Pathogenic E.coli Flashcards
E.coli family?
Enterobacteriaceae
E.coli genus?
Escherichia
What type of anaerobe is E.coli?
Facultative anaerobe
How many bacteria colonise humans?
10^13 - 10^14
Bacteria contribute how much to our body weight?
2kg
Two most dominant commensal phyla?
Bacteriodetes and firmicutes
Benefits of gut commensals?
- 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
Non-pathogenic E.coli are the predominant?
Facultative anaerobe in the gut
Pathogenic E.coli that causes UTIs?
UPEC
Uropathogenic E.coli
Pathogenic E.coli that causes neonatal meningitis?
NMEC
Neonatal meningitis E.coli
Name all the pathogenic E.coli able to cause enteric/diarrhoeal disease?
EAEC- Enteroaggregative E.coli ETEC- Enterotoxigenic E.coli EIEC- Enteroinvasive E.coli EHEC- Enterohaemorrhagic E.coli EPEC- Enteropathogenic E.coli
Which pathogenic E.coli is the main cause of traveller’s diarrhoea?
ETEC- Enterotoxigenic E.coli
Which pathogenic E.coli is the second most common cause of traveller’s E.coli?
EAEC- Enteroaggregative E.coli
How can pathogenic E.coli be categorised/serotyped?
Based on the O and H antigens
O antigen?
LPS antigen
Consists of many repeats of an oligosaccharide unit
H antigen?
Flagellar antigen
Describe the structure of the LPS?
Has a lipid A base
This is attached to a core region
The core is then attached to the O antigen
What is the O antigen?
Consists of many repeats of an oligosaccharide unit
Part of the LPS
What is LPS?
It is an endotoxin
It is lipopolysaccharide
How did pathogenic E.coli form?
Thought to have evolved from commensal E.coli
Through the loss and gain of genes
How many genes are conserved between pathogenic and commensal E.coli and what are these genes called?
~3000 genes
These genes are house-keeping genes and are conserved as they are essential
How can pathogenic E.coli be serotyped?
Based on the O and H antigens
What does pathogenic E.coli require to cause disease?
- 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
Which enteric/diarrhoeal E.coli are extracellular?
EAEC
EHEC
EPEC
ETEC
Which of the enteric/diarrhoeal E.coli are intracellular invasive pathogens?
EIEC
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
TLRs 5,2,4 signal via
Myd88 which induces NF-kB
UPEC is the most common cause of?
Nosocomial and community acquired UTIs
UPEC colonisation factors?
Type I pili
P pili
S pili
Type I pili are used by UPEC to colonise?
The bladder
Type P pili are used by UPEC to colonise?
The kidney
What toxins/virulence determinants are produced by UPEC?
HlyA
CNF1
Sat toxin
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
What does UPEC CNF1 do?
It an inhibit phagocytosis
What does UPEC Sat toxin do?
Can lead to urothelial cell exfoliation
What is UPEC Sat toxin?
It is a SPATE
Serine Protease Autotransporter of Enterobacteriaceae
What are SPATEs?
Serine Protease Autotransporters of Enterobacteriaceae
What are some siderophores of UPEC?
IroN
IreA
Aerobactin
What do siderophores bind to?
Ferric (Fe3+) iron
EIEC has the same method of infection as?
Shigella
Which pathogenic E.coli are T3SS dependent?
EHEC
EPEC
EIEC
Which pathogenic E.coli are T3SS independent?
ETEC
EAEC
EAEC is the second most common cause of?
Traveller’s diarrhoea
EAEC colonises where?
Ileum of the small intestine
Large intestine/colon
Symptoms of EAEC infection?
Watery diarrhoea with or without the presence of mucus/blood
Treatment of EAEC?
Rehydration therapy
Self limiting- should get better without treatment
Although antibiotics can be given to speed up recovery
Why is EAEC known as aggregative E.coli?
Due to the characteristic aggregative adherence structure it forms
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
What is the colonisation factor of EAEC?
AAF which is aggregative adherence fimbriae
How do the aggregates form?
Through the bacteria binding to the epithelial cell surface and through binding to each other
What promotes expression of AAF?
AggR transcription regulator
EnteroaggregativeEscherichia coli(EAEC) adherence to human intestinal tissue is mediated by?
AAF = aggregative adherence fimbriae
What are key virulence determinants of EAEC?
SPATEs= Pic and Pet
EAST-1
ShET1
What are SPATEs?
Serine protease autotransporters of Enterobacteriaceae
What are the SPATEs important in EAEC virulence?
Pet and Pic
How are Pet and Pic secreted?
Via the T5SS: Type V secretion system
What is Pet?
Plasmid encoded toxin
What does Pet do?
