Scientists Study Inoculating
Cattle Against E. Coli Germ

By Colleen Schreiber

SAN ANTONIO — E. coli 0157:H7 was first recognized in beef in 1982. Since that time it has created serious economic and political problems for the beef industry because most outbreaks of E. coli have been associated with cattle, either directly or indirectly.

Dr. Michael P. Doyle, a microbiologist with the University of Georgia’s Center for Food Safety and Quality Enhancement, spoke at the recent Plains Nutrition Council spring conference here. His topic dealt with four years of research in which he has focused on finding a method of eliminating this organism from cattle.

Since 1982, when the organism was first identified as a human pathogen, the leading vehicle for E. coli 0157 infections has been undercooked beef, Doyle told listening nutritionists. The second leading vector has been person to person transmission.

"We don’t need to ingest very many cells to get sick," he said. "It’s been suggested that ingesting 10 cells or less can produce illness."

The third leading vehicle has been vegetables, followed by drinking water, swimming water, raw milk, apple cider, etc. In 1995 some children became ill with E. coli after swimming in a state park in Rockford, Ill. The case control study revealed that the risk factor was associated with drinking lake water, Doyle said.

In almost all cases, he reiterated, the link has been made directly or indirectly to cattle. Checking some 12,000 feedlot cattle in 13 different states, researchers found that 1.6 percent were carrying E. coli 0157 and another .4 percent were carrying the "0157:nonmotile" strain, which can also cause sickness in humans. That suggests, Doyle said, that about two percent of feedlot cattle carry the organism.

Additionally, of 64 dairy cattle herds from 14 different states, 1.5 to 2.9 percent of animals between 24 hours of age and weaning and 4.9 to 5.3 percent of animals between the age of weaning and four months shed E. coli 0157 in their feces.

Doyle shared a report that he admitted may not be entirely scientific, "because it was done by the Democratic staff of the U.S. Senate." The report claimed that five tons of animal manure is produced for every person in the U.S. It also claims that animal manure is 130 times more plentiful than human waste, and that cattle, hogs, chickens and turkeys produced an estimated 1.37 million tons of manure in 1997.

Furthermore, he noted, EPA has identified agricultural runoff as the largest contributor of pollution in rivers and streams.

"The reason I even mention this is because manure is now being implicated as the vehicle of E. coli infections resulting from consumption of vegetables and swimming in recreational lakes," Doyle told listeners.

Scientists support that implication with incidents such as one in which a vegetarian who had grown all her own vegetables and had fertilized her garden with manure became infected with E. coli 0157. The same strain that was isolated in the woman was isolated in the soil in her garden.

A Centers for Disease Control study contends that the two most important risk factors for E. coli infection are eating undercooked hamburger meat and being associated with farm animals, particularly where cattle are present. A three year-old in the United Kingdom developed an E. coli infection after coming in contact with a dog on a farm. The same strain of E. coli found in the three year-old was also found in the cattle on the farm.

"This organism has a very low infectious dose; that’s why it’s so easily transmitted," Doyle told the group. Another likely contributing factor is that this strain of E. coli is highly tolerant of acidic conditions.

"They are uniquely resistant to acidity of the stomach, and that’s one of the first defenses the human body has in warding off bacterial infections," he stressed.

The illness attracts so much attention because the organism causes severe symptoms.

"It’s not just mild diarrhea. Many of the small kids who contract the organism develop kidney failure," he noted. "Additionally, about a third of the individuals have to be hospitalized and about 10 percent of the kids under 10 years of age develop renal failure. About half the patients who develop this kidney failure will require dialysis, about 75 percent will require blood transfusions, and about five percent of those cases will result in death."

Early on, it was believed that E. coli did not survive well outside the host organism. Studies conducted by Doyle and others, however, have found that isn’t necessarily the case. Research has shown that the colder it is up to freezing, the longer the organism will survive, Doyle said. His study found that the organism survived for about two months at refrigerator temperature, five degrees Celsius, almost two months at room temperature, and about a month and a half at body temperature. Other studies have indicated that some of the organisms can survive in other species for up to a year.

"It’s not the fragile organism that we once thought it was," Doyle concluded.

The microbiologist has been working for several years to find a way to reduce the problem. The first step was to determine where the organism primarily resides. Doyle said he was convinced that it largely resides in ruminants, cattle in particular.

The next step was to determine where the organism localizes in these ruminants. To determine that, he fed healthy calves E. coli 0157:H7.

"One of the first things we learned was that this organism isn’t pathogenic to cattle. It doesn’t produce any severe symptoms. In fact, cattle can be fed very large doses without any symptoms at all," Doyle said.

"We also found that once they ingest the organisms, the numbers decline very rapidly. Often it will clear the organism in a month or two, but it can stay at low levels for an indefinite period of time."

The organism is largely confined to the colon and the rumen, he said, but the rumen appears to be the most important site for long-term carriage of E. coli. He also learned that fasting the animal can increase the numbers of 0157 bacteria in the rumen.

Doyle then addressed the question of developing a vaccine that would be effective in preventing E. coli 0157. Canadian researchers have conducted studies in which animals developed an immune response after they were fed E. coli 0157, but once the bacteria passed through and the same animals were fed the same strain again, they still carried the harmful bacteria.

"That indicates that even though the animals exhibited a strong antibody response, the antibodies don’t protect the animal from reinfection," Doyle explained.

For that reason, the microbiologist sought a different approach. His research focused on isolating potential "probiotic" bacteria and then injecting healthy cattle to evaluate their efficacy in reducing the level of E. coli 0157:H7.

"Basically, we were looking for bacteria that will inhibit or kill E. coli 0157:H7," he explained. About 1200 different bacteria were screened through this process and Doyle came up with 18 potential probiotic bacteria.

These bacteria, he noted, came from cattle feces, the colon or small intestines in cattle. Of the 18, there were 13 different strains.

A selected group of these different strains were fed to cattle, which then were tested for E. coli. The results were encouraging. In this particular study, fecal shedding of E. coli 0157:H7 ranged from 25 to 32 days compared to 14 to 19 days in five of the six calves treated with probiotic bacteria, Doyle told the group. At necropsy, E. coli was recovered from the feces of only one of the six probiotic-treated animals, whereas it was recovered from all nine members of the control group.

The persistence of E. coli in one animal in the treated group, Doyle theorized, might be due to the apparent failure of probiotic bacteria to colonize in this animal. He added that he believes it is possible that greater protection or clearance can be conferred by multiple treatments with probiotic bacteria.

In a nutshell, Doyle said, the treatment of cattle with probiotic bacteria can reduce the level of carriage and fecal shedding of E. coli, and may thereby reduce environmental contamination with this pathogen. Reducing E. coli carriage in cattle, he added, should decrease the likelihood of meat, vegetables, fruit and water contamination, thereby decreasing the potential for food, water and environment-associated E. coli illness in humans.