Diarrheagenic Escherichia Coli And Shigella

Front 1

Enterobacteriaceae bacteriology

Back 1

gram-negative facultative anaerobe
lives in the gut
ferments sugar (lactose positive)
motile

Front 2

E. coli structure

Back 2

Capsule, cell wall with peptidoglycan, pilus, chromosome, plasmids

Front 3

Basis of serotypes

Back 3

H antigen= flagella
O antigen= cell wall
K antigen= capsule

Front 4

Forms of horizontal gene transfer that generates E. coli pathotypes

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Transposons, pathogenicty islands, bacteriophages, plasmids, chromosomal mutations

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E. coli that cause HUS (hemolytic uremic syndrome) contain...

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Shiga toxin

Front 6

E. coli that cause dysentry have a plasmid containing...?

Back 6

Type 3 secretion system

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Good bacteria are:

Back 7

ubiquitous
harmless to each other
contribute to colonization resistance
produce beneficial metabolites

Front 8

Extraintestinal (ExPEC) E. coli strains (2)

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Uropathogenic (UPEC)
Strains associated with neonatal meningitis (MAEC)

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Diarrheagenic E. coli strains (8)

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Enterotoxigenic (ETEC)
Enteropathogenic (EPEC)
Enterohemorrhagic (EHEC)
Shiga-toxin producing (STEC)
Exteroaggregative (EAEC)
Enteroinvasive (EIEC)
Diffuse adhereing (DAEC)
Shigella

Front 10

E. coli diversity

Back 10

There is a set of genes common to all E. coli species and then a TON of variability in the remaining genome across strains

Front 11

ETEC pathogenesis:

Back 11

Spread by the fecal-oral route
Contains plasmid virulence factors such as: colonization factor antigens (adhesins that adhere to specific receptors), heat-labile enterotoxin, heat-stable enterotoxin

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ETEC is also known as....

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Traveler's diarrhea

Front 13

ETEC colonization factor antigens function and structure

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Bind to oligosaccharides on host tissues (mediate adherence to intestinal epithelium)
VARIED structures and antigenicity (the shape of the factors vary and adhesins are found on various parts of the factors)

Front 14

ETEC Heat-labile Enterotoxin injection

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Heat-labile enterotoxin is an AB toxin (A1= toxin)
A1 ADP ribosylates Gs which turns on adenylate cyclase constituitively. cAMP is then produced constituitively resulting in massive Cl- secretion out of the cell followed by intracellular fluid (watery diarrhea) and blocking of Na+ uptake into the cell

Front 15

ETEC Heat Stable Toxin Injection

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Guanylin= toxin receptor (responsible for regulating fluid balance in the gut)
3 disulfide bonds make it heat-stable
The toxin binds to guanylin which leads to the constituitive activation of guanylate cyclase. This results in the constituitive production of cGMP leading to Cl- efflux (along with intracellular water) and blocking Na+ uptake into the cell.

Front 16

Do ETEC Heat-toxin and Heat-labile toxin cause the same things to the host cell?

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YES- they both cause a massive efflux of Cl- followed by intracellular water and block Na+ reuptake.

Front 17

Besides action in the cell, what other similarities are there between ETEC heat-labile and heat-stable toxins?

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They are BOTH ADP-ribosylases

Front 18

Pathogenic effects of ETEC

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Watery diarrhea WITHOUT damage to the brush border; it is the MOST common cause of watery diarrhea in children and travelers in the developing world. This diarrhea is SELF-LIMITING.

Front 19

EPEC Basic Overview of Pathogenesis

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Localized adherence along the microvilli of the gut epithelial cells (plasmid-encoded pilus)
Attaches and causes the epithelial cells to slough off (via Type III secretion system on a pathogenicity island)
Causes severe diarrhea in infants of the developing world

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EPEC attaching and effacing lesions

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EPEC attaches to each other and to the host cell through its bundle forming pilus (BFP)
It uses a Type III secretion system to inject effector proteins into the cell
These effector proteins cause actin rearrangement within the cell leading to the formation of actin pedestals
The bacteria "surf" on top of these actin pedestals
The factors that allow it to attach and efface are encoded for on pathogenicity islands

Front 21

EPEC Bundle Forming Pilus

Back 21

This is encoded for on a plasmid
It allows bacteria to aggregate into microcolonies on top of host cells
It is REQUIRED for the bacteria's virulence
It is an adherence organelle

Front 22

EPEC Locus of Enterocyte Effacement

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This is a pathogenicty island that encodes factors required for attaching and effacing
It encodes the Type III secretion system, secreted proteins that cause actin rearrangement in the cell, Tir (its OWN receptor which it injects into the cell), and Intimin. Without this pathogenicity island the bacteria would not be virulent.

