Lecture 28 - Mycobacterial Infections Flashcards
Acid fast
A stain.
Based on how well a bacterium can resist decolourisation by an alcohol/acid solution.
Acid fast organisms stain pink, non-acid-fast stain green
Mycobacterial characteristics 1) 2) 3) 4) 5) 6)
1) Acid fast rods
2) Non-motile
3) Aerobic
4) Unusual lipid-rich cell wall
5) Over 100 species in genus
6) Most are harmless saporophites
Mycobacterial opportunistic pathogens 1) 2) 3) 4) 5)
1) Marinum
2) Avium
3) Chelonae
4) Fortuitum
5) Abcessis
Are mycobacteria very fastidious?
No
Because of cell wall, can live in diverse environments
Atypical mycobacteria
Mycobacteria that don’t cause human disease
Mycobacterial cell wall
1) Peptidoglycan and arabinoglycan
2) Arabinoglycan is covalently linked to glycolipids and fatty acids (mycolic acid)
Ziehl-Neilson stain
An acid fast stain
Mycobacteria stain pink
Mycobacteria resistances and weaknesses
Resistant to detergent
HEat-labile (killed at over 60C)
What are the phylogenetic relationships in the Mycobacterium genus based on?
16S rRNA sequences
Broad division in Mycobacterium genus
Slow and fast growers
Do slow or fast growing Mycobacteria cause human disease?
Slow growing
Major human mycobacterial pathogens
1)
2)
3)
1) Tuberculosis
2) Leprae
3) Ulcerans
M tuberculosis generation time
24 horus
M leprae generation time
14 days
M ulcerans generation time
48 hours
Generation time
Time for bacteria to divide
M leprae treatment
Multi-drug treatment
Rifampcin, dapsone, clofazimine for at least 6 months
M tuberculosis treatment
Directly-observed treatment
Rifampcin, isoniazid and 1 other drug for ~ 6 months
M ulcerans treatment
Streptomycin, rifampcin for 8 weeks (SR8)
M leprae incidence
700,000
M tuberculosis incidence
8 million
M ulcerans incidence
100,000
Important part of the immune system in controlling mycobacterial infections
Th1, cellular immunity
M leprae cell tropism
Schwann cells, macrophages
M tuberculosis cell tropism
Mscrophages, monocytes
M ulcerans cell tropism
Subcutaneous tissue, maybe extracellular
M leprae pathology 1) 2) 3) 4) 5)
1) Leprosy
2) Neuritis
3) Paralysis
4) Mutilations
5) Erythema nodosum leprosum
Erythema nodosum leprosum
A subcutaneous granulomatous response that results in painful skin lesions
M tuberculosis pathology
10% disseminated TB
90% pulmonary TB
M ulcerans pathology
Buruli ulcer, necrosis
Proportion of global population infected with TB
1/3
Proportion of those infected with TB who will develop active infection
1/10
TB risk factors 1) 2) 3) 4) 5)
1) HIV coinfection
2) Alcoholism
3) Diabetes
4) Poverty
5) Anti-TNF treatments
How long until someone develops primary TB?
Several weeks - 2 years after infection
Hallmark primary lesion of TB
Ghon’s complex (calcified lesion in lungs)
What are primary and secondary TB?
Primary - Usually a Ghon complex, often presents in children. Normally is controlled, doesn’t come back.
Secondary - Reactivation of primary TB infection, much more damaging.
Secondary TB characteristics 1) 2) 3) 4) 5) 6) 7)
1) Often arises because of declining health
2) Extensive cell death and tissue destruction
3) Liquefaction of granuloma
4) Bacterial replication
5) Rupture into adjacent bronchi
6) Cavitation
7) Dissemination of bacilli
TB chromosome 1) 2) 3) 4)
1) 4.4Mb long
2) Single, circular chromosome
3) 4000 genes
4) G+C=~65%
Characteristics of TB genome
1)
2)
3)
1) Complex regulatory potential (13 sigma factors, over 100 transcriptional repressors and activators)
2) Varied metabolic and respiratory potential (can be aerobic, microaerophilic, anaerobic)
3) Abundance of genes involved in lipid metabolism (9% of genes)
How can TB pathogenic genes be found?
