Lecture 29 - Mycobacterial Infections II Flashcards Preview

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Flashcards in Lecture 29 - Mycobacterial Infections II Deck (37):
1

Names for ulcer caused by M ulcerans

Bairnsdale ulcer
Buruli ulcer

2

How was M ulcerans isolated from Bairnsdale ulcers?

Bacteriologists from the Alfred Hospital in Melbourne used a faulty incubator to incubate samples (couldn't maintain 37C)

3

Optimal temperature at which M ulcerans grows

30C

4

Countries most affected by M ulcerans

Western and Central Aftrican nations
Mostly tropical regions

5

Number of M ulcerans cases in West Africa since 2000

Over 10,000

6

Demographic most affected by M ulcerans

Young children

7

M ulcerans treatment

Responds to combination therapy
Streptomycin, rifampicin for 8 weeks
No vaccine

8

M ulcernas mortality and morbidity

Doesn't kill, but advanced cases can require surgery

9

M ulcerans epidemiology
1)
2)
3)

1) Very local epidemiology
2) Transmission appears to be from environment to humans (often aquatic environment)
3) Not human-human transmission

10

Point Lonsdale M ulcerans epidemic
1)
2)
3)

1) 3000 permanent residents
2) More than 90 cases since 2002
3) Nearby Queenscliff unaffected for a long time

11

M ulcerans pathology
1)
2)
3)
4)
5)

1) Prominent subcutaneous necrosis
2) Dermal layer of skin remains intact, tissue below dermis becomes encrotic
3) Ulcers of skin often painless
4) Granulomas often only form when ulcer begins to heal
5) An extracellular infection

12

Toxin produced by M ulcerans

Mycolactone

13

Mycolactone
1)
2)
3)
4)

1) A lipid toxin
2) Small, polyketide
3) Potent immunosuppressor at low concentrations
4) Cytotoxic at higher concentrations

14

Mycolactone- M ulcerans mutants

Avirulent

15

Pre-ulcerative lesion
1)
2)
3)
4)
5)

1) Small, movable nodule
2) Small bacterial load
3) Little tissue necrosis
4) Subcellular localisation
5) High local inflammatory response (IFNg)

16

Ulcerative lesion
1)
2)
3)
4)

1) High bacterial load
2) Lots of extracellular bacteria
3) Extensive tissue necrosis
4) Impaired local inflammatory response from mycolactone release

17

Spontaneous healing or treatment of M ulcerans
1)
2)
3)
4)

1) Bacterial load decreases
2) Subcellular localisation
3) Reduced tissue necrosis
4) Local inflammatory response returns, with reduced levels of mycolactone
5) Granuloma formation

18

Mycolactone structure

Macrolactone ring with two acyl sidechains

19

M ulcerans doubling time

50 hours

20

What is M ulcerans most closely related to?

M marinum (based on 16S RNA comparison)

21

M ulcerans genome
1)
2)
3)
4)

1) 5.6MB circular genome
2) 174kb megaplasmid (pMUM001)
3) 304 copies of 2 insertion sequences
4) 771 pseudogenes

22

pMUM001
1)
2)
3)

1) 174kb megaplasmid in M ulcerans
2) Contains genes for mycolactone synthesis
3) 81 genes
4) 3 extremely large genes

23

pMUM001 very large genes
1)
2)
3)

1) mlsA1 (51kb)
2) mlsA2 (43kb)
3) mlsB (7kb)

24

What do mlsA1, mlsA2 and mlsB encode?

Encode polyketide synthases (multi-enzyme complexes) that synthesise mycolactone

25

Mycolactone polyketide synthase
1)
2)
3)
4)

1) Produce lipids by sequential addition of acetate or propionate
2) Genes are divided into modules. Each module adds an acetate or propionate onto chain
3) The more modules there are, the longer the final polyketide will be.
4) mlsA1 and mlsA2 make the macrolactone ring (spontaneous cyclisation) and one acyl chain, mlsB makes the other acyl chain. An enzyme joins the two together

26

Effect of mycolactone on the immune system

Suppresses IL-2 secretion by T cells

27

Do different M ulcerans strains make different mycolactone?

Yes

28

Most potent mycolactone strain

A/B (inhibits IL-2 synthesis at the smallest concentration)

29

How similar are homologous modules of mlsA1, mlsA2 and mlsB in different strains of M ulcerans?

Over 98% nucleotide identity between domains of the same function

30

How could mycolactone polyketide synthase be used to develop drugs?

Substitute in different modules to produce drug of interest.
Good idea, but very hard to execute

31

Similarities between M ulcerans, B pertussis and Y pestis
1)
2)
3)
4)
5)

1) Plague, whooping cough pathogens have many pseudogenes
2) Evidence of lateral gene transfer
3) Closely related to a non-pathogenic species
4) Many insertion sequences
5) Reduced genome compared to close, non-pathogenic relative

32

Implication of similarities between M ulcerans, B pertussis and Y pestis

All bacteria have evolved recently to adapt to a new environment, niche

33

Differences between M ulcerans and M marinum
1)
2)
3)
4)

M ulcerans has:
1) Reduced phospholipase C repertoire
2) Fewer glycoproteins
3) No phenolic glycolipids
4) Mycolactone-rich vesicles and cell membrane

34

How were mosquitoes found to contain M ulcerans in Point Lonsdale?
1)
2)
3)

1) Aedes notoscriptus larvae exposed to tap water with possum faeces contamination (possum faeces contains M ulcerans)
2) Water changed, tested every instar with Taqman PCR
3) Mosquito larvae tested at each instar, and as adult, with Taqman PCR

35

Results of experiment with Aedes notoscriptus larvae?

M ulcerans persists within mosquito larvae
In midgut, mouthparts
M marinum does not do this

36

Animals in Point Lonsdale that act as a reservoir for M ulcerans

Mosquitoes, possums

37

Animal reservoir in Africa for M ulcerans

Not found yet in mosquitoes, obvious animals