Nontoxigenic sorbitol-fermenting Escherichia coli O157 : H- associated with a family outbreak of diarrhoea

A recent study from Germany reported the isolation of E. coli O157:H7/H- fr om patients with nonbloody diarrhoea and hemolytic uremic syndrome, questio ning the role of Shiga toxin as the main trait of virulence for human disea se. We isolated 6 sorbitol-fermenting E. coli O157:H- strains that do not c ontain Shiga toxin genes. The isolates originated from an outbreak (3 patie nts, 3 asymptomatic contacts) of non-bloody diarrhoea affecting two familie s sharing one household. Two children (age 10 months and 2 years) suffered severe diarrhoea over 30 and 10 days, respectively. Their uncle had moderat e diarrhoea for 2 weeks. In contrast to the other isolates, the uncle's str ain (EH109) did not harbour a chromosomal eae gene encoding gamma-intimin n or the plasmid gene E-hly; it also showed a PFGE pattern that was different from the unique pattern of the other isolates. Employing PFGE, phage typin g, and P-gene typing, five of the six six negative isolates were indistingu ishable from the six 2 positive "Bavarian outbreak strain". The only human serum tested, obtained from one asymptomatic contact, contained antibodies to the O157 lipopolysaccharide antigen. Our finding of five six negative so rbitol-fermenting E. coli O157:H- isolates (harbouring eae and E-hly) assoc iated with an outbreak of nonbloody diarrhoea supports the hypothesis that Stx production is not obligatory for the pathogenicity of E. coli O157 for humans.