Pathogenic E.coli Flashcards
(133 cards)
1
Q
E.coli family?
A
Enterobacteriaceae
2
Q
E.coli genus?
A
Escherichia
3
Q
What type of anaerobe is E.coli?
A
Facultative anaerobe
4
Q
How many bacteria colonise humans?
A
10^13 - 10^14
5
Q
Bacteria contribute how much to our body weight?
A
2kg
6
Q
Two most dominant commensal phyla?
A
Bacteriodetes and firmicutes
7
Q
Benefits of gut commensals?
A
- Provide essential and non-essential amino acids
- Direct and indirect colonisation resistance
- Provide short chain fatty acids (SCFAs) such as butyrate which are used by the intestinal epithelial cells as a main fuel/energy source
- Provide vitamins such as vitamin B12, Vitamin K, Riboflavin and Biotin
8
Q
Non-pathogenic E.coli are the predominant?
A
Facultative anaerobe in the gut
9
Q
Pathogenic E.coli that causes UTIs?
A
UPEC
Uropathogenic E.coli
10
Q
Pathogenic E.coli that causes neonatal meningitis?
A
NMEC
Neonatal meningitis E.coli
11
Q
Name all the pathogenic E.coli able to cause enteric/diarrhoeal disease?
A
EAEC- Enteroaggregative E.coli ETEC- Enterotoxigenic E.coli EIEC- Enteroinvasive E.coli EHEC- Enterohaemorrhagic E.coli EPEC- Enteropathogenic E.coli
12
Q
Which pathogenic E.coli is the main cause of traveller’s diarrhoea?
A
ETEC- Enterotoxigenic E.coli
13
Q
Which pathogenic E.coli is the second most common cause of traveller’s E.coli?
A
EAEC- Enteroaggregative E.coli
14
Q
How can pathogenic E.coli be categorised/serotyped?
A
Based on the O and H antigens
15
Q
O antigen?
A
LPS antigen
Consists of many repeats of an oligosaccharide unit
16
Q
H antigen?
A
Flagellar antigen
17
Q
Describe the structure of the LPS?
A
Has a lipid A base
This is attached to a core region
The core is then attached to the O antigen
18
Q
What is the O antigen?
A
Consists of many repeats of an oligosaccharide unit
Part of the LPS
19
Q
What is LPS?
A
It is an endotoxin
It is lipopolysaccharide
20
Q
How did pathogenic E.coli form?
A
Thought to have evolved from commensal E.coli
Through the loss and gain of genes
21
Q
How many genes are conserved between pathogenic and commensal E.coli and what are these genes called?
A
~3000 genes
These genes are house-keeping genes and are conserved as they are essential
22
Q
How can pathogenic E.coli be serotyped?
A
Based on the O and H antigens
23
Q
What does pathogenic E.coli require to cause disease?
A
- Access to the host
- Must be able to colonise a surface in the host
- Must be adapted to the environment it colonises
- Must be able to obtain nutrients
- Must be able to reproduce
- Must be able to evade the host immune defences
24
Q
Which enteric/diarrhoeal E.coli are extracellular?
A
EAEC
EHEC
EPEC
ETEC
25
Which of the enteric/diarrhoeal E.coli are intracellular invasive pathogens?
EIEC
26
How does the immune system recognise the bacteria, describe the TLRs?
TLR5 recognises flagellin
TLR4 recognises LPS of gram negative bacteria
TLR2 recognises gram positive bacteria
27
TLRs 5,2,4 signal via
Myd88 which induces NF-kB
28
UPEC is the most common cause of?
Nosocomial and community acquired UTIs
29
UPEC colonisation factors?
Type I pili
P pili
S pili
30
Type I pili are used by UPEC to colonise?
The bladder
31
Type P pili are used by UPEC to colonise?
The kidney
32
What toxins/virulence determinants are produced by UPEC?
HlyA
CNF1
Sat toxin
33
What does UPEC HlyA do?
It is an alpha haemolysin
It is a pore forming toxin
Can form pores in e.g. neutrophils to induce cell death
34
What does UPEC CNF1 do?
It an inhibit phagocytosis
35
What does UPEC Sat toxin do?
Can lead to urothelial cell exfoliation
36
What is UPEC Sat toxin?
It is a SPATE
| Serine Protease Autotransporter of Enterobacteriaceae
37
What are SPATEs?
Serine Protease Autotransporters of Enterobacteriaceae
38
What are some siderophores of UPEC?
IroN
IreA
Aerobactin
39
What do siderophores bind to?
Ferric (Fe3+) iron
40
EIEC has the same method of infection as?
Shigella
41
Which pathogenic E.coli are T3SS dependent?
EHEC
EPEC
EIEC
42
Which pathogenic E.coli are T3SS independent?
