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Bacteriology > Lecture 28 - Mycobacterial Infections > Flashcards

Lecture 28 - Mycobacterial Infections Flashcards

1
Q

Acid fast

A

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

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2
Q 
Mycobacterial characteristics
1)
2)
3)
4)
5)
6)
A

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

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3
Q 
Mycobacterial opportunistic pathogens
1)
2)
3)
4)
5)
A

1) Marinum
2) Avium
3) Chelonae
4) Fortuitum
5) Abcessis

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4
Q

Are mycobacteria very fastidious?

A

No

Because of cell wall, can live in diverse environments

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5
Q

Atypical mycobacteria

A

Mycobacteria that don’t cause human disease

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6
Q

Mycobacterial cell wall

A

1) Peptidoglycan and arabinoglycan

2) Arabinoglycan is covalently linked to glycolipids and fatty acids (mycolic acid)

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7
Q

Ziehl-Neilson stain

A

An acid fast stain

Mycobacteria stain pink

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8
Q

Mycobacteria resistances and weaknesses

A

Resistant to detergent

HEat-labile (killed at over 60C)

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9
Q

What are the phylogenetic relationships in the Mycobacterium genus based on?

A

16S rRNA sequences

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10
Q

Broad division in Mycobacterium genus

A

Slow and fast growers

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11
Q

Do slow or fast growing Mycobacteria cause human disease?

A

Slow growing

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12
Q

Major human mycobacterial pathogens
1)
2)
3)

A

1) Tuberculosis
2) Leprae
3) Ulcerans

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13
Q

M tuberculosis generation time

A

24 horus

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14
Q

M leprae generation time

A

14 days

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15
Q

M ulcerans generation time

A

48 hours

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16
Q

Generation time

A

Time for bacteria to divide

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17
Q

M leprae treatment

A

Multi-drug treatment

Rifampcin, dapsone, clofazimine for at least 6 months

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18
Q

M tuberculosis treatment

A

Directly-observed treatment

Rifampcin, isoniazid and 1 other drug for ~ 6 months

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19
Q

M ulcerans treatment

A

Streptomycin, rifampcin for 8 weeks (SR8)

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20
Q

M leprae incidence

A

700,000

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21
Q

M tuberculosis incidence

A

8 million

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22
Q

M ulcerans incidence

A

100,000

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23
Q

Important part of the immune system in controlling mycobacterial infections

A

Th1, cellular immunity

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24
Q

M leprae cell tropism

A

Schwann cells, macrophages

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25
Q

M tuberculosis cell tropism

A

Mscrophages, monocytes

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26
Q

M ulcerans cell tropism

A

Subcutaneous tissue, maybe extracellular

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27
Q 
M leprae pathology
1)
2)
3)
4)
5)
A

1) Leprosy
2) Neuritis
3) Paralysis
4) Mutilations
5) Erythema nodosum leprosum

28
Q

Erythema nodosum leprosum

A

A subcutaneous granulomatous response that results in painful skin lesions

29
Q

M tuberculosis pathology

A

10% disseminated TB

90% pulmonary TB

30
Q

M ulcerans pathology

A

Buruli ulcer, necrosis

31
Q

Proportion of global population infected with TB

A

1/3

32
Q

Proportion of those infected with TB who will develop active infection

A

1/10

33
Q 
TB risk factors
1)
2)
3)
4)
5)
A

1) HIV coinfection
2) Alcoholism
3) Diabetes
4) Poverty
5) Anti-TNF treatments

34
Q

How long until someone develops primary TB?

A

Several weeks - 2 years after infection

35
Q

Hallmark primary lesion of TB

A

Ghon’s complex (calcified lesion in lungs)

36
Q

What are primary and secondary TB?

A

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.

37
Q 
Secondary TB characteristics
1)
2)
3)
4)
5)
6)
7)
A

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

38
Q 
TB chromosome
1)
2)
3)
4)
A

1) 4.4Mb long
2) Single, circular chromosome
3) 4000 genes
4) G+C=~65%

39
Q

Characteristics of TB genome
1)
2)
3)

A

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)

40
Q

How can TB pathogenic genes be found?
1)
2)

A

1) Gene KO

2) Comparing genome of TB to other, less pathogenic species (comparative genomics)

41
Q

Virulence determinants found in TB through gene KO
1)
2) a, b, c

A

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)

42
Q

How might M TB cause disease?

A

Phenolic glycolipids and phenolphthiocerol dimycocerosates might block phagolysosome formation

43
Q

M bovis and M tuberculosis 16S rRNA similarity

A

99.9% similarity

44
Q

How was the BCG vaccine made?

A

M bovis strain attenuated by serial passage in media for 13 years

45
Q

How is the BCG vaccine useful for finding TB virulence determinants?

A

Whole genome comparison between attenuated M bovis and virulent TB.

46
Q

Differences between attenuated M bovis and virulent TB

A

1) Major genome deletions in BCG M bovis

2) RD1 is one such area

47
Q

What is RD1?
1)
2)
3)

A

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

48
Q

Part of TB genome that encodes a type VII secretion system

A

RD1

Encodes the Esx secretion system

49
Q

Next step in comparative genome study after comparing BCG M bovis and TB

A

Compare the genomes of species in M tuberculosis complex

50
Q

How are species in the M tuberculosis complex distinguished?

A

1) Presence or absence of InDels

2) Known as regions of difference

51
Q

Effect of placing RD1 in M bovis

A

M bovis becomes more virulent

52
Q 
Differences between M leprae and TB genomes
1)
2)
3)
4)
5)
6)
7)
A

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)

53
Q

What are PGLs?

A

Phenolic glycolipids

Cell wall component, aid exit from the phagosome

54
Q

Type of evolution that M leprae has undergone

A

Reductive evolution

55
Q

What does PGL-1 bind to?

A

Native laminin-2 in the basal lamina of Schwann cell axons

56
Q

Bacterium expressing PGL-1

A

M leprae

57
Q

What might TB have evolved from?

A

An environmental mycobacterium - M marinum

58
Q 
M marinum
1)
2)
3)
4)
A

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

59
Q 
M marinum pathogenesis
1)
2)
3)
4)
5)
A

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)

60
Q

M marinum genome size vs TB

A

M marinum is 6.8MB and TB is 4.4MB

61
Q

Similarity between TB and M marinum genomes

A

85% amino acid similarity

Some regions have been translocated, inverted

62
Q

Results of comparing genomes of several mycobacterial species genomes with TB
1)
2)
3)

A

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

63
Q

TB-specific genes
1)
a)
b)

A

1) Many encode known virulence factors
a) 20kb sulpholipid locus
b) Fumarate reductase locus

64
Q 
Putative TB evolution
1)
2)
3)
a)
b)
c)
d)
A

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

65
Q

Fumarate reductase function

A

Allows TB to grow anaerobically

Bacteriology (29 decks)

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