Difference between revisions of "Category:Mycobacterium species"

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Overview

• 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

Characteristics

• 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

Identification

• 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

Mycobacterium lepraemurium

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