Virulence of the Shiga Toxin Type 2-Expressing Escherichia coli O104:H4 German Outbreak Isolate in Two Animal Models

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Abstract
In May 2011, a large food-borne outbreak was traced to an unusual O104:H4 enteroaggregative Escherichia coli (EAEC) strain that produced Shiga toxin (Stx) type 2 (Stx2). We developed a mouse model to study the pathogenesis and treatment for this strain and examined the virulence of the isolate for Dutch belted rabbits. O104:H4 strain C227-11 was gavaged into C57BL/6 mice at 10 9 to 10 11 CFU/animal. The infected animals were then given water with ampicillin (Amp; 5 g/liter) ad libitum . The C227-11-infected, Amp-treated C57BL/6 mice exhibited both morbidity and mortality. Kidneys from mice infected with C227-11 showed acute tubular necrosis, a finding seen in mice infected with typical Stx-producing E. coli . We provided anti-Stx2 antibody after infection and found that all of the antibody-treated mice gained more weight than untreated mice and, in another study, that all of the antibody-treated animals lived, whereas 3/8 phosphate-buffered saline-treated mice died. We further compared the pathogenesis of C227-11 with that of an Stx-negative (Stx − ) O104:H4 isolate, C734-09, and an Stx2 − phage-cured derivative of C227-11. Whereas C227-11-infected animals lost weight or gained less weight over the course of infection and died, mice infected with either of the Stx − isolates did not lose weight and only one mouse died. When the Stx-positive (Stx + ) and Stx2 − O104:H4 strains were compared in rabbits, greater morbidity and mortality were observed in rabbits infected with the Stx2 + isolates than the Stx2 − isolates. In conclusion, we describe two animal models for EAEC pathogenesis, and these studies show that Stx2 is responsible for most of the virulence observed in C227-11-infected mice and rabbits.

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