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