E. Coli

Question 1

E.coli- general characteristics

Answer 1

Many strands of E. coli are commensals of mammalian gut
Ferment lactose
indole positive (produce indole from tryptophan)
Most strains are flagellated
some strains have capsules–> cause extra-intestinal disease, usually hemolytic on blood agar
some strains have beta hemolysis on sheep blood agar
E. coli causing septicemia are hemolytic

Question 2

E. coli- diseases it can cause

Answer 2

Neonatal and post-weaning diarrhea- many species
Neonatal septicemia- many species
Mastitis- many species–> 25-30% of mastitis caused by e.coli
UTI- many species
Hemorrhagic colitis and hemolytic uremia syndrome in humans (E. coli O157)
Oedema disease- pigs
Watery mouth- lambs–> overwhelming e.coli septicemia
Infection of existing lesions- many species–> mixed infection in gut.

Question 3

E. coli pathogens

Answer 3

Enterotoxigenic E. coli–> ETEC- animals and humans
Enteropathogenic E. coli–> EPEC, AEEC- animals and humans
Verotoxigenic E. Coli–> VTEC/STEC- animals and humans (no symptoms in animals)
(Enterohemorrhagic E. Coli EHEC in man)
Enteroaggregative E. coli (EAEC), Diffusely adherent e. coli (DAEC), enteroinvasive E. coli (EIEC) all in humans

Extra-intestinal pathogenic e. coli ExPEC- animals and humans
-non-enteric infections- UTIs, mastitis, septicemia, meningitis

NB: generally strains that cause disease in animals don’t cause disease in humans (c.f. salmonella which as broad host range serotypes).
EXCEPTION: E. coli O157 is zoonotic, but animals are asymptomatic.

Question 4

Virulence factors of Enterotoxigenic E. coli (ETEC)

Answer 4

heat labile enterotoxin (LT), heat stable enterotoxin (ST), particular fimbriae (allow targeting of gut tissue)

Question 5

Virulence factors of Enteropathogenic E. coli

Answer 5

pathogenicity island (LEE), TTSS, intimin, particular fimbriae

Question 6

Virulence factors of Enterohemorrhagic E. coli (O157)

Answer 6

pathogenicity island (LEE), TTSS, intimin, fimbriae and also acquired toxins (verotoxins/shiga-like toxins).

Question 7

Virulence factors of Extra-intestinal pathogenic e. coli (ExPEC)

Answer 7

causes septicemia, UTIs–> hemolysin, iron-uptake systems, particular fimbriae and capsules–> genes required for an extra-intestinal life style
Mastitis has no particular virulence factors- perhaps it’s just an opportunist infection.

Question 8

ExPEC infections of animals

Answer 8

Cows and Pigs: mastitis and septicemia
Dogs and Cats: UTIs, pyometra and septicemia
Poultry: air sacculitis, septicemia, cellulitis, yolk sac infection

Question 9

Relation between commensal e. coli, septicemic pathogens and enteric pathogens

Answer 9

If you look at commensals of E. coli in gut, we see the same strains that cause septicemia and UTIs. ExPEC e. coli are carried in the gut, but don’t cause pathology there. intestinal pathologic e. coli must be acquired from another animal.

Question 10

ExPEC virulence factors

Answer 10

Capsule- K antigen- survival within tissue/blood
Fimbriae (Pili): particularly imp. in UTI–> adhere to kidney/organ to avoid being flushed away
Toxins:1) hemolysin- effect on RBCs and WBCs
2) Cytotoxic necrotizing factor 1

Siderophores for scavenging iron

1) Enterochelin (enterobactin) found in pathogenic and commensal E. coli- produced by all E. coli strains; genes found on chromosomes
2) aerobactin: not all E. coli strains produce; genes found on plasmid.

Question 11

Enterochelin vs. Aerobactin Siderophores

Answer 11

Enterochelin has a greater affinity for iron than aerobactin in vitro, but it’s suggested that pathogenic organisms ALL use aerobactin. Why? Enterobactin is bound by serum albumin, which inactivates it. Therefore, it can’t scavenge/return iron back to the bacterium. Anti-enterochelin ABs are produced. At a lower pH, aerobactin has a higher affinity for iron than enterochelin. No ABs are produced for aerobactin.

Question 12

Enterotoxigenic E. Coli (ETEC)

Answer 12

non-invasive: just sit on mucosal surface–> that’s their mechanism of disease
Non-inflammatory, watery diarrhea
non-zoonotic: human strains don’t infect animals and vice versa
acute diarrhea in young animals–> life threatening. die d/t dehydration.

Question 13

Mulitfactorial virulence of ETEC

Answer 13

one plasmid carries the toxin which causes diarrhea, and one plasmid carries the fimbriae which help colonize. To have disease occuring, must have both. Toxins result in not only water NOT getting absorbed, but also results in active secretion of water.

Question 14

E. coli fimbriae

Answer 14

E. coli fimbriae action is SPECIFIC. it recognized species-specific receptors
K88=F4--> pigs
K99=F5--> pigs, sheep, calbes
F6= pigs and calves
F41= pigs and calves
Human ETEC have different fimbriae.