ETEC
| EAEC
43
EAEC is the second most common cause of?
Traveller's diarrhoea
44
EAEC colonises where?
Ileum of the small intestine
| Large intestine/colon
45
Symptoms of EAEC infection?
Watery diarrhoea with or without the presence of mucus/blood
46
Treatment of EAEC?
Rehydration therapy
Self limiting- should get better without treatment
Although antibiotics can be given to speed up recovery
47
Why is EAEC known as aggregative E.coli?
Due to the characteristic aggregative adherence structure it forms
48
Three stages of EAEC pathogenesis?
1) Colonisation via AAF (aggregative adherence fimbriae)
2) Biofilm formation
3) Release of toxins and elicitation of an inflammatory response, mucosal toxicity, and intestinal secretion
49
What is the colonisation factor of EAEC?
AAF which is aggregative adherence fimbriae
50
How do the aggregates form?
Through the bacteria binding to the epithelial cell surface and through binding to each other
51
What promotes expression of AAF?
AggR transcription regulator
52
Enteroaggregative Escherichia coli (EAEC) adherence to human intestinal tissue is mediated by?
AAF = aggregative adherence fimbriae
53
What are key virulence determinants of EAEC?
SPATEs= Pic and Pet
EAST-1
ShET1
54
What are SPATEs?
Serine protease autotransporters of Enterobacteriaceae
55
What are the SPATEs important in EAEC virulence?
Pet and Pic
56
How are Pet and Pic secreted?
Via the T5SS: Type V secretion system
57
What is Pet?
Plasmid encoded toxin
58
What does Pet do?
Interferes with cytoskeleton integrity and results in cell death
59
What does Pic do?
Involved in intestinal colonisation
It is a mucinase
Allows penetration through the mucus layer
60
What is Pic?
It is a mucinase
| Allows contact with the epithelium by allowing penetration through the mucus layer
61
How does EAEC cause watery diarrhoea?
EAST1
| ShET1
62
What does EAST1 do?
This toxin causes increased secretion of chloride and has been associated with secretory diarrhoea
63
When was the EAEC outbreak in Germany?
2011
64
How many people died in the EAEC outbreak in Germany?
~50
65
What was the serotype of the EAEC that caused the outbreak in Germany?
O104:H4
66
Why was O104:H4 EAEC so deadly?
It was an enteroaggregative E.coli that was able to produce Shiga toxin. This made it an excellent and very virulent coloniser.
67
ETEC colonises which part of the body?
The small intestine
68
ETEC is the main cause of?
Traveller's diarrhoea
69
ETEC is the leading cause of death in?
Children <5 years of age
70
How does ETEC colonise?
EtpA
71
What is EtpA?
It is an adhesin
Interacts with the tips of ETEC flagella to promote adhesion by forming molecular bridges between the bacteria and the epithelial surface
72
What toxins does ETEC secrete?
ST and LT toxins
73
ST toxin?
Heat Stable Toxin
74
LT toxins?
Heat Labile Toxin
75
Which is larger ST or LT?
Lt is larger than ST
76
Which toxin is very similar to the cholera toxin?
LT
| Heat Labile toxin
77
Structure of the heat labile LT toxin?
A subunit and 5 identical B subunits
78
What receptor does LT bind to?
GM1 receptor- same receptor that the cholera toxin binds to
79
What is GM1?
Ganglioside receptor
80
What does the B subunit of LT do?
Binds to the GM1 ganglioside receptor
81
What does the A subunit of LT do?
Has the biological enzymatic activity
82
LT remains associated with outer membrane vesicles via?
Interactions with LPS
83
What is a proposed reason for ETEC being a milder disease than cholera?
Lots of cholera toxin can be secreted. However, ETEC LT is associated with outer membrane vesicles due to interactions with LPS, so smaller amounts reach host cells
84
How does LT cause disease?
Associated with outer membrane vesicles
Comes into contact with GM1 ganglioside receptor
B subunit binds GM1 and the vesicle is endocytosed
A subunit can lead to cAMP activation
CFTR is phosphorylated and activated
Cl- ions move into the lumen of the intestines. Followed by Na+ and water.
High levels of water cause watery diarrhoea
85
How does ST cause disease?
Binds to guanylyl cyclase C (GC-C) on the intestinal epithelium
Activates the intracellular domain of guanylyl cylase
Leads to intracellular accumulation of cGMP
Activates cGMP-dependent protein kinase II
Phosphorylation of CFTR
Cl- secretion
86
ST binds and activates?
Guanylyl cylase C (GC-C)
87
LT binds?
GM1 ganglioside
88
What are the T3SS dependent pathogenic E.coli?
EIEC
EHEC
EPEC
89
What are the main differences between EHEC and EPEC?
EHEC has a natural reservoir in cattle
| EHEC can produce Shiga toxin
90
As EHEC produces shiga toxin it can be known as?
