Lecture 20 - E. Coli Flashcards
Ways to subtype E coli 1) 2) 3) 4) 5)
1) Serogroup/serotype
2) Multilocus sequence typing
3) Phage type
4) Pulsotype
5) Pathotype
What is the difference between serogroup and serotype?
Serogroup refers to O antigen
Serotype refers to H antigen
What gives the pulsotype?
RFLP of E coli genome
What is slowly replacing serotyping?
Multilocus sequence typing.
Multilocus sequence typing
1)
2)
1) Core genome clasification, not based on virulence factors
2) Sequence genes found in all E coli, compare them
Problem with serotyping
O, H antisera are required. These are expensive, produced in rabbits, so not completely accurate
What is phage typing used for?
Further defining serotypes of interest
What is pathotype based on?
Accessory genome
What can’t be pathotyped?
Opportunistic pathogens
Types of E coli causing intestinal infections
Primary pathogens
Types of E coli causing extra-intestinal infections
Opportunistic pathogens
Examples of extra-intestinal infections caused by E coli 1) 2) 3) 4) 5) 6)
1) Urinary tract infection
2) Neonatal meningitis
3) Septicaemia
4) Wound infection
5) Peritonitis
6) Pneumonia
Most common G- cause of septicaemia
E coli
Most common G+ cause of septiicaemia
Staph aureus
Pilus that aids E coli in infecting the bladder
Type 1 pili
What do type 1 pili help E coli with?
Bladder colonisation
Type of pili that help E coli colonise the kidneys
Pap pili
What do pap pili help E coli with?
Colonisation of the kidneys
Which virulence determinant helps E coli survive in the blood?
Capsule (K type)
Most important K type
K1
Identical to capsule of Neisseria meningitidis type B (sialic acid)
Proportion of E coli causing septicaemia and meningitis with K1
80%
Intestinal diseases caused by E coli 1) 2) 3) 4) 5) 6)
1) Non-specific infant diarrhoea
2) Traveller’s diarrhoea
3) Profuse watery diarrhoea
4) Dysentery
5) Haemorrhagic colitis
6) Diarrhoea-associated HUS
Haemolytic uremic syndrome symptoms
1)
2)
3)
1) Increased urea in blood
2) Erythrocyte lysis
3) Thrombocytopenia (low platelet count)
What is a neonate?
1st 28 days of life
MIcrobiological definition of an infant
Under 2 years of age
Some agents cause diarrhoea up until ~2 years
Subtypes of diarrhoeogenic E coli 1) 2) 3) 4) 5)
1) Enterotoxogenic E coli
2) Enteropathogenic E coli
3) Enterohaemorrhagic E coli
4) Enteroinvasive E coli
5) Enteroaggregative E coli
Another name for enteroinvasive E coli
Shigella
ETEC symptoms
Watery diarrhoea
EPEC symptoms
Non-specific diarrhoea in children
EHEC symptoms
Bloody diarrhoea, HUS
EIEC symptoms
Dysentery
EAEC symptoms
Watery diarrhoea
ETEC virulence factors
1)
2)
3)
1) Colonising factor antigen (CFA1)
2) Heat labile toxin
3) Heat stable toxin
Requirements for ETEC to cause illness
Needs both CFA and a toxin gene (either LT or ST or both)
Proportion of ETEC strains that only make ST
~1/3
Proportion of ETEC strain that make both ST and LT
~1/2
ETEC virulence factor in pigs
K88
Proven ETEC human colonisation factors
CFA/1, CFA/2, CFA/4
CFA/2 makeup
All have CS1 + either CS2 or CS3
CFA/4 makeup
All have CS4 + either CS5 or CS6
Putative ETEC human colonisation factors 1) 2) 3) 4) 5) 6)
1) CS7
2) CS8
3) CS12
4) CS14
5) CS17
6) PCFO148
What does CS3 attach to?
Microvili in the small intestine
Doesn’t cause damage or inflammation
Which part of shigatoxin is an enzyme?
