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
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.