O157:H7 and O104:H4 Vero/Shiga toxin-producing Escherichia coli outbreaks: respective role of cattle and humans

1. Introduction2. Verotoxin-producing and enteroaggregative E. coli2.1. Verotoxin-producing E. coli with attaching and effacing properties2.2. Verotoxin-producing E. coli without attaching and effacing properties2.3. Enteroaggregative E. coli3. The O104:H4 as compared to O157:H7 Verotoxin-producing E. coli outbreaks3.1. Characteristics of the O104:H4 E. coli strain3.2. Reservoirs and transmission3.3. Clinical and epidemiological data4. Virulence factors and host specificity of AE-VTEC and Agg-VTEC4.1. The Verotoxins4.2. The AE lesion4.3. The AAF adhesins5. General discussion6. Competing interests7. Authors' contributions8. ReferencesEscherichia coli is a well-known Gram-negative, rod-shaped bacterium belonging to the family Enterobacteriaceae that readily grows on simple bacteriological media. While many strains occur as commensal members of the microbiota in the intestinal tract of animals and humans, some strains are, however, important pathogens, that cause a wide spectrum of diseases, ranging from self-limiting to life-threatening intestinal and extra-intestinal illnesses, like enteritis, enterotoxaemia, cystitis, pyelonephritis, meningitis, mastitis, arthritis, and septicaemia [1-3].Many pathogenic E. coli are host-adapted and only a limited number of strains infecting animals are able to cause disease in humans. These strains, however, are more likely to get the attention of the scientific community and of the news media. A typical example of zoonotic E. coli is the O157:H7 serotype that can be responsible for two severe syndromes in humans, haemorrhagic colitis (HC) and haemolytic uremic syndrome (HUS), and whose reservoir is the intestinal tract of healthy cattle and other ruminants [1,4,5]. The hallmark of these "enterohaemorrhagic E. coli" ("EHEC") strains is the production of cytotoxins called Vero(cyto)toxins (Vtx) or Shiga toxins (Stx), two synonyms for the same group of toxins referring either to their toxicity for Vero cells [6] or to their homology w