In May, a form of the bacteria Escherichia coli (better known as E. coli) began infecting people in Germany and other parts of Europe. Now, with 18 dead and over 1,500 people infected, the World Health Organization (WHO) has announced that the strain responsible for the outbreak has never before been isolated from a human patient, making it a completely new strain.
Designated as 0104:H4, the new E. coli strain combines two particularly dangerous elements — toxin and “glue.” Genetic analysis has shown that the strain is in a class of E. coli called STEC that produces Shiga toxin, which causes diarrhea and vomiting. In severe cases, it can also cause hemolytic uremic syndrome (HUS) by attacking the kidneys and causing subsequent coma, seizure, and stroke.
Researchers believe that like other STEC’s, this strain contains a “glue” or protein that helps the bacteria cling to the cells in the intestine. The ability to stick to intestine cells makes it harder for the body to get rid of the bacteria, so it remains in the body, producing toxins longer. But the German strain doesn’t contain the same glue as other STEC’s. The eae gene, which codes for an adhesion protein in STEC’s, is absent in the German strain.
The German outbreak has largely affected more adults and women, but E. coli outbreaks typically affect more children, and do not favor one gender over the other. The absence of the eae gene in the German strain may suggest that the gene plays a role in who the bacteria infect, because it is present in other STECs that infect mostly children.
Germany has reported 470 cases of HUS caused by the current outbreak. Previously, the largest outbreak of E. coli infection in Germany in 1993 caused 44 cases of HUS. Researchers believe the combination of toxin production and stickiness, in addition to the prevalence in adults, may be the force behind the severity of this outbreak.
However, the unique properties of this E. coli strain don’t end at mysterious stickiness or adult infection. This strain is also antibiotic resistant. Patients suffering from an E. coli infection are not typically treated with antibiotics, because the drugs can spark the bacteria to increase Shiga toxin production. But, the antibiotic resistance of the strain may prolong the outbreak by helping the bacteria survive in its environment.
Making matters worse is the inability of officials to identify the source of the outbreak. A study of patients conducted by the Robert Koch Institute found that adult women often ate raw vegetables prior to experiencing illness. However, while produce is the main suspect, no particular item has been identified as a cause. Early reports claimed cucumbers from Spain were the culprit, but subsequent testing has shown that while those particular cucumbers were carrying E. coli bacteria, it was not the strain causing the German outbreak.
The WHO has cautioned the public against assuming that produce is to blame. According to Flemming Scheutz, head of the WHO Collaborative Center for Reference and Research on Escherichia and Klebsiella in Copenhagen, the new strain could have originated in an animal and been passed directly from the environment to humans.
Researchers hope that further analysis of the genome of the 0104:H4 strain will help them understand what gives this strain its adhesive ability, and how this may be connected to the virulence of the strain in adults and women.