Abstract
Dear Sir—In the recent paper, Wetzel and LeJeune (2007) show the presence of non-toxigenic strains of otherwise typical Escherichia coli O157:H7 being present in multiple animal and environmental sources. These observations are in line with our earlier observations (Hornitzky et al. 2005), where we noted that cattle, especially if suffering from gastrointestinal disease, harboured strains of E. coli O111 which were indistinguishable from typical enterohaemorrhagic E. coli O111, apart from lacking the ability to produce Shiga toxin(s) and the absence of the stx-converting bacteriophage. Further, it was recently shown (Bielaszewska et al. 2007) that patients infected with enterohemorrhagic Escherichia coli (EHEC) O26 carry both toxigenic and non-toxigenic variants. The importance of these findings should not be underestimated, because in the diagnosis of EHEC infections only looking for stx-producing strains may well give misleading results and provide totally misleading answers of the epidemiological situation. In addition the potential virulence of these non-toxigenic strains must be considered in any disease or outbreak situation. If it is shown that animals such as cattle and sheep regularly harbour these non-toxigenic potential EHEC which acquire their stx-converting bacteriophages only under certain as yet undefined conditions, it throws a completely new light onto the epidemiology of EHEC infections. Karl Bettelheim Flat 5, Rosedale Lodge 220 Chase Side London N14 4PH United Kingdom E-mail: bettelheim@talktalk.net
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