Escherichia coli 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

Abstract

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