Updating on enteric collibacilosis in calves | Le point des connaissances sur les enterites a Escherichia coli chez le veau

This manuscript is a review article of the recently acquired knowledge on the various pathogenic Escherichia coli in cattle: enterotoxigenic strains (ETEC), enteropathogenic strains (EPEC), enterohaemorrhagic strains (EHEC), verotoxigenic strains (VTEC), and necrotoxigenic strains (NTEC). If the knowledge on ETEC, which produce a heat-stable enterotoxin (STa) and one or two fimbrial adhesins (F5, F41) has no more really progressed recently, the knowledge on the other strains has progressed a lot during the recent ten years. It has indeed been confirmed that EPEC and EHEC strains cause enteritis and diarrhea mainly in two to eight week-old calves. Their main and common virulence property is the effacement of the enterocyte microvilli and the intimate attachment to the enterocyte cytoplasmic membrane whereas the verotoxins produced by EHEC are responsible for the occurrence of blood in the feces (haemorrhagic enteritis). However their initial colonization factor is still unidentified, if any. On the other hand the role of VTEC, which produce only verotoxins, in the occurrence of disease is still controversial. NTEC also produce different toxins (Cytotoxic Necrotoxing Factors, Cytolethal Distending Toxins) and adhesins (P, S, and/or F17 fimbrial and/or Afa-VIII afimbrial adhesins) and are subdivided into NTEC1 and NTEC2, which are responsible for intestinal and invasive diseases. The roles of these toxins and adhesins are currently under investigation in cell cultures (in vitro models) and in animals (in vivo models). If ETEC are considered as primary pathogens in calves, EPEC, EHEC and NTEC are regarded more as opportunistic pathogens, waiting for favorable environmental circumstances to cause pathologies. Right now only vaccines to ETEC have been studied and are commercialized. A more fundamental conclusion is that some Escherichia coli strains became pathogenic after acquisition of "foreign" genes, located on mobile genetic structures: plasmids, transposons, phages, and pathogenicity islands; as an illustration of the extreme plasticity of the bacterial genome.