Enterohaemorrhagic Escherichia coli EHEC

Biology

Habitat and transmission: In most cases, E. coli is non-pathogenic and lives commensally in the intestines of humans and animals. However, pathogenic varieties of E. coli such as EHEC pathotypes can cause serious disease, in this case, through the production of shiga toxins. EHEC is a cause of waterborne and foodborne illness and is spread via the faecal-oral route. E. coli O157:H7 is the most commonly known epidemic strain. However, in March 2011 an epidemic outbreak of E. coli O101:H4 originated in Germany that caused thousands of EHEC infections, 877 cases of haemolytic uraemic syndrome (HUS) and 32 deaths (Rubino et al., 2011). It is thought that the source of the O104:H4 strain was contaminated raw vegetables and sprouted seeds (Rubino et al., 2011). However, other common sources of EHEC include contaminated water, ground meats, unpasteurised milk, fruits, vegetables and salad leaves washed in contaminated water or through person-to-person contact (Karmali, 2004). EHEC is also a frequent cause of foodborne diarrhoeal disease for travellers (Travellers’ diarrhoea).

Treatment and antibiotic resistance: Antibiotic usage in EHEC infections is a controversial and there is no specific treatment available for HUS.(Karmali, 2004). Indeed, EHEC have been shown to produce more toxins when exposed to sub-lethal concentrations of antibiotics, therefore antibiotics should be avoided at the diarrhoeal phase of HUS/EHEC infection (Scherling et al., 2008). New neutralising compounds and antibodies that specifically target EHEC toxins are currently in trial (Scherling et al., 2008; Mohawk et al., 2010).

Prevention and control: As EHEC is commonly associated with traveller’s diarrhoea it is necessary to ensure that food is cooked thoroughly and water is safe to drink. Good sanitation is also vitally important in reducing transmission of EHEC strains. Healthcare workers should employ good hand hygiene, particularly when fitting catheters, to minimise the risk of infection.

Symptoms/Effects

Disease and symptoms: EHEC causes disease through the production of shiga toxins. EHEC can produce at least four types of bacteriophage-mediated cytotoxins; Stx1, Stx 2, Stx 2c and Stx 2d (Karmali, 2004). The infectious dose is thought to be around 100 microorganisms or fewer (Karmali, 2004). The incubation period of infection is anywhere between 3-5 days after which the affected individual might experience abdominal cramping followed by watery diarrhoea. This can lead to haemorrhagic colitis and bloody diarrhoea presentation. Haemolytic uraemic syndrome (HUS) can also occur in severe cases of EHEC infection. EHEC-mediated HUS has been shown to lead to permanent renal failure and even death.

Technical

References:
Karmali M.A. (2004) Infection by shiga toxin-producing Escherichia coli. An overview. Mol Biotechnol. 26(2): 117-122.

Mohawk K.L., Melton-Celsa A.R., Robinson C.M. and O’Brien, A.D. (2010) Neutralizing antibodies to shiga toxin type 2 (Stx 2) reduce colonisation of mice by stx-2 expressing Escherichia coli O157:H7. Vaccine. 28(30): 4777-4785.

Rubino S., Cappuccinelli P. and Kelvin D.J. (2011) Escherichia coli (STEC) serotype O104 outbreak causing haemolytic uraemic syndrome (HUS) in Germany and France. J Infect Dev Ctries. 5(6): 437-440.