Clinical signs, reproduction of attaching/effacing lesions, and enterocyteinvasion after oral inoculation of an O118 enterohaemorrhagic Escherichia coli in neonatal calves

Attaching and effacing (AE) lesions are produced among others by enteropath ogenic Escherichia coli and enterohaemorrhagic E, coli (EHEC), which differ s from the former by the product:ion of cytotoxins active on various cell c ultures, the verocytotoxins, or shigacytotoxins. EHEC are associated with d iarrhoea and dysentery in humans and in ruminants, mainly calves from two t o eight weeks of age. Clinical signs and/or lesions have been reproduced ex perimentally with EHEC strains belonging to serotypes O5:K4/Nm, O26:K-:H11, O111:Nm, and O157:H7 which are isolated from cattle and/or humans. The pur pose of this work was to develop an experimental model of infection in newb orn calves with a bovine EHEC strain isolated from a calf which of died of diarrhoea, and belonging to the O118:H16 serotype, which is also common to both cattle and humans. The bovine O118:H16 EHEC strain was able to coloniz e the gut of three newborn calves, and to induce diarrhoea twenty-four hour s after challenge and to produce AE lesions in the small and/or large intes tines. AE lesions were detected microscopically and ultrastructurally in th e small intestine of one calf and in the whole intestinal track of two calv es. Internalization of bacteria and also of pedestal-bacteria complex insid e of the enterocyte was observed in two of the three calves. The significan ce of this stage is unknown but may be related to the invasion of the calf by the bacteria. The challenge strain was isolated from the mesenteric lymp h nodes of the same two calves but not from other organs or from heart bloo d. No blood was observed in the faeces of any of the three calves, nor were any lesions in the internal organs, which may have been related to the pro duction of a verotoxin whose role is still unknown in cattle. (C) 2000 Edit ions scientifiques et medicales Elsevier SAS.