Front 23

Explain the Tir/Intimin relationship in EPEC

Back 23

Tir is EPEC's own receptor which it injects into the host cell using a Type III secretion system. EPEC also encodes for an Intimin protein that attaches to the Tir receptor on the host cell. This receptor and binding protein are what allow EPEC to bind to the host cell.

Front 24

What is the Type III secretion system and where did it come from (EPEC)?

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The type III secretion system can from another bacteria due to its DNA content and can be found in many bacterial species.
It developed from a flagellar assembly apparatus.
It is a complex apparatus that exports virulence factors in an energy-dependent manner from the bacteria and can inject these factors directly into the host cytoplasm.
It spans the double membrane and projects from the bacterial surface.
Its secretion is regulated and activated by host signals.
It is encoded for on a pathogenicity island.

Front 25

What type of bacteria have a Type III secretion system?

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It is ONLY found in Gram NEGATIVE bacteria.

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Does the Type III secretion system only confer 1 type of function in a single bacterial species?

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NO! Type III secretion systems are found in many different bacterial species and have many different functions within these species.

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EPEC Pathogenesis- Specific 3-stage model

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1) EPEC uses its bundle-forming toxin to bind to other bacteria and the host cell
2) The Type III secretion system is used to inject its own receptor (encoded by the Tir gene) and effector proteins that result in actin rearrangement within the host cell.
3) An actin pedestal is formed on which the bacteria can attach via Intimin binding to the receptor it injected into the host cell (Host protein 90) and it "surfs" on top of the host cell.

Front 28

Enterohemorrhagic E. Coli (EHEC) Reservoir and where you find it

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The reservoir of EHEC is cattle.
EHEC is found in contaminated food (ground beef, produce, juice), water (drinking and swimming), and petting zoos. It can also be transferred person to person.

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Is a lot or a little EHEC needed to cause disease and why?

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A LITTLE because of its acid resistance.

Front 30

What is the major EHEC culprit in the US? Does it ferment lactose or sorbitol?

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0157- it is the EHEC that evolved from EPEC

It ferments lactose
It DOES NOT ferment sorbitol

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EHEC 0157 Pathogenesis

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The 0157 EHEC bacteria have extra genes that allow it to stick to the walls of the intestine and produce the virulent Shiga toxin.

Front 32

What does Shiga toxin do?

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Shiga toxin injures the cells in the intestinal wall and blood vessels in the intestine. This leads to bleeding. It is a systemic toxin and once it gets into the blood stream it damages other blood vessels including those that go to the kidney resulting in renal failure. Shiga toxin inhibits protein synthesis.

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What type of diarrhea does EHEC cause? What else can EHEC cause?

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Bloody diarrhea (and non-blood diarrhea). EHEC can also cause Haemolytic uremic syndrome.

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How is EHEC similar to EPEC?

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EHEC is essentially the EPEC bacteria that also contains phage DNA that encodes the Shiga toxin. EHEC does everything EPEC does (pedestal formation, Type III secretion system, etc...)

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What are the main virulence factors of EHEC?

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EHEC contains the locus of enterocyte effacement (LEE found on EPEC) on its chromosome which encodes for the Type III secretion system, its own receptor it injects into the cell, effector proteins that cause actin rearrangement within the host cell, and a protein to bind to its receptor.
EHEC also has the phage DNA encoding for the Shiga-like toxin within its chromosome.
EHEC contains a plasmid that encodes for hemolysin which can damage epithelial cells.

Front 36

Binding and pathogenesis of EHEC

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EHEC binds to the host cell through its bundle-forming protein. It uses its Type III secretion system to inject effector proteins into the cell to cause actin rearragement and to inject its own receptor (Host Protein 90). It binds to Host Protein 90 via a protein on its surface, Intimin on the top of actin pedestals. It injects a Shiga-like toxin (AB toxin) that cleaves an adenosine in the 23S rRNA destroying the bacterial ribosome.
You get no protein synthesis and resulting cell death and tissue damage.

Front 37

What is the result of giving antibiotics to someone with EHEC?

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Antibiotics induce prophage induction and increase Shiga-like toxin production in EHEC bacteria. The antibiotics induce new prophages to form containing the DNA encoding for the Shiga-like toxin. These prophages lyse the bacteria and go on to infect more bacteria resulting in increased Shiga-like toxin production.

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Are there any vaccines against EHEC?

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Yes, for cows. Type III secreted proteins have been used in a vaccine to reduce the amount of 0157 EHEC found in the feces of cows. These vaccines are effective!

Front 39

What does EAEC cause?

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Childhood diarrhea in developing countries. This can cause a persistent disease and can be associated with growth retardation.
It is a significant cause of diarrhea among infants in the US.
This also causes travelers dirrhea.
HIV infected patients are more susceptible to EAEC

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Where is EAEC seen most frequently?