Question 15

ETEC toxins- mechanisms of LT and ST

Answer 15

action of heat labile (LT) and heat stable toxins (ST)
LT binds to receptor and modulates expression of G-protein. Transfers ADP ribose–> turns on/up-regulates adenylate cyclase–> increases cAMP-> activates protein kinase A–> opens channels for fluid secretion.
ST binds to receptor to up-regulate guanylate cyclase–> increase cGMP which prevents water absorption.
Can have one, or the other, or both toxins produced by a strain of E. coli

Question 16

LT toxin

Answer 16

highly immunogenic. 1A subunit with enzyme ADP-ribosyltransferase and 3 B subunits which bind receptors
V. similar to cholera toxin

Question 17

ST toxin

Answer 17

non-immunogenic d/t small size. small, single peptide
2 types: 1) STa produced by human and animals strains 2) STb produced by porcine e. coli strains
Genes for both types of toxins are carried on plasmids.

Question 18

Diarrhea: ETEC vs. Salmonella species

Answer 18

E. coli: remain extra-cellular–> non-inflammatory diarrhea

Salmonella: invade cells- intracellular location –> inflammatory diarrhea.

Question 19

Enteropathogenic E. coli (EPEC)

Answer 19

Diarrhea in young animals
Attaching and Effacing lesions- characterizing histopathological lesion.
Actin pedestals–> pilus attaches to gut, TTSS induces actin pedestals.
Microvilli effaced/ disappear- very localized.
Get diarrhea due to loss of microvill and some of the effector proteins injected by TTSS alter electrolyte absorption.

Question 20

EPEC virulence factors

Answer 20

pathogenicity island–> locus of enterocyte effacement (LEE), TTSS

Question 21

E. Coli O157- VTEC/STEC/EHEC- general characteristics

Answer 21

EHEC important in humans, VTEC/STEC important in animals.

certain VTEC/STEC strains with vero toxin/shiga-like toxin cause hemorrhagic colitis in humans (EHEC)

Question 22

Shiga-like/vero toxin

Answer 22

SLT causes hemolytic uremic syndrome.

Question 23

VT/SLT toxins

Answer 23

both are AB subunit toxins
A subunit= enzymatic N-glycosidase–> inhibits protein synthesis, kills cells–> removes an adenine residue from the 3’ end of 28S rRNA. Prevents binding of aminoacyl t-RNA to the ribosome.
B= binding gangliosides Gb3 and Gb4–> main target=endothelial cells of BVs–> causes edema, hemorrhage and thrombosis.

Gangliosides Gb3 and Gb4 are present on renal cells and endothelium of BVs. SLT and VT are responsible for hemolytic uremic disease seen in EHEC in humans

Question 24

Hemorrhagic colitis

Answer 24

(more than 90% of EHEC cases)
-sudden onset of severe cramps and abdominal pain
bloody diarrhea after about 3 days
nausea or vomiting
little or no fever

Question 25

Hemolytic uremic syndrome

Answer 25

most commonly occurs in infection in children (50% of kids with HUS have to get dialysis).
15% of E. coli O157 infected people develop HUS due to SLT getting into blood
Causes: hemolytic anemia, thrombocytopenia, renal failure.
ABX may make HUS worse due to lysing of bacteria and release of even more toxin

Question 26

E. Coli O157

Answer 26

first isolated in 1982 in canada
found in hamburgers, raw potatoes, raw milk, unpasteurized fruit juices and cider, lettuce/alfalfa sprouts/salads and possibly sea eels in japan.
Around 100 organisms in healthy human is infectious dose.

Question 27

EHEC reservoirs

Answer 27

Mostly in last 5cm of cattle rectum
chickens, deer sheep and pigs
carrier animal isn’t sick
meat becomes contaminated during slaughter process
bacteria on cow’s udders and equipment can contaminate milk

Question 28

EHEC in certain countries

Answer 28

occurs more in developed countries (advanced foor production system); all other e.coli more often occur in developing countries.

Question 29

Evolution of E. Coli O157 and VT

Answer 29

E. coli O157 is like an EPEC that also produces VT. Where does the VT come from? Lysogenic phages.

Question 30

Virulence factors

Answer 30

LEE (locus of enterocyte effacement) is the pathogenicity island
VT1=shiga toxin
VT2 shares 56% homology with VT- often associated with severe e.coli but we don’t know why.

Question 31

EHEC pathogenesis

Answer 31

EPEC infection plus a toxin-induced infection. Displacement of microvilli, lesions cause diarrhea. The toxins produce HUS and hemorrhagic enteritis.

Question 32

Oedema disease in pigs

Answer 32

SLT/VT-2e, F18 fimbriae causes oedema (due to systemic release of SLT from gut) of forehead, stomach, LI and mesentery. No consistent evidence of enteritis, no LEE
Not zoonotic
Unique fimbriae bind to tissue.

Question 33

E. coli outbreak Germany 2011

Answer 33

May-July 2011
4000 people, mainly adults
20% of people infected came down with HUS
found to be E. coli O104:H4
different serotype- hybrid of 2 pathotypes
Hypothetically enteroaggregative E. coli plus VT genes

Question 34

EAEC+ VT genes

Answer 34

EAEC pathogenic in humans- causes chronic diarrhea in kids. This strain E. coli O104:H4 has acquired ST/VT from a phage. Get a number of organisms adhering, delivering lots of toxins which cause severe disease.