Mycobacteria Flashcards
Genotypic analysis methods
- DNA based: Genomic content (G+C)
- DNA-DNA hybridisation
- Ribosomal rRNA sequences
- MLST
- Whole genome
What is phenotype?
Physical characteristics including:
- cell morphology and
- stains that you use
- Oxygen requirements
- . Culture properties
- Colonial morphology
- Biochemical reactions
name 3 stains
Gram positive, Gram negative and acid fast
Difference between gram positive and negative xxxxxxxxxxxxxx 17 mins
!. gram positive = no outside cell wall
2. Gram negative = outer membrane
What are the phenotypic characteristics of mycobacteria?
- Aerobic
- Non-spore forming & non-motile,
- Rod shaped/bacilli,
- Acid-Fast
- Require complex egg-enriched media for growth of pathogenic species
- Pathogenic species grow slowly, colonies only visible after several weeks.
- Major diseases include tuberculosis and Johne’s disease (a GI disease)
Why are they acid fast not gram pos/ neg
more like gram negative but doesn’t stain very well with either gram neg or positive = acid fast
What are the typical habitats of mycobacterium?
- Lipid rich walls make mycobacteria hydrophobic
- This allows resistance to adverse environments
- Environmental bacteria found in soil, vegetation and in water sources
4 . Mycobacteria that are ‘obligate pathogens’ are shed by infected animals - After shedding they can survive in the environment for extended periods (several months)
- Mycobacterial disease in animals is chronic and progressive
- Considerable degree of host specificity in disease niches
What is the term used for acid fast staining
Ziel-Neelsen (ZN)
How can Mycobacterium bovis be transmitted?
- Transmission through aerosols created from cattle
- Risk factors for transmission include housing and wildlife reservoirs (possums/badgers)
- Calves infected by ingesting contaminated milk
- Pasteurisation of milk greatly reduced human exposure
What is the main pathogensis mechanism for mycobacterium bovis?
- Relates to the ability to survive and multiply in host macrophages
- Macrophages accumulate at infection site is response to presence of cell wall waxes and lipids
- Granuloma formation = inflammatory response in lungs
- Recognizable tubercle formed (inflammatory tissue)
What are the clinical signs of mycobacterium bovis?
- Only present in advanced disease.
- Cattle with extensive lesions may still appear in good health.
- In advanced plumonary TB animals develop cough /intermittent pyrexia.
- Infection of mammary tissue causes lymph node enlargement & mastitis increases spread.
Diagnosis of mycobacterium bovis
Tuberculin test:
- Standard ante-mortem test (before death)
- Usually reactive 30-50 days after infection
- Delayed type hyper-sensitivity to M. bovis tuberculoprotein (‘tuberculin’)
- Purified protein derivative (PPD) is injected intradermally
- PPD injected and site checked a few days later
- Some other tests used in conjunction e.g. ELISA
- If animal dies pathology and staining (ZN) of tissue section thought to be tubercle locations
- Isolation of bacteria to characterise = Commercial kits
Current control mechanisms. What about antibiotics and vaccinations?
- treatment of antibiotics = saved for human
- Vaccination = once vacciens = can’t discriminate between reactors becuase some will show positive to the test
- sooo tuberculin testing, isolation, slaughter of reactors
- Culling wildlife
- Routine meat inspection part of surveillance
What is human TB caused by?
How can it be transmitted
Lung disease
Mycobacterium tuberculosis
- highly contagious
- successful antibiotic but not used with animals due to resistance fear
Mycobacterium Lepraemurium
Skin Disease
- Feline leprosy
- Transmission through bites
- Endemic in rodents in some parts
- not zoonotic
- Lesions
