May 2, 2007

 

Scientists turn to vaccines to combat E.coli

 

 

Dr Shousun C. Szu, a scientist at the National Institutes of Health, says the best way to prevent people from being poisoned by deadly E. coli would be to vaccinate all infants against the bacteria while Canadian biotechnology executive Graeme McRae says it would be more practical to vaccinate cows instead.

 

Scientists have looked to vaccines to prevent or treat and food poisoning for people and cattle by the strain E. coli O157:H7 as there has been meagre success in fighting the pathogen.

 

Currently, the main approach to prevent contamination is through careful handling, rigorous inspections and government regulation.

 

Slaughterhouses have shown reduced contamination through practices like washing carcasses with hot water, steam or acids. Now the focus is on new procedures and regulations for the fresh-produce industry.

 

Some researchers say medical approaches could eventually supplement food-processing measures as the Food and Drug Administration (FDA) on April 12 bared plans to run clinical trials of drugs in treating E. coli infections.

 

On the animal side, a vaccine for cattle developed by McRae's company, Bioniche Life Sciences, was approved in December for veterinarians in Canada where studies have shown vaccine can reduce but not eradicate E. coli shed into manure.

 

Guy Loneragan, a veterinary epidemiologist at West Texas A&M University said the likelihood of the cows spreading the bacteria through its manure can be prevented through vaccination.

 

Other methods being tested include cattle antibiotics, an industrial chemical, bacterial-killing viruses and friendly bacteria to displace the evil ones.

 

The antibiotic neomycin has also been shown to reduce O157 levels in manure.  However, its use can raise concern of developing human pathogens resistant to the medicines.

 

Another approach being studied involves phages, viruses that infect and kill bacteria.

 

Experts say multiple approaches might be used in parallel, because no single approach works perfectly.

 

One hindrance though is that ranchers and feedlots may receive little incentives on such treatments as these procedures do not make cows grow faster nor healthy as O157 does not sicken the cows that have it.

 

Efforts to develop drugs and vaccines for people also face barriers as outbreaks are rare and sporadic and it would be difficult to test treatments in clinical trials.

 

Medical experts add it might be hard to diagnose the infection in time to intervene medically as any treatment would have to be very safe because it would be given to children and many people have improved from E. coli infection without any intervention.

 

Dr Szu said a better approach would be to inoculate people so their immune systems could dispense with the bacteria before they had a chance to multiply and release their toxin in the bloodstream.

 

She and colleagues have developed a vaccine made of the complex sugar that is on the surface of the bacteria, the very O-type polysaccharide that gives O157 its name. The sugar is linked to a protein taken from another bacterium to make it more potent in stimulating the immune system.

 

On the other hand, the cattle vaccine developed by Bioniche is based on the work of B. Brett Finlay of the University of British Columbia, who helped discover how O157 bacteria attach themselves to the cattle intestines, where they can then multiply.

 

The bacteria use a type of microscopic syringe to shoot proteins into the cells lining the intestine, and the cells erect a protein pedestal, to which the bacteria can bind.

 

The Bioniche vaccine consists of proteins involved in the attachment and the vaccine's way to fight E.coli is to make the antibodies from the cow's immune system attack the proteins to block the attachment. The bacteria could still pass through the cow and into manure. But if they could not colonize, their levels should remain low.

 

Tests at the University of Nebraska found that the vaccine has reduced by 70 percent the number of cows shedding O157 into their manure, said Rodney A. Moxley, a professor of veterinary science there.

 

McRae, who is also the president of Bioniche located in Belleville, Ontario, said the company would begin to distribute the vaccine in Canada in June or July after it increases manufacturing capacity and has been approved together with clear evidence that the vaccine works.

 

McRae said he hoped to obtain approval to sell the vaccine in the United States from the Agriculture Department this year. Feedlots would be charged no more than US$2.20 a dose, with two doses needed, he said.

 

Randall D. Huffman, vice president for scientific affairs at the American Meat Institute, which represents beef processors, said that the cost was unimportant but the issue rests on the vaccine which "might not be right for everyone,'' because it was not 100 percent effective.

 

Huffman however said the cost would be considered if the technology has been proven effective.

 

His organization and the National Cattlemen's Beef Association helped finance the research on the vaccine and other approaches to reducing the shedding of O157.

 

One approach already in use is probiotics, the idea that friendly bacteria fed to cattle will displace O157. The Nutrition Physiology Corporation in Guymon, Oklahoma, sells a feed additive with lactobacillus, the same type of bacterium used in yogurt. The additive is sold to aid cattle digestion, but some studies suggest that it also reduces O157 in manure.

 

An experimental approach is to feed cows sodium chlorate, a chemical used in the pulp and paper industry. This idea takes advantage of the fact that O157 has an enzyme that allows it to survive without oxygen, which is not true for most desirable bacteria. That enzyme will convert sodium chlorate to sodium chlorite, which poisons the pathogen.

 

Robin C. Anderson, a microbiologist for the Agriculture Department in College Station, Texas said this approach is like a "suicide pill to the E. coli" and the treatment did not harm the cow.

 

Eka Chemicals, which makes sodium chlorate for the paper industry, is working to obtain regulatory approval for a cattle