E. coli O157:H7—Searching for Solutions

Escherichia coli —a bacterium that started out as a threat in ground beef—now shows up in raw vegetables, unpasteurized juice and milk, and even in the water we swim in or we drink from wells.

Millions of pounds of “contaminated” ground beef have been recalled based on detecting O157:H7 in a single sample from a production lot, raising the question of the efficacy and wisdom of end-product testing. The school lunch program faces a shortfall in available ground beef. The meat industry has come under attack by consumer activists and the federal government. New science-based systems of inspection have been tried and come under attack, even indirectly by the courts.

Scientists tell us that O157:H7 can adapt to hostile environments, and that consuming only a few organisms can cause disease. The responsibility for illness now falls fully on industry, responsibility for fixing the problem falls on government and industry, and little, if any, responsibility falls on the consumer.

Is O157:H7 a terror bug? It certainly has been for the meat processing industry, and the sprout and unpasteurized juice industries as well. New rules are rapidly forced on old industries, and, besides regulatory sanctions, litigation is a constant threat. Consumers have lost substantial confidence in the food supply. To the parents of the children who are most often the victims of O157:H7’s worst effects, it truly is a terror bug.

The first U.S. outbreak of O157:H7 associated with ground beef occurred in 1982. It was not until 1993, following another ground beef–associated outbreak that concerted research efforts were focused on O157:H7. Thus, a decade of opportunity to solve the problem was lost, and O157:H7 was given a decade to further adapt to the host(s) and environment, and spread.

Much about the rapid rise of O157:H7 could have been predicted from studies on the salmonellae. Salmonellae are among the ultimate survivors, some having adapted specifically to one or a limited number of animal hosts, yet capable of surviving well in harsh environments. Specific salmonellae are well known to cause human illness at extremely low doses. Should we have been surprised then by the emergence of O157:H7? The concept of virulence is changing, such that virulence and survival are becoming somewhat synonymous. If O157:H7’s genetic repertoire has evolved such that the microbe is extremely successful at adaptation, should we not expect that the same, or similar, repertoires will appear soon and in other genera?

It is an unfortunate truth that we often must learn from an outbreak how to minimize the chance of another outbreak. If the causative agent has multiple environmental sources, it may take multiple outbreaks before most of the knowledge gaps are bridged. If the organism is adapting to new environments, more outbreaks may occur before the adaptation is characterized and preventive measures devised. That seems to describe how we arrived where we are with O157:H7, and it will likely be the scenario for other foodborne pathogens as they emerge.

Are there possible or available answers to the O157:H7 problem? If the lessons of history hold true now, testing end product, whether for O157:H7 or an indicator organism, is not the answer. What is an adequate sample size, if only a few organisms can cause illness and the pathogen is nonhomogeneously distributed? Cooking is an answer, but only if temperature is monitored, and consumers are not accustomed to monitoring the temperature of hamburgers. Preventing contamination of carcasses with fecal material or hide contaminants is an answer, but not an absolute certainty, no matter how much care is taken. Vaccines for eliminating O157:H7 from cows are being developed. While that is hopeful, we know that other domestic and wild animals harbor O157:H7. Vaccines for humans, particularly aimed at preventing renal damage, are a possibility, especially now that the recently characterized type III secretion system of O157:H7 and the longer-known shiga-like toxin may provide more targets, and since quorum sensing is thought to play a role as well.

Irradiation is available now. It is safe and effective. Many arguments have been made against it, and a few are worth mentioning. One fear is that industry will become lax, and that we will be irradiating inferior products. That issue can be dealt with. Some consumers fear what irradiation does to the product, and that fear has been fanned by certain activist groups, even though science has proven the process to be safe. Some believe that if irradiation is used now, it will always be used, and that industry will allow raw materials to further deteriorate as they gain more experience and comfort with irradiation and its possible ability to “fix” quality problems as well as destroy pathogens.

Why can’t irradiation be looked on as an interim solution to a problem that is waiting for other solutions to catch up? If but a fraction of the energy used to scare the public were used to educate the public about irradiation, including the inestimable value in paying 1/2 to 2 cents more per pound for ground beef, or another food vehicle, we might have a solution to the O157:H7 problem now.

by Douglas L. Archer is Professor and Chair, Food Science and Human Nutrition Dept., University of Florida, Gainesville.