If the bagged salad scare continues, produce farmers could face the same kind of financial trouble that threatened cattle ranchers in the 1990s. A 2003 article in in lost sales over the previous decade. Fortunately for lettuce producers, they can benefit from the science being pursued by beef farmers to save their industry. One such line of research is a vaccine to prevent cows from shedding virulent E. coli in their feces. Veterinarian David Smith at the University of Nebraska at Lincoln has spent five years testing this vaccine, which stimulates the production of antibodies against the proteins that the bacteria secrete to help them attach to the gut wall. Smith’s results show that the vaccine reduces the number of cattle shedding virulent E. coli in their feces by 65 percent. In December 2006, Bioniche Life Sciences, a Canadian pharmaceutical company, was granted a license by the Canadian Food Inspection Agency to distribute the vaccine to cattle veterinarians there. Approval is still pending in the United States.
(Courtesy of USDA/ARS)
Other approaches are more experimental. Todd Callaway, a microbiologist at the USDA Agricultural Research Service in College Station, Texas, has poked around in cattle feces to find an array of bacteriophages—viruses that attack bacteria—that target E. coli O157. In a recent study, he fed a cocktail of these viruses to sheep infected with the O157 bacteria and found a sharp reduction in the quantity of that strain of E. coli in their intestines. He is now investigating whether spraying the viruses onto cattle hides—a major source of infection in slaughterhouses—could also reduce their bacterial load.
Even if these prevention methods succeed, they are unlikely to be foolproof, so scientists are also developing new ways to attack rogue E. coli if they reach humans. One approach is to target the genes that make E. coli O157 so virulent. James Kaper has discovered that when the bacterial population reaches a critical mass in the large intestine, the microbes secrete hormonelike compounds. These compounds, in turn, switch on the genes that enable the bacteria to colonize the gut wall and to exude their toxin. Disrupting this bacterial groupthink could provide a way to prevent invasion. Vanessa Sperandio, Kaper’s former postdoc who now heads her own lab at the University of Texas Southwestern Medical Center in Dallas, has discovered three molecules that can block interbacterial signaling among E. coli. She plans shortly to begin animal testing of a drug derived from one of the three molecules.
Another option is to defang the shiga toxin itself, a tactic adopted by microbiologist Alison O’Brien of the Uniformed Services University in Bethesda, Maryland. She has created toxin-smothering antibodies that have been shown to be safe in humans by Caprion Pharmaceuticals, paving the way for efficacy trials. Such an antibody-based treatment would be most effective if administered soon after the onset of infection.
Ultimately, though, quashing the bacteria at their source—the
cows—is probably the most effective way to prevent E. coli O157
infections in humans. “This isn’t rocket science,” says DeWaal. “It’s
critically important that both human and animal waste be kept off
crops. It’s appropriate to have restrictions on the use of raw manure,
to have monitoring of composting processes to make sure they’re
effective, and to restrict the use of water that may contain treated
sewage.” But Kaper adds a caveat. “There are so many different bugs,
there are so many different types of foods, so many different ways in
which food is prepared and processed,” he says. “I don’t think the food
supply can be totally safe.”
