Lecture 29 - Mycobacterial Infections II Flashcards
Names for ulcer caused by M ulcerans
Bairnsdale ulcer
Buruli ulcer
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)
Optimal temperature at which M ulcerans grows
30C
Countries most affected by M ulcerans
Western and Central Aftrican nations
Mostly tropical regions
Number of M ulcerans cases in West Africa since 2000
Over 10,000
Demographic most affected by M ulcerans
Young children
M ulcerans treatment
Responds to combination therapy
Streptomycin, rifampicin for 8 weeks
No vaccine
M ulcernas mortality and morbidity
Doesn’t kill, but advanced cases can require surgery
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
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
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
Toxin produced by M ulcerans
Mycolactone
Mycolactone 1) 2) 3) 4)
1) A lipid toxin
2) Small, polyketide
3) Potent immunosuppressor at low concentrations
4) Cytotoxic at higher concentrations
Mycolactone- M ulcerans mutants
Avirulent
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)
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
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
Mycolactone structure
Macrolactone ring with two acyl sidechains
M ulcerans doubling time
50 hours
What is M ulcerans most closely related to?
M marinum (based on 16S RNA comparison)
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
pMUM001
1)
2)
3)
1) 174kb megaplasmid in M ulcerans
2) Contains genes for mycolactone synthesis
3) 81 genes
4) 3 extremely large genes
pMUM001 very large genes
1)
2)
3)
1) mlsA1 (51kb)
2) mlsA2 (43kb)
3) mlsB (7kb)
What do mlsA1, mlsA2 and mlsB encode?
Encode polyketide synthases (multi-enzyme complexes) that synthesise mycolactone
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
Effect of mycolactone on the immune system
Suppresses IL-2 secretion by T cells
Do different M ulcerans strains make different mycolactone?
Yes
Most potent mycolactone strain
A/B (inhibits IL-2 synthesis at the smallest concentration)
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
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
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
Implication of similarities between M ulcerans, B pertussis and Y pestis
All bacteria have evolved recently to adapt to a new environment, niche
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
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
Results of experiment with Aedes notoscriptus larvae?
M ulcerans persists within mosquito larvae
In midgut, mouthparts
M marinum does not do this
Animals in Point Lonsdale that act as a reservoir for M ulcerans
Mosquitoes, possums
Animal reservoir in Africa for M ulcerans
Not found yet in mosquitoes, obvious animals
