E.Coli

Question 1

What is E.Coli ?

Answer 1

A gram negative bacteria ( rod shaped ). Stains pink.

It is a constituent part of large bowel microbiota of many animals incl humans. This can possibly protect invasion by pathogenic species such as Salmonella.

• It is lactose-fermenting ( they use lactose as an energy source)
• They are facultatively anaerobic ( it can survive in both anaerobic and aerobic conditions , but prefers anaerobic conditions)
• they are motile

Question 2

What is E.Coli a marker of ?

Answer 2

A marker of faeces - if E.coli is found in water indicates faeces contamination

Question 3

How to identify E.Coli in the laboratory?

Answer 3

E.Coli and other enterobacteriacea can use sugar lactose as an energy source producing lactic acid as a waste product.

If you were to put E.coli onto a MaxConkey agar which contains lactose and a Ph indicator that goes red with acid Ph , then E.coli and other enterobacteriaceae grow as pink colonies on MacConkey agar because they would produce lactic acid.

And non-lactose fermenters would grow as yellow colonies.

Question 4

Why is E.coli considered to be diverse ?

Answer 4

There are many serotypes of E.coli - different E.coli strains have different antigens. We can indentify the different serotypes of E.Coli using a serological approach where we use antibodies to detect different bacterial surface antigens ( O , H , K ,F )

You can also profile E.coli based on their variation of biochemical pathways by metabolic profiling.

Question 5

What are common diseases that E.coli can cause ?

Answer 5

1. Intestinal infections ( diarrhoea )

2. Extra-intestinal infections : UTI , Bloodstream infections , neonatal infections.

Question 6

How does E.Coli cause diarrhoea ? ( enterotoxigenic E.coli ) ETEC

Answer 6

• Enterotoxigenic E.Coli ( one strain of E.Coli) which is an important cause of bacterial diarrhoea illness. It is the leading cause of travelers diarrhoea. And causes diarrhoea In young children and infants in developing countries.
• it has a feaco-oral transmission which means that we are basically eating foods / drinking things contaminated with faeces.
• this enterotoxigenic E.coli produces two toxins - a heat stable toxin (ST) and a heat Labile toxin ( LT). These toxins stimulate the lining of the intestines causing them to secrete excessive fluid producing profuse watery diarrhoea and abdominal cramping.
• ## onset 1-3 days after exposure and usually lasts 3-4 days.

Question 7

How does E.Coli cause UTI ?

Answer 7

Uropathogenic E.coli strains transfer from the rectum to the urethra and then migrate to the bladder.

Uropathogenic E. coli have a number of virulence factors :

• They have adhesins which facilitates adhesion or adherence to host cells which prevents clearance by mucosal secretions.
• toxins secreted such as Lipopolysaccharides ( this is a major component of the outer membrane of gram negative bacteria - it protects the bacteria from certain kinds of chemical attack)
• ## toxins such as A-Haemolysin is secreted which is a pore forming toxin.

Question 8

Why are women more prone to UTI than men ?

Answer 8

Because the distance between the anus and the bladder in women is much shorter than in men.

Question 9

What is the commonest cause of bacterial bloodstream infections ?

Answer 9

E.coli bacteria

Question 10

What are casual factors to E.coli bloodstream infections ?

Answer 10

• 50% of UTI’s can lead to bloodstream infections which is caused by ineffective antibiotic treatment.
  2. 21% of patients have urinary catheters

Question 11

How to prevent E.Coli infections from causing diarrhoea?

Answer 11

1. Avoid foods and drink that could be contaminated with bacterial
2. Prevent eating raw fruits and vegetables ( salads ) , raw seafoods or undercooked meat or poultry. Unpasteurised dairy products , food from street vendors , untreated water ( incl ice ) in areas lacking adequate chlorination.

Question 12

How to treat Diarrhoea caused by E.Coli ?

Answer 12

1. No specific treatment is usually required as the infection will recover in 3-4 days.
2. Clear liquids are recommended for persons with diarrhoea to prevent dehydration and loss of electrolytes.
3. Oral rehydration solutions.
4. Avoid antibiotics as this could make illness worse - some evidence has shown that this could make E. coli more toxic.

Question 13

How to treat UTI caused by E.Coli ?

Answer 13

Commonly used antibiotics are trimethoprim and nitrofurantoin

Nowadays , we need to give nitrofurantoin because 60% of E.Coli urine isolated tested in labs are trimethoprim resistant.

Question 14

What are the two common strains of E.Coli that cause diarrhoea?

Answer 14

1. Enterotoxigenic E.Coli ( ETEC)

2. Enteropathogenic E. coli ( EPEC)

Question 15

How does enteropathogenic E. coli cause diarrhoea?

Answer 15

X