Interferes with cytoskeleton integrity and results in cell death
What does Pic do?
Involved in intestinal colonisation
It is a mucinase
Allows penetration through the mucus layer
What is Pic?
It is a mucinase
Allows contact with the epithelium by allowing penetration through the mucus layer
How does EAEC cause watery diarrhoea?
EAST1
ShET1
What does EAST1 do?
This toxin causes increased secretion of chloride and has been associated with secretory diarrhoea
When was the EAEC outbreak in Germany?
2011
How many people died in the EAEC outbreak in Germany?
~50
What was the serotype of the EAEC that caused the outbreak in Germany?
O104:H4
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.
ETEC colonises which part of the body?
The small intestine
ETEC is the main cause of?
Traveller’s diarrhoea
ETEC is the leading cause of death in?
Children <5 years of age
How does ETEC colonise?
EtpA
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
What toxins does ETEC secrete?
ST and LT toxins
ST toxin?
Heat Stable Toxin
LT toxins?
Heat Labile Toxin
Which is larger ST or LT?
Lt is larger than ST
Which toxin is very similar to the cholera toxin?
LT
Heat Labile toxin
Structure of the heat labile LT toxin?
A subunit and 5 identical B subunits
What receptor does LT bind to?
GM1 receptor- same receptor that the cholera toxin binds to
What is GM1?
Ganglioside receptor
What does the B subunit of LT do?
Binds to the GM1 ganglioside receptor
What does the A subunit of LT do?
Has the biological enzymatic activity
LT remains associated with outer membrane vesicles via?
Interactions with LPS
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
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
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
ST binds and activates?
Guanylyl cylase C (GC-C)
LT binds?
GM1 ganglioside
What are the T3SS dependent pathogenic E.coli?
EIEC
EHEC
EPEC
What are the main differences between EHEC and EPEC?
EHEC has a natural reservoir in cattle
EHEC can produce Shiga toxin
As EHEC produces shiga toxin it can be known as?
STEC
Shiga toxin producing E.coli
EPEC colonises?
The small intestine
EHEC colonises?
The large intestine
What is the main symptom of EHEC infection?
Bloody diarrhoea
Which serotype of EHEC causes lots of infections due to infected lettuce and food?
O157:H7
The T3SS of EPEC and EHEC is encoded by?
LEE
Locus of enterocyte effacement
What does LEE stand for?
Locus of enterocyte effacement
What is LEE, the locus of enterocyte effacement?
It is a 35.6 kb pathogenicity island
What does LEE encode?
Encodes the T3SS as well as effectors such as adhesin intimin and Tir
How was the LEE pathogenicity island obtained?
Through horizontal gene transfer
What can the T3SS be described as?
A molecular syringe
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.
What extends the needle of the T3SS in EPEC and EHEC?
EspA filamentous extension
What is found at the tip of the EspA filamentous extension?
EspB and EspD
What does the EspA filamentous extension allow?
EspA is thought to facilitate attachment to the host cells through the thick glycocalyx layer
Shigella T3SS lacks?
EspA filamentous extension
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.
What are some T3SS effectors in EHEC/EPEC?
Tir Adhesin intimin EspH EspM EspT Nlec
Tir and intimin allow for?
Intimate adherence
What forms as a result of EPEC/EHEC intimate adherence?
A/E lesions
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
What happens once Tir and intimin bind?
Formation of actin rich pedestals
N-WASP is activated and can tripper Arp2/3 actin polymerisation
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.
When are Rho GTPases active?
When bound to GTP
When are Rho GTPases inactive?
When bound to GDP
What are Rho GTPases?
Family of G proteins
Rho GTPases have a function in?
Regulating intracellular actin dynamics
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
How are Rho GTPases inactivated/how can signalling be terminated?
Can stimulate the GTPase activity of Rho GTPases causing GTP–>GDP. This terminates signalling.
How can EspH impact Rho GTPase signalling?
Directly prevents GEFs binding to Rho and prevents Rho activation.
How can EspM and EspT impact Rho GTPase signalling?
Can activate Rho through molecular mimicry
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
What does NleC do?
It is a protease and is able to cleave the p65 subunit of NF-kB to inhibit TLR signalling
Shiga toxin structure?
5 B subunits
1 A subunit
B subunit of shiga toxin binds?
Gb3
A subunit of shiga toxin does what?
Can cleave the 28S rRNA of the 60S ribosome which disrupts protein synthesis and induces apoptosis
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.
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.
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.
ETEC infects the?
Small intestine
EAEC infects the?
Ileum of the small intestine/ large intestine
EHEC infects the?
Large intestine
Shigella infects the?
Large intestine
EPEC infects the?
Small intestine
