S10 E.coli

Question 1

What is the gram stain of E.coli?

Answer 1

Gram-negative rods (red/pink stain)

Question 2

What family of bacteria is E.coli part of?

Answer 2

Enterobacteriaceae

Question 3

Is E.coli anaerobic or aerobic? Motile or non-motile?

Answer 3

Anaerobic (but can also survive in aerobic conditions - facultative)

Motile

Question 4

What can E.coli use as an energy source? What does this mean it produces as a waste product?

Answer 4

Sugar lactose and so produces lactic acid as a waste product

Question 5

How can you identity E.coli in a lab?

Answer 5

Use MacConkey agar that contains lactose and a pH indicator (goes red when acidic pH) - so E.coli will grow as pink colonies on the agar

Question 6

How can you determine the type of E.coli?

Answer 6

• serology - antibodies to detect different bacterial surface antigens e.g. O, H, K, F
• metabolic profiling as there’s variation in biochemical pathways
• genomic diversity

Question 7

What do the, O, H, F and K antigens link to on an E.coli molecule?

Answer 7

O - LPS
H - Flagella
F - Fimbriae
K - Capsule

Question 8

Where is E.coli fond in the normal microbiota? What is it’s possible role?

Answer 8

In the large bowel of humans and other animals

Protect against invasion by pathogenic species such as Salmonella

Question 9

What can pathogenic strains of E.coli cause? Why does it cause infection?

Answer 9

• intestinal infections
• toxin-mediated disease
• extra-intestinal infections - UTI, intra-abdominal, biliary tract, blood stream, neonatal meningitis

Linked to the presence of virulence factors that different strains have

Question 10

What are the 6 types of diarrhoeagenic E.coli?

Answer 10

• enterotoxigenic E.coli (ETEC)
• eneterpoathogenic E.coli (EPEC)
• eneteraggregative E.coli (EAEC)
• enteroinvasive E.coli (EIEC)
• diffusely adherent E.coli (DAEC)
• shiga toxin-producing E.coli (STEC) - enterohaemorrhagic E.coli (EHEC)

Question 11

Which types of E.coli are most common causes of diarrhoea in young children? And most common in immunocompromised patients?

Answer 11

EPEC and EIEC

EAEC

Question 12

What two toxins does ETEC produce? What do they do?

Answer 12

• heat-stable toxin (ST)
• heat-labile toxin (LT)

They stimulate the lining of the intestines causing secretion of excessive fluid leading to lots of watery diarrhoea and abdominal cramping

Question 13

What is the onset time for ETEC and how long does it last?

Answer 13

Onset is 1-3 days

Lasts usually 3-4 days

Question 14

How does EPEC act?

Answer 14

Localised effacement/removal of microvilli and attaches to the host cell surface forming an attaching and effacing (A E) lesion. To do this it needs type III secretion machinery. This connection allows the bacteria to insert bacterial proteins, etc into the host cell. It activates signalling pathways in the host cell leading to reorganisation of the host actin cytoskeleton

Question 15

What does STEC cause?

Answer 15

Haemorrhagic colitis (bloody diarrhoea) and haemolytic uraemic syndrome (HUS) - a triad of acute renal failure, haemolytic anaemia and thrombocytopenia

Question 16

What is the molecular action of Shiga toxin (STEC)?

Answer 16

• B subunits of Shiga toxins bind to globotriaosylceramide (Gb3) on the host cell surface
• the toxin is endocytosed and transported to the Golgi apparatus and the ER
• during the transport, the A chain is cleaved into a small A2 fragments and an enzymatically active A1 fragment (kept together by disulphide bond until the toxin reaches the ER where the A1 fad net is released and translocations into the cytosol
• in the cytosol, the A1 part inactivates ribosomes and so inhibits protein synthesis, results in cell death

Question 17

What are extra-intentional pathogenic E.coli (ExPEC)? What are some of the virulence factors?

Answer 17

Strains of E.coli that are capable of causing disease outside the intestinal tract

• adhesions
• iron acquisition systems
• protectins and invasns
• toxins
• etc

Question 18

In which gender are UTIs most common? Why?

Answer 18

Women

Due to anatomical differences between men and women (distance between anus and bladder shorter in women than men)

Question 19

What are the virulence factors for UPEC?

Answer 19

• adhesins
• toxins - cytotoxic to epithelial cells in urinary tract
• iron acquisition - bacteria produce their own iron-complexing proteins (siderophores) to acquire iron as low iron in urinary tract

Question 20

What is the commonest cause of bacterial bloodstream infections in England?

Answer 20

E.coli

Question 21

What are causal factors of E.coli bloodstream infections?

Answer 21

• UTIs due to ineffective antibiotic treatment
• urinary catheters
• hepatobiliary infections
• gastric intestinal infections

Question 22

How do you prevent E.coli (diarrhoea) infections?

Answer 22

• avoid food and drink that could be contaminated with bacteria e.g raw fruits and vegetables, raw seafood, undercooked meat/poultry, unpasteurised dairy products, food from street vendors, untreated water in areas without chlorination

Question 23

How do you treat E.coli (diarrhoea) infections?

Answer 23

• most will recover in a few days without specific treatment
• clear liquids are recommended to prevent dehydration and loss of electrolytes
• oral rehydration solutions
• avoid antibiotics - can make it worse (causes bacteria to produce more toxin?)

Question 24

What antibiotics are used to treat urinary tract infections?

Answer 24

Treatment is largely empirical

• trimethoprim
• nitrofurantoin

Many strains are trimethoprim resistant

Question 25

What antibiotics are E.coli bloodstream infections resistant to? How does the resistance get passed on?

Answer 25

• 40-50% are resistant to co-amoxiclav
• increasing resistance to carbapenemase

Horizontal gene transfer