Rise of the Superbacteria

When Philip Tarr heard the first reports of a massive outbreak of E. coli in Europe recently, they had a sickeningly familiar ring. Tarr, a microbiologist at Washington University, is an expert on the strains of E. coli that have periodically wreaked havoc in the United States. In 2006, for example, E. coli on contaminated spinach infected 199 people in the United States, causing kidney failure in a number of cases. The European outbreak seemed to fit the pattern: people were infected with E. coli apparently after eating contaminated vegetables.

But then Tarr got a rude shock. German hospitals sent samples of the E. coli to the Beijing Genome Center to have their DNA sequenced. On June 2, the Chinese researchers reported that the strain was not the same E. coli that contaminated the spinach, known as O157:H7. In fact, it was an entirely different strain, called O104:H4, that had never been associated with epidemics before. Tarr searched the medical literature for reports of the European strain. He could find only a handful of people who had carried it, and none of them got sick. But somehow this obscure microbe had turned vicious, triggering one of the biggest—if not the biggest—E. coli epidemics in history, with at least 1,730 infections and 18 deaths (at time of writing).

“We didn’t know this bug was out there,” says Tarr. “This outbreak is taking us all by surprise.”

The fact that someone like Tarr has been taken by surprise should be of concern to everyone. The new epidemic raises grave questions about how prepared the United States and other countries are for a similar outbreak.

What makes these outbreaks particularly confusing is that E. coli is, for the most part, a harmless creature. We are each home to billions of harmless E. coli that dwell in our gut. They live peacefully in every other mammal, too. E. coli is so harmless, in fact, that microbiologists began to rear E. coli in laboratory flasks a century ago, and it became the best-studied species on earth.

But in the mid-1900s, scientists began uncovering strains of E. coli that could cause life-threatening diarrhea. Unlike ordinary E. coli, they carried genes for a poison known as Shiga toxin, named for Japanese bacteriologist Kiyoshi Shiga. Over time, microbiologists identified a number of strains of disease-causing bacteria, classifying them by the proteins on their surface. In 1982, E. coli O157:H7 burst on the scene with particularly grisly flair. It struck 25 people in Medford, Ore., and then three months later the same strain caused an outbreak in Traverse City, Mich. Scientists were able to trace the bacteria back to undercooked hamburgers.

Since then, scientists have found a half dozen other strains that cause similar illnesses, but E. coli O157:H7 has been responsible for the lion’s share of E. coli food poisoning. It struck again in 1993 in contaminated hamburgers in Washington state, for example, sickening 732 people and killing four of them. But it has not used just hamburger to infect its victims. Along with the spinach outbreak of 2006, E. coli O157:H7 has turned up in lettuce, bean sprouts, and even cookie dough.