Necrotoxigenic Escherichia coli type-2 invade and cause diarrhoea during experimental infection in colostrum-restricted newborn calves

There exists experimental evidence that necrotoxigenic Escherichia coli (NT EC) strains producing the cytotoxic necrotising factor 1 cause intestinal a nd extra-intestinal disease in piglets. On the other hand, no experimental model has been developed with NTEC strains producing the cytotoxic necrotis ing factor 2. In all, 14 colostrum-restricted calves were orally challenged with two strains isolated from the faeces of a diarrheic calf (B20a) or fr om the heart blood of a septicaemic calf (1404). All calves had diarrhoea w hich lasted until euthanasia in eight of them. In those calves, diarrhoea w as correlated with the faecal excretion of the challenge strains. At necrop sy, vascular congestion of the intestinal mucosa, hypertrophy of the mesent eric lymph nodes (MLN) and some congestion of the lungs were observed. Bact eriology confirmed the colonisation of the intestine by the challenge strai ns which were also recovered from the heart blood, the lungs and/or the liv er. Histological sections confirmed enterocolitis, lymphadenitis and limite d bronchopneumonia. In the intestinal tissue sections, bacteria testing pos itive in an in situ DNA hybridisation assay with a CNF2 probe were observed . Those results were confirmed by immunohistochemistry with a polyclonal an ti-O78 and a monoclonal anti-F17b antisera. Three of the five control calve s receiving either saline or a CNF-, F17a strain (25KH09) had no clinical s igns or lesions. The other two presented a profuse liquid diarrhoea but tho se calves were positive for the presence of K99(+) E. coli. In this model, both NTEC2 strains were thus, able to colonise the intestine, to cause long -lasting diarrhoea and to invade the blood stream with localisation in vari ous internal organs in colostrum-restricted conventional newborn calves. (C ) 2001 Elsevier Science B.V. All rights reserved.