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Developing countries

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What does EAEC stand for?

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Enteroaggregative E. coli

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EAEC pathogenesis

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It contains aggregative adherence factors which are plasmid-encoded fimbriae
It causes damage to intestinal cells
It secretes 2 toxins: Pet and EAST

Front 43

What is one of the main ways EAEC causes destruction and of what?

Back 43

EAEC forms thick, mucus biofilms on intestinal mucosa mediated by its aggreagative adherence factors (fimbriae). The flagellin protein within its flagella triggers an inflamatory response by binding to TLR5 on the host cells. Some strains can produce toxins such as Pet and EAST. These EAEC bacteria cause distention of the enterocytes of the intestinal mucosa.

Front 44

What transcriptional activator governs the production of aggregative adherence factors in EAEC?

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AggR

Front 45

What is one effect of EAEC in young children?

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Acute gastroenteritis

Front 46

What strain of E. coli, as a result of horizontal gene transfer, can now cause Hemolytic-Uremic syndrome and what did it acquire that allowed it to do this?

Back 46

EAEC gained the Shiga-like toxin phage DNA allowing it to cause HUS in patients. This bacteria lacked the type 3 secretion system, did not adhere and efface, but the shiga toxin was enough to let it cause HUS.

Front 47

What is EIEC?

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Enteroinvasive E. Coli

Front 48

What other bacteria is EIEC most like?

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Shigella

Front 49

Explain the motility of EIEC

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EIEC spreads intracellularly through intestinal epithelium. it is able to enter a cell through a vacuole, lyse out of the vacuole and into the cytoplasm, replicate inside the cytoplasm, recruit actin to form a tail, and blast into adjacent cells without leaving the cell.

Front 50

What type of diarrhea does EIEC cause?

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Watery diarrhea

Front 51

What does Shiga-like toxin most commonly result in clinically?

Back 51

Kidney disease or damage

Front 52

What type of DNA is the invasion material of EIEC encoded on?

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EIEC has virulence regulators encoded on its chromosome and a Type III secretion system encoded on a plasmid.

Front 53

Can a clinical lab differentiate between all the different bacteria that cause diarrhea?

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YES

Front 54

What are the symptoms of ETEC and who/where does it infect?

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Watery diarrhea
It infects adults and children worldwide

Front 55

What are the symptoms of EPEC and who/where does it infect?

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Watery diarrhea
Infants esp. in developing countries

Front 56

What are the symptoms of EAEC and who/where does it infect?

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Watery, persistent diarrhea
Infants and AIDS patients

Front 57

What are the symptoms of EIEC and who/where does it infect?

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Bloody diarrhea
RARE; foodborne pathogen

Front 58

What are the symptoms of EHEC and who/where does it infect?

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Bloody diarrhea, hemorrhagic colitis, HUS, thrombit thrombocytopenic purpura
Sporadically seen in Western nations

Front 59

What is one way serotyping can identify differnet bacteria?

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Serotyping allows you to identify species based on the O (LPS), H (flagellar) and K (capsule) antigens they contain

Front 60

On what types of DNA have the virulence factors for E. coli been found?

Back 60

Plasmids, pathogenicity islands and bacteriophages

Front 61

If you have a patient with EHEC, what is causing their severe disease and how do you treat it?

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EHEC causes a severe illness due to the Shiga toxin. DO NOT give the patient antibiotics (due to induction of more toxin production from inducing phage formation)

Front 62

What type of bacteria is Shigella?

Back 62

Gram negative bacillus that are Enterobacteriaceae

Front 63

What effects does Shigella have on the host?

Back 63

Shigella invades the colonic epithelium. It causes dysentry (blood diarrhea) due to inflammation and damage. These effects are local (NOT systemic) and self-limiting.

Front 64

Is Shigella a lactose fermentor?

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NO

Front 65

Out of the O, H and K antigens, which one does Shigella lack?

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Shigella lacks flagella (the H antigen)

Front 66

What bacteria is Shigella closely related to/ basically the same species?

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E. Coli

Front 67

What are the 4 main types of Shigella bacteria?

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S. sonnei, S. flexneri, S. dysenteriae, S. boydii

Front 68

Where is S. sonnei most common and what type of symptoms does it cause?

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S. Sonnei is the most common in the US. It causes travelers diarrhea.

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Where is S. flexneri most common and what type of symptoms does it cause?

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S. flexneri is found worldwide. It causes travelers diarrhea.

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How severe is S. dysenteriae and what type of symptoms does it cause?

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S. dysenteriae is the most severe form of Shigella bacteria. It causes expolosive outbreaks and epidemics.

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How common is S. boydii?

