Importance of Escherichia coli strains producing verotoxins
The production of a heat-labile protein unrelated to cholera toxin was described in the 1960s in studies of Escherichia coli isolated from animals. However, it was not until 1982 when Riley et al. reported an outbreak of haemorrhagic colitis associated with an E. coli that produced the same heat-labile toxin, and that these strains were considered hazardous to humans. A second interesting outcome of the study by Riley et al. was that E. coli strains isolated during this outbreak belonged to a serotype that had not been previously associated with human disease. Over the subsequent years, this 'new' serotype, O157:H7, became the predominant causal pathogen worldwide for both haemorrhagic colitis and haemolytic-uraemic syndrome. Outbreaks of haemorrhagic colitis and haemolytic-uraemic syndrome associated with O157:H7 E. coli strains have been reported in Canada, the United States, Europe, and Japan.