Lecture 23

Question 1

What are the key features of a Mycobacteria?

Answer 1

• Thick cell
• Hydrophobic
• Waxy

Question 2

Describe the living conditions of Mycobacteria

Answer 2

• Aerobic and nonmotile
• > some can grow under hypoxic conditions
• Free-living and parasites
• Fast and slow growing

Question 3

Describe a Buruli Ulcer

Answer 3

• Necrotising infection of the skin and soft tissues
• Endemic in tropical regions
• Painless therefore often left untreated
• No vaccine, healed through antibiotics

Question 4

What is M.Ulceran’s growth rate?

Answer 4

Slow

Question 5

What is Mycolactone?

Answer 5

A virulence factor for M.Ulceran’s

Question 6

Describe M.Ulceran’s host range

Answer 6

• Narrowed host range

- Specialised to humans and in particular the skin due to optimal heat conditions

Question 7

What is an example of horizontal gene transfer in M.Ulceran’s?

Answer 7

Mycolactone, picked up a plasmid.

-Considered the key event in speciation of M.Ulceran’s/M.Marinum

Question 8

Describe the reductive evolution in M.Ulceran’s when compared to M.Marinum

Answer 8

• Genomic size = smaller
• Pseudogenes = has more
• IS elements = has more
• PE and PPE = has less
• Secretion systems = some have been lost

Question 9

What are the two functions of Mycolactone?

Answer 9

1. Cytotoxin - host killing

2. Immunosuppressant - enables it to keep growing

Question 10

What is the effect of high concentrations of Mycolactone?

Answer 10

Cytotoxic via apoptosis (local tissue destruction)

Question 11

What is the effect of low concentrations of Mycolactone?

Answer 11

Immunosuppressant activity (invades the immune system)

Question 12

When comparing M.U and M.M what is the homology?

Answer 12

High homology at the nucleotide level (98%)

Question 13

What are IS elements responsible for in M.U?

Answer 13

1. Rearrangements/deletions/insertions

2. Pseudogene formation via insertion (gene inactivation)

Question 14

For deletion to occur, where does the reciprocal recombination need to occur?

Answer 14

Between direct repeat insertion sequence or Transposons

-Elements excise the DNA sequences between them

Question 15

For inversion to occur, where does the reciprocal recombination need to occur?

Answer 15

Between Invert repeat insertion sequences or Transposons

-Elements inverts the DNA sequences between them

Question 16

What are the causes of pseudogenes?

Answer 16

1. Point mutations (insertions/deletions/substitutions)

2. Insertion events (e.g. Tn, IS element, prophage)

Question 17

What are PE/PPE proteins?

Answer 17

Cell surface/secreted proteins with virulence and immune modulatory functions

Question 18

Describe direct sunlight and M.M vs M.U and what this suggests

Answer 18

• 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

Question 19

What are ESX secretion systmes

Answer 19

They secrete proteins into host cells

Question 20

Describe ESX in M.U and what this may account for

Answer 20

-2ESX systems are deleted which may account for extracellular pathology

Question 21

What are ESX systems important for in M.TB?

Answer 21

• Virulence
• Intracellular spread
• Immunomodulation