30: E. Coli and Salmonella

Question 1

characteristics of escherichia coli

Answer 1

gram-negative bacillus (rod)

many flagella

grows very fast
- 20-minute doubling time

Question 2

remarkably diverse organism

Answer 2

core genome with 2167 genes

average genome with 4721 genes

total number of possible genes as 10131

constant exchange of genetic material between bacteria

Question 3

how many pathovars of pathogenic e. coli?

Answer 3

8

variations based on where they infect humans

Question 4

e. coli statistics

Answer 4

400M infections annually worldwide

Question 5

EPEC

Answer 5

around a long time

causes childhood diarrhoea

transmits human-human
- not a zoonosis

fecal-oral transmission

no shiga toxin

Question 6

EHEC/STEC

Answer 6

food/water-borne pathogen in industrialised countries with agriculture

zoonotic from cattle/animals
- not only from eating meat but exposure to cow feces

secreted shiga toxin can lead to haemolytic uremic syndrome (HUS)
- lyses RBC, clogs kidneys, leads to kidney failure

Question 7

EHEC/STEC statistics

Answer 7

265K illnesses annually in the US

3600 hospitalisations and 30 deaths

Question 8

where does the shiga toxin come from?

Answer 8

shigella

Question 9

similarities between EPEC and EHEC/STEC

Answer 9

share virulence determinants

same distinctive mechanism of intestinal colonisation

Question 10

attachment of EPEC and EHEC/STEC

Answer 10

secrete proteins allowing them to attach through pedestals

bacteria damage microvilli and create their own pedestals

triggers actin production in cells to induce this

Question 11

inducing pedestal formation

Answer 11

inject an e. coli receptor protein, Tir, into the epithelial cell which allows for attachment

recruits from actin so it’s a solid formation and bacteria stay attached indefinitely

Question 12

serotyping e. coli antigens

Answer 12

specific polysaccharide and flagellar proteins

polysaccharide side chains (O)

capsular antigen (K)

flagellar protein (H)

many e. coli serotypes and different antigens, so you need a lot of antibodies

Question 13

main EHEC/STEC serotype

Answer 13

O157H7 causes 90% of the disease

most frequently isolated from people in the US, UK and Japan

Question 14

EHEC/STEC shiga toxin

Answer 14

forms a pentameter of B subunits that bind and enter host cells, allowing a single A subunit to enter the cell

subunit A inhibits protein synthesis, leading to cell death

attacks epithelial cells, endothelial cells and immune cells
- bacteria allowed outside or into the blood stream

people usually die from kidney failure and systemic inflammation

antibodies are protective against severe disease

Question 15

EHEC/STEC outbreak at jack in the box in 1992

Answer 15

over 600 people sickened in 6 states (mostly children)
- 4 deaths, 50 cases of kidney failure

cause was knowingly undercooking burgers

USDA began testing beef for O157H7 in 1994
- can’t just test for e. coli because it’s everywhere

Question 16

how did EHEC come about?

Answer 16

shigella and shiga toxin gene on a plasmid taken up by a bacteriophage (viruses that infect bacteria)

mechanism of turning a commensal into a pathogen

Question 17

EHEC/STEC transmission in animals

Answer 17

healthy cattle as major reservoirs of O157H7 with no symptoms
- contaminated bovine products and crops as predominant sources for human infections

5% of dairy cows carry EHEC

cow super-shedders exist
- remain infected for long periods of time
- may shed more than 95% of e. coli in a herd of 100

Question 18

EHEC/STEC human transmission

Answer 18

anything coming into contact with cow feces

undercooked/unpasteurised animal products

contaminated food/water/soil

Question 19

EHEC/STEC disease in humans

Answer 19

hermorrhagic colitis
- blood diarrhoea from intestinal bleeding
- abdominal cramps
- fever, nausea, vomiting
- mostly self-limiting and resolve in a week

haemolytic uremic syndrome
- most deaths in humans
- kidney failure, anemia, etc.

Question 20

EHEC/STEC treatment

Answer 20

mainly supportive

antibiotics avoided since they may not reduce symptoms or prevent complications
- doesn’t work against toxins and only bacteria so if bacteria already replicated and produced toxin, too late for antibiotics

Question 21

salmonella enterica serovars

Answer 21

2 main servovars

s. typhimurium

s. typhi

Question 22

s. typhimurium

Answer 22

disease - gastroenteritis

duration - short-term infection of GI tract

host range - broad range of humans/animals

global burden - 78M infections and 59K deaths

Question 23

s. typhi

Answer 23

disease - typhoid fever
- much more severe

duration - life-threatening systemic infection, life-long chronic infection
- 3-5% are carriers shedding high levels

host-range - human specific

global burden - 11M infections and 28K deaths

Question 24

how does salmonella cause disease?

Answer 24

comes in and lives on the intestinal wall and inside epithelial cells

goes across tissues, lives in RBC

Question 25

chronic s. typhi and bacterial evasion

Answer 25

inhibits antibody binding and complement

blocks LPS and flagellin binding to TLRs

toxin kills cells and inhibits neutrophils

Question 26

s. typhi virulence factors

Answer 26

can infect/replicate intracellularly and extracellularly

huge advantage
- evades antibodies inside, produces toxins outside to spread across the body