E. coli are Gram-negative, non-sporulating, facultative anaerobic bacilli. They can grow on a wide range of substrates and at temperatures ranging from below 15°C up to 45°C or even higher, as seen with certain laboratory strains (optimum temperature 37°C). Some strains are motile and possess flagella.
Amongst the pathogenic E. coli, Verotoxin-forming strains (STEC or VTEC) have gained importance in recent years. The group of enterohaemorrhagic E. coli (EHEC) with its highly pathogenic serovar O157:H7 strain is particularly interesting in this respect. The main sources of infection are contaminated, raw or insufficiently heated foods of animal origin, such as meat and dairy products. The reservoir for EHEC is the gut of ruminants. The microorganisms can enter food during the processing of meat and dairy products if hygienic conditions are inadequate. The drastic increase in the incidence of food contamination caused by E. coli O157 demands reliable and rapid methods of detection.
EHEC is capable of inducing life threatening illnesses, particularly in people with immune deficiency, young children and the elderly. Although the most common cause of EHEC is E. coli O157, other serotypes, such as O26, O45, O103, O111, O121, and O145, are also relatively frequent causes of infection.
Typical symptoms are severe abdominal pain and diarrhea, which is initially watery but often becomes bloody. These are occasionally accompanied by vomiting. The illness is usually self-limited and lasts for an average of 8 days. In up to 10% of all cases, kidney complications (so-called hemolytic-uremic syndrome or HUS) occur, which can lead to temporary or even permanent kidney damage. Neurological symptoms may also occur.