Lecture 20 - E. Coli Flashcards by Jack Cuthbertson

Ways to subtype E coli
1)
2)
3)
4)
5)

1) Serogroup/serotype
2) Multilocus sequence typing
3) Phage type
4) Pulsotype
5) Pathotype

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What is the difference between serogroup and serotype?

Serogroup refers to O antigen

Serotype refers to H antigen

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What gives the pulsotype?

RFLP of E coli genome

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What is slowly replacing serotyping?

Multilocus sequence typing.

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Multilocus sequence typing
1)
2)

1) Core genome clasification, not based on virulence factors

2) Sequence genes found in all E coli, compare them

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Problem with serotyping

O, H antisera are required. These are expensive, produced in rabbits, so not completely accurate

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What is phage typing used for?

Further defining serotypes of interest

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What is pathotype based on?

Accessory genome

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What can’t be pathotyped?

Opportunistic pathogens

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Types of E coli causing intestinal infections

Primary pathogens

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Types of E coli causing extra-intestinal infections

Opportunistic pathogens

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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

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Most common G- cause of septicaemia

E coli

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Most common G+ cause of septiicaemia

Staph aureus

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Pilus that aids E coli in infecting the bladder

Type 1 pili

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What do type 1 pili help E coli with?

Bladder colonisation

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Type of pili that help E coli colonise the kidneys

Pap pili

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What do pap pili help E coli with?

Colonisation of the kidneys

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Which virulence determinant helps E coli survive in the blood?

Capsule (K type)

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Most important K type

Identical to capsule of Neisseria meningitidis type B (sialic acid)

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Proportion of E coli causing septicaemia and meningitis with K1

80%

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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

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Haemolytic uremic syndrome symptoms
1)
2)
3)

1) Increased urea in blood
2) Erythrocyte lysis
3) Thrombocytopenia (low platelet count)

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What is a neonate?

1st 28 days of life

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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?

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

``` 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