STEC
| Shiga toxin producing E.coli
91
EPEC colonises?
The small intestine
92
EHEC colonises?
The large intestine
93
What is the main symptom of EHEC infection?
Bloody diarrhoea
94
Which serotype of EHEC causes lots of infections due to infected lettuce and food?
O157:H7
95
The T3SS of EPEC and EHEC is encoded by?
LEE
| Locus of enterocyte effacement
96
What does LEE stand for?
Locus of enterocyte effacement
97
What is LEE, the locus of enterocyte effacement?
It is a 35.6 kb pathogenicity island
98
What does LEE encode?
Encodes the T3SS as well as effectors such as adhesin intimin and Tir
99
How was the LEE pathogenicity island obtained?
Through horizontal gene transfer
100
What can the T3SS be described as?
A molecular syringe
101
Describe the T3SS structure?
Have rings which provide a continuous path between the inner and outer membranes. Attached to the outer-membrane ring is a needle. The needle capped and extended by a filamentous extension (EspA). EspB and EspD assemble at the tip of EspA and insert into the host membrane to form a pore.
102
What extends the needle of the T3SS in EPEC and EHEC?
EspA filamentous extension
103
What is found at the tip of the EspA filamentous extension?
EspB and EspD
104
What does the EspA filamentous extension allow?
EspA is thought to facilitate attachment to the host cells through the thick glycocalyx layer
105
Shigella T3SS lacks?
EspA filamentous extension
106
As Shigella T3SS lacks EspA it cannot?
Shigella lacks the additional extension which means it cannot facilitate attachment to host cell through the thick glycocalyx layer.
107
What are some T3SS effectors in EHEC/EPEC?
```
Tir
Adhesin intimin
EspH
EspM
EspT
Nlec
```
108
Tir and intimin allow for?
Intimate adherence
109
What forms as a result of EPEC/EHEC intimate adherence?
A/E lesions
110
How is intimate adherence established?
Tir enters host cells via T3SS and embeds into the host cell membrane- hairpin loop extends extracellularly
Intimin is expressed on the bacterial cell surface and binds Tir
111
What happens once Tir and intimin bind?
Formation of actin rich pedestals
| N-WASP is activated and can tripper Arp2/3 actin polymerisation
112
What are A/E lesions?
Formed as a result of intimate adhesion
Characterised by intimate binding, destruction of the brush border microvilli and accumulation of polymerised actin to form a pedestal structure.
113
When are Rho GTPases active?
When bound to GTP
114
When are Rho GTPases inactive?
When bound to GDP
115
What are Rho GTPases?
Family of G proteins
116
Rho GTPases have a function in?
Regulating intracellular actin dynamics
117
How are Rho GTPases activated/ when can signalling occur?
When Rho GTPases are bound to GTP
| Can be activated by GEFs which exchange GDP for GTP allowing signalling to occur
118
How are Rho GTPases inactivated/how can signalling be terminated?
Can stimulate the GTPase activity of Rho GTPases causing GTP-->GDP. This terminates signalling.
119
How can EspH impact Rho GTPase signalling?
Directly prevents GEFs binding to Rho and prevents Rho activation.
120
How can EspM and EspT impact Rho GTPase signalling?
Can activate Rho through molecular mimicry
121
What is the overall purpose of EspH, EspM and EspT?
Shuts down the host's ability to control signalling through Rho and has it's own way of controlling Rho GTPase signalling
122
What does NleC do?
It is a protease and is able to cleave the p65 subunit of NF-kB to inhibit TLR signalling
123
Shiga toxin structure?
5 B subunits
| 1 A subunit
124
B subunit of shiga toxin binds?
Gb3
125
A subunit of shiga toxin does what?
Can cleave the 28S rRNA of the 60S ribosome which disrupts protein synthesis and induces apoptosis
126
Why are cattle not impacted by shiga toxin?
Endothelial cells of cattle do not express Gb3 which prevents shiga toxin binding blood vessels in the gastrointestinal tract of cattle.
127
Why should EHEC not be treated with antibiotics?
Shiga toxin is encoded by a phage. Shiga toxin is produced during the lytic stage of the phage cycle. Antibitoics can induce stress which causes the phage to enter the lytic cycle= even more shiga toxin produced.
128
Why should EHEC not be treated with antibiotics?
Shiga toxin is encoded by a phage. Shiga toxin is produced during the lytic stage of the phage cycle. Antibiotics can induce stress which causes the phage to enter the lytic cycle= even more shiga toxin produced.
129
ETEC infects the?
Small intestine
130
EAEC infects the?
Ileum of the small intestine/ large intestine
131
EHEC infects the?
Large intestine
132
Shigella infects the?
Large intestine
133
EPEC infects the?
Small intestine
