Pathogens in perspective 2

Question 1

E. coli

Answer 1

Gram negative
Facultative anaerobe. Can switch to anaerobic in the gut
Many strains (sub groups with unique characteristics)
Different strains are host specific
Adheres to mucus of the large intestine

Question 2

E. coli virulence factors

Answer 2

Adhesins (fimbriae)
Invasins (haemolysin)
Motility (flagella)
Toxins (LT/ST, shiga, endotoxins)
Antiphagocytic properties (K antigens, capsules)
Bactericidal defence (LPS)
Genetic attributes (siderophores)

Question 3

E. coli serotypes

Answer 3

Recognised based on O, H and K antigens
O (lipopolysaccharide antigen)
F (fimbriae for attachment in early infection)
H (flagellum). Locomotion, sensory perception and pathogenicity
K (capsule)
O157:H7 most pathogenic

Question 4

ETEC

Answer 4

Enterotoxigenic E. coli
Non-invasive
Causes diarrhoea in humans and cattle (iron imbalances leading to water in gut)
Fimbrial adhesins to bind enterocyte cells in small intestine
LT and ST (cGMP accumulation in target cells and secretion of fluid into intestinal lumen) enterotoxins

Question 5

EAEC

Answer 5

Enteroaggregative E. coli
Only found in humans
Non-invasive
Binds intestinal mucosa to cause watery diarrhoea
Produce ST enterotoxin and haemolysin (bursts RBCs)

Question 6

EPEC

Answer 6

Enteropathogenic E. coli
Diarrhoea in humans, rabbits, dogs, cats
Lacks fimbriae, ST and LT toxins
Moderately invasive and elicit inflammatory response
Adhesin (intimin) to bind host intestinal cell. Causes rearrangement of actin in host cell

Question 7

EIEC

Answer 7

Enteroinvasive E. coli
Only found in humans
Diarrhoea and high fever
Invade epithelium from intestinal lumen through M cells
Phagocytosed by macrophages but can escape and induce apoptosis in the macrophage

Question 8

EIEC pathogenesis

Answer 8

Invasive genes carried in 140MDa plasmid
mxi and spa loci encode type III secretion apparatus (used to inject protein effectors into host cell)
IpaA secreted protein causes actin rearrangement and membrane ruffling to internalise bacteria
IpaB degrades vacuole to release bacteria into cytosol
VirG (IcsA) triggers actin polymerisation

Question 9

EHEC

Answer 9

Enterohaemorrhagic E. coli
Humans, cattle, goats
O157:H7 
Bloody diarrhoea but no fever
Can cause haemolytic-uremic syndrome

Question 10

E. coli O157:H7

Answer 10

Meat contaminated during animal slaughter/processing
Adheres to mucosa of gastrointestinal tract
Becomes resistant to stomach acid and proliferates
Shiga toxins enter blood stream and damage kidneys

Question 11

Haemolytic uremic syndrome

Answer 11

Acute complication causing renal failure
Haemolytic anaemia, acute renal failure and low platelet count
Kidney failure may also occur

Question 12

TTP

Answer 12

Thrombotic thrombocytopenic purpura
Same features as HUS
Can include CNS involvement and fever

Question 13

Aberdeenshire case

Answer 13

Scout camp in agricultural showground in 2000
300 sheep grazing beforehand
20 campers became ill. No deaths
E. coli spread via direct person to person contact and via faeces on land
O157:H7 can survive in soil for 15 weeks

Question 14

Lanarkshire case

Answer 14

O157:H7
21 people killed and 496 severely ill.
All cases linked to local butcher with improper separation of cooked and raw meat

Question 15

Germany case

Answer 15

O104:H4 outbreak
Shiga toxin (STEC) producing EAEC
3950 cases and 54 deaths.
22% of cases involved HUS
Linked to bean sprouts, cucumbers and fenugreek