Hybrid E. coli Strain Caused Outbreak in Germany

BERLINThe rare Escherichia coli O104:H4 strain responsible for the deadly European E. coli outbreak that killed nearly 40 people and sickened more than 3,800 is a clone that combines the virulence potentials of the Shiga toxin producing ability of enterohemorrhagic E. coli (EHEC) and the adherence abilities of enteroaggregative E. coli (EAEC), according to new findings published in The Lancet Infectious Diseases.

A German team led by Helge Karch from the University of Münster investigated the virulence profiles of the E. coli O104:H4 strain by analyzing 80 bacteria samples recovered from patients between May 23 and June 2. Samples were tested for the presence of Shiga-toxin-producing E. coli virulence genes and for virulence genes of other intestinal pathogenic E. coli. All samples were tested for underlying characteristics, such as the ability to adhere to cells similar to those that line the gut, and antibiotic susceptibility.

Researchers identified that all isolates were from the HUSEC041 clone (sequence type 678), first isolated from a patient with Hemolytic Uremic Syndrome (HUS) in Germany in 2001. Unusually, all isolates produced both the Shiga toxin (Stx2) typical of EHEC and the "stacked-brick" adherence pattern of aggregates characteristic of EAEC (a trait that enables bacteria to gather together and stick to the cells lining the gut). The outbreak isolates also had an extended-spectrum -lactamase (ESBL) antibiotic resistance profile rendering them resistant to all penicillins and cephalosporins but susceptible to carbapenems.

The enhanced adherence of this strain to intestinal epithelial cells might facilitate systemic absorption of Shiga toxin and could explain the high frequency of progression to HUS. Antibiotic resistance might also play a part if -lactam drugs used to treat the infection suppressed competing microbiota," they said. Although we lack an explanation for increased virulence, this outbreak tragically shows that blended virulence profiles in enteric pathogens introduced into susceptible populations can have serious consequences for infected people."

German officials have said contaminated bean sprouts from an organic farm in Northern Germany were most likely the source of the outbreak. Since May 2, EU Member States have confirmed more than 700 cases of HUS caused by the bacteria. HUS is usually observed in children under age 5; however, in this outbreak the great majority of cases are adults, with more than two-thirds being women.