A1 subunit
Heat labile toxin size
~86kD
Heat stable toxin size
~2kD
Heat labile toxin immunogenicity
High
Why is heat stable toxin immunogenicity low?
Because it is too small a peptide to elicit a lymphocyte response
Heat labile enterotoxin structure
AB5
Same structure as choleratoxin
A1 subunit is enzymatic
Why is heat stable enterotoxin so stable?
It has 3 disulphide links in the space of quite a short primary structure
Which hormone has the same mode of action as heat-stable enterotoxin?
Guanylin
What is guanylin?
Hormone
Same action as heat-stable enterotoxin
Why doesn’t guanylin cause pathology?
It only has two disulphide bonds, so it can be broken down by the body when not needed
What does heat labile enterotoxin act via?
Cyclic AMP
What does heat stable enterotoxin act via?
Cyclic GMP
Which enterotoxin acts via cyclic GMP?
Heat stable
Which enterotoxin acts via cyclic AMP
Heat labile
Effect of heat stable and heat labile enterotoxins on gut
Increase Cl- secretion from crypts
Decrease NaCl absorption by vili
Two-stage model of EPEC adherence
1)
2)
1) Plasmid-mediated. Bfp binds microvili
2) Chromosomal. Tir/intimin, attaching/effacing lesion
EPEC pathogenicity island
LEE
Locus for enterocyte effacement pathogenicity island
Locus for enterocyte effacement pathogenicity island contents
T3SS (EG: EspA)
Tir
Intimin
Effector proteins (EG: EspB, EspD)
EHEC virulence determinants 1) 2) 3) 4) 5) 6) 7)
1) Stx1
2) Stx2
3) Intimin
4) Efa
5) Secreted proteins (EspB)
6) Haemolysin
7) Serine protease (EspP)
What encodes Stx1 in EHEC?
Phage
What encodes Stx2 in EHEC?
Phage
Can Stx2 be neutralised by anti-Stx1?
No
Stx2 homology with Stx1
~60%
Shigatoxin processing 1) 2) 3) 4) 5)
1) Binds Gb3
2) Internalised into cell
3) In Golgi, broken into A and B subunits
4) In ER, broken into A1 and A2 subunits
5) A1 subunit binds 28S of 60S ribosomal subunit. Acts as a glycosidase.
Broader category of pathogenic E coli that EHEC fits into
STEC (shigatoxin-producing E coli)
Efa
EHEC factor for adhesion
Difference between STEC and EHEC
STEC is an E coli that produces shigatoxin
EHEC is an STEC with additional virulence determinants, that can cause haemolytic uremic syndrome or haemolytic colitis
Large E coli outbreak in Europe in 2011
E coli O104:H4
Enteroaggregative E coli
Death toll from 2011 enteroaggregative E coli outbreak
50
EHEC pathogenesis 1) 2) 3) 4) 5) 6)
1) Bacteria ingested in food or water (faecal contamination)
2) Attach to intestinal mucosa
3) Produce shigatoxin
4) Toxins absorbed
5) Damage to small blood vessels supplying gut, kidney, pancreas, heart, brain
6) HUS occurs when there is intravascular thrombosis and haemolysis
Why does shigatoxin damage small blood vessels? 1) 2) 3) 4) 5)
1) Shigatoxin is absorbed into the bloodstream through gut wall
2) Toxin damages endothelial cells, which leads to clotting cascade
3) This causes an intravascular thrombosis
4) Red blood cells are shorn on firbin in clot, leading to haemolysis
5) This interferes with blood supply to gut, other organs
How can kidneys be damaged by shigatoxin?
Kidney vasculature, nephrons have Gb3 receptors
How can EHEC infection cause diabetes?
Pancreas has Gb3 receptors in it.
Shigatoxin can lead to pancreatic damage
Is fragmented blood cells a symptom of many diseases?
No. Very uncommon.
Present in EHEC infections
Which shigatoxin is thought to be more toxic?
Stx2
