Lecture 23 Flashcards
What are the key features of a Mycobacteria?
- Thick cell
- Hydrophobic
- Waxy
Describe the living conditions of Mycobacteria
- Aerobic and nonmotile
- > some can grow under hypoxic conditions
- Free-living and parasites
- Fast and slow growing
Describe a Buruli Ulcer
- Necrotising infection of the skin and soft tissues
- Endemic in tropical regions
- Painless therefore often left untreated
- No vaccine, healed through antibiotics
What is M.Ulceran’s growth rate?
Slow
What is Mycolactone?
A virulence factor for M.Ulceran’s
Describe M.Ulceran’s host range
- Narrowed host range
- Specialised to humans and in particular the skin due to optimal heat conditions
What is an example of horizontal gene transfer in M.Ulceran’s?
Mycolactone, picked up a plasmid.
-Considered the key event in speciation of M.Ulceran’s/M.Marinum
Describe the reductive evolution in M.Ulceran’s when compared to M.Marinum
- Genomic size = smaller
- Pseudogenes = has more
- IS elements = has more
- PE and PPE = has less
- Secretion systems = some have been lost
What are the two functions of Mycolactone?
- Cytotoxin - host killing
2. Immunosuppressant - enables it to keep growing
What is the effect of high concentrations of Mycolactone?
Cytotoxic via apoptosis (local tissue destruction)
What is the effect of low concentrations of Mycolactone?
Immunosuppressant activity (invades the immune system)
When comparing M.U and M.M what is the homology?
High homology at the nucleotide level (98%)
What are IS elements responsible for in M.U?
- Rearrangements/deletions/insertions
2. Pseudogene formation via insertion (gene inactivation)
For deletion to occur, where does the reciprocal recombination need to occur?
Between direct repeat insertion sequence or Transposons
-Elements excise the DNA sequences between them
For inversion to occur, where does the reciprocal recombination need to occur?
Between Invert repeat insertion sequences or Transposons
-Elements inverts the DNA sequences between them
What are the causes of pseudogenes?
- Point mutations (insertions/deletions/substitutions)
2. Insertion events (e.g. Tn, IS element, prophage)
What are PE/PPE proteins?
Cell surface/secreted proteins with virulence and immune modulatory functions
Describe direct sunlight and M.M vs M.U and what this suggests
- There is a gene that produces a pigment allowing M.M to survive in direct sunlight
- In M.U this gene has a point mutation which leads to a premature stop codon
- Suggests that M.U ISN’T exposed to direct sunlight in natural habitat
What are ESX secretion systmes
They secrete proteins into host cells
Describe ESX in M.U and what this may account for
-2ESX systems are deleted which may account for extracellular pathology
What are ESX systems important for in M.TB?
- Virulence
- Intracellular spread
- Immunomodulation