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S. boydii is the least common form of Shigella.

Front 72

Are all Shigella human pathogens?

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YES

Front 73

What is dysentry?

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Blood diarrhea containing mucus and pus. It is indicative of a lot of tissue damage including damage of epithelial cells of the intestinal mucosa.

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What part of the world does Shigella cause most diarrhea and dysentery?

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The developing world

Front 75

What does Shigella do to children and infants?

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It causes persistent diarrhea, protein loss and malnutrition.

Front 76

Why is hygienic control of Shigella hard?

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This bacteria is acid-resistant and thus a small amount of the bacteria can cause disease since it can survive stomach acid. This bacteria has a low-infective dose.

Front 77

What are the reservoirs for Shigella?

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HUMANS; there are NO animal reservoirs

Front 78

How is Shigella transmitted?

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Person to person, foodborne outbreaks, water contamination. It is transmitted via fecal-oral contamination.

Front 79

What time of year is Shigella most common?

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During the summer with a rise in temperature

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Are cases of Shigella in the US increasing or decreasing?

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Decreasing (chlorinated water has helped to decrease its prevelance)

Front 81

How does Shigella enter the intestinal epithelial cells?

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Shigella binds to M (microfold) cells in our intestine. They pass through these cells and come out inside of the intestinal wall. There they are engulfed by macrophages. Shigella lyses the macrophages (mediates paratosis which results in the release of inflammatory cytokines such as IL1 and IL8) and enter the epithelial cells of the intestine through the basolateral side. Once inside the epithelial cells they can pass from cell to cell via actin filaments propulsion, without leaving the cells.

Front 82

What does Shigella infection do to the brush border of the intestinal epithelium?

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Shigella causes PMN infiltration and thus damage as well as causing complete brush border disorganization. The intestinal epithelium loses its integrity.

Front 83

What role does the Type III secretion system play in Shigella?

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The Type III secretion system targets the actin cytoskeletal by secreting effector proteins (invasion plasmin antigens (Ipa)) into the host cell cytoplasm. These proteins induce membrane ruffling and mediates epithelial cell invasion in which the epithelial cell is engulfed into a vacuole in the epithelial cell.

Front 84

What encodes for the Type III secretion system of Shigella and how is it activated?

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The Type III secretion system is encoded for on a virulence plasmid. It is activated by host cells and proteins. Similar structure are found in and responsible for the virulence of many different bacteria.

Front 85

What happens once Shigella is inside the epithelial cell?

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Once in the cell it can lyse from the vacuole and divide. These bacteria then polymerize actin tails and use them to propel themselves from cell to cell without leaving the inside of the host cells.

Front 86

How is the actin tail mediated in Shigella?

Back 86

Shigella utilizes actin via a VirG surface protein. Actin polymerization only occurs at the site closest to the bacterium and gives the energy needed to propel the bacteria forward. The actin Shigella utilizes is HOST actin. The actin DOES not move rather the tail is generated by constant depolymerization and polymerization. The IcsA protein on Shigella mediates actin polymerization.

Front 87

How is pro-inflammatory death induced in macrophages in response to a protein produced by Shigella?

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Shigella produces the protein IpaB (coming from the Type III secretion system). This protein binds to NOD receptors in the macrophage which leads to activation of a caspase protein leading to macrophage cell death.

Front 88

What term is used to describe macrophage cell death that occurs in response to Shigella?

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Paratosis- programmed cell death associated with inflammation.

Front 89

Does Shigella enter into the blood stream and become a systemic infection?

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NO, Shigella does NOT cause systemic disease

Front 90

What type of tissue does Shigella usually infect?

Back 90

Shigella infection occurs in the large intestine. It involves the intestinal lymphoid tissue.

Front 91

What are some ways Shigella causes damage?

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Shigella is both invasive and inflammatory. It induces pyroptosis of macrophages and the release of inflammatory mediators. It can cause a prolonged infection in which damage can persist after the infection is resolved.

Front 92

What are some special features of S. dysenteriae?

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This is the MOST virulent and infectious Shigella species. It secretes the Shiga toxin (bacteriophage encoded) which cleaves the 28S ribosomal rRNA.

Front 93

What are some diseases caused by S. dysenteriae?

Back 93

Severe colitis, neurological complications, and hemolytic uremic syndrome which can lead to anemia, thrombocytopenia and renal failure.

Front 94

What are some specific epidemiological features of S. dysenteriae?

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This bacteria affects ALL age groups, has high attack rates, high mortality and there are many multi-resistant strains. It is widespread throughout Central America, Asia and Africa.

Front 95

How should you treat S. dysenteriae?

Back 95

ANTIBIOTICS

Front 96

What type of DNA is found in ALL strains of Shigella?

Back 96

Virulence plasmid