1)
2)
1) Gene KO
2) Comparing genome of TB to other, less pathogenic species (comparative genomics)
Virulence determinants found in TB through gene KO
1)
2) a, b, c
1) Genes in a 70kb chromosomal segment
2) Encode enzymes involved in cell wall lipid synthesis
a) Phthiocerol dimycocerosates (DIMs)
b) Phenolphthiocerol dimycocerosates (PDIMs)
c) Phenolic glycolipids (glycosylated PDIMs)
How might M TB cause disease?
Phenolic glycolipids and phenolphthiocerol dimycocerosates might block phagolysosome formation
M bovis and M tuberculosis 16S rRNA similarity
99.9% similarity
How was the BCG vaccine made?
M bovis strain attenuated by serial passage in media for 13 years
How is the BCG vaccine useful for finding TB virulence determinants?
Whole genome comparison between attenuated M bovis and virulent TB.
Differences between attenuated M bovis and virulent TB
1) Major genome deletions in BCG M bovis
2) RD1 is one such area
What is RD1?
1)
2)
3)
1) Encodes a novel secretion system in M tuberculosis (type VII secretion system, called Esx)
2) Secretes potent T cell antigens ESAT6 and CFP10
3) Required for escape from the phagolysosome
Part of TB genome that encodes a type VII secretion system
RD1
Encodes the Esx secretion system
Next step in comparative genome study after comparing BCG M bovis and TB
Compare the genomes of species in M tuberculosis complex
How are species in the M tuberculosis complex distinguished?
1) Presence or absence of InDels
2) Known as regions of difference
Effect of placing RD1 in M bovis
M bovis becomes more virulent
Differences between M leprae and TB genomes 1) 2) 3) 4) 5) 6) 7)
1) Leprae much smaller (3.3MB vs 4.4MB)
2) Leprae has smaller G+C percentage (57.8 vs 65.6)
3) ~1500 genes in common with TB
4) 1,114 pseudogenes
5) ~1,300 genes deleted
6) 100 Leprae specific genes
7) PGL locus is intact (PGL=phenolic glycolipid)
What are PGLs?
Phenolic glycolipids
Cell wall component, aid exit from the phagosome
Type of evolution that M leprae has undergone
Reductive evolution
What does PGL-1 bind to?
Native laminin-2 in the basal lamina of Schwann cell axons
Bacterium expressing PGL-1
M leprae
What might TB have evolved from?
An environmental mycobacterium - M marinum
M marinum 1) 2) 3) 4)
1) Thought to be the ancestor of TB
2) Infects fish
3) Disease state in fish resembles dermal tuberculosis
4) Level 2 organism, so relatively safe to handle in a lab
M marinum pathogenesis 1) 2) 3) 4) 5)
1) Survive and replicate in host macrophage phagosomes
2) Prevents lysosome fusion with Esx (T7SS)
3) Phagosomal escape
4) Actin-based motility
5) Cell-cell spread (T7SS role)
M marinum genome size vs TB
M marinum is 6.8MB and TB is 4.4MB
Similarity between TB and M marinum genomes
85% amino acid similarity
Some regions have been translocated, inverted
Results of comparing genomes of several mycobacterial species genomes with TB
1)
2)
3)
1) Always ~600 genes (600kb) that are unique to TB
2) These comprise 140 DNA regions of difference
3) M tuberculosis seems to have acquired at least 80 DNA regions of difference through lateral gene transfer
TB-specific genes
1)
a)
b)
1) Many encode known virulence factors
a) 20kb sulpholipid locus
b) Fumarate reductase locus
Putative TB evolution 1) 2) 3) a) b) c) d)
1) M marinum infected free-living amoebae
2) Acquired genes through lateral gene transfer, evolution
3) Gained:
a) Modified PGL locus
b) Modified respiratory potential
c) Sulpholipid locus
d) Modified Esx secretome
Fumarate reductase function
Allows TB to grow anaerobically
