<i>Escherichia coli</i> O157:H7 and O157:H ⁻ Strains That Do Not Produce Shiga Toxin: Phenotypic and Genetic Characterization of Isolates Associated with Diarrhea and Hemolytic-Uremic Syndrome

<jats:title>ABSTRACT</jats:title> <jats:p> We have isolated one sorbitol-nonfermenting (SNF) <jats:italic>Escherichia coli</jats:italic> O157:H7 isolate and five sorbitol-fermenting (SF) <jats:italic>E. coli</jats:italic> O157:H <jats:sup>−</jats:sup> isolates that do not contain Shiga toxin (Stx) genes ( <jats:italic>stx</jats:italic> ). Isolates originated from patients with diarrhea ( <jats:italic>n</jats:italic> = 4) and hemolytic-uremic syndrome (HUS) ( <jats:italic>n</jats:italic> = 2). All isolates harbored a chromosomal <jats:italic>eae</jats:italic> gene encoding gamma-intimin as well as the plasmid genes E- <jats:italic>hly</jats:italic> and <jats:italic>etp</jats:italic> . The <jats:italic>E. coli</jats:italic> O157:H7 isolate was <jats:italic>katP</jats:italic> and <jats:italic>espP</jats:italic> positive. Respective sera obtained from the patient with HUS contained antibodies to the O157 lipopolysaccharide antigen. The <jats:italic>stx</jats:italic> -negative <jats:italic>E. coli</jats:italic> O157:H7 isolate is genetically related to <jats:italic>stx</jats:italic> -positive SNF <jats:italic>E. coli</jats:italic> O157:H7. All <jats:italic>stx</jats:italic> -negative SF <jats:italic>E. coli</jats:italic> O157:H <jats:sup>−</jats:sup> isolates belong to the same genetic cluster and are closely related to <jats:italic>stx</jats:italic> -positive SF <jats:italic>E. coli</jats:italic> O157:H <jats:sup>−</jats:sup> isolates. Our data indicate that <jats:italic>stx</jats:italic> -negative <jats:italic>E. coli</jats:italic> O157:H7/H <jats:sup>−</jats:sup> variants may occur at a low frequency and cannot be recognized by diagnostic methods that target Stx. </jats:p>