thickening and folding of the intestinal wall
    • Mesenteric lymph nodes are enlarged
    • A protein-losing enteropathy results, along with failure to absorb nutrients and water
  • Clinical signs
    • Diarrhoea, initially intermittent, and weight loss in cattle
    • Weight loss in sheep and goats
    • Rapidly fatal with weight loss and diarrhoea in some deer
  • Diagnosis
    • All diagnostic procedures have faults but include:
    • Microscopy of rectal biopsies
    • Faecal culture
    • Serology of serum including complement fixation tests, agar-gel immunodiffusion test and an ELISA
    • Histopathology of intestines and lymph nodes
    • Isolation and identification of mycobacteria from faeces and tissues
    • Ziehl-Neelson-positive smears
    • Intradermal tuberculin test
    • DNA probes for detection in faeces
  • Control
    • Slaughter of affected animals
    • Detection and slaughter of subclinical shedders using faecal culture, DNA probes and ELISA
    • Good hygiene to protect young calves
    • Separation and isolation of calves from affected dams
    • Inactivated adjuvanted vaccines are available and reduce shedding of mycobacteria but do not eliminate infection

Pages in category "Mycobacterium species"

The following 4 pages are in this category, out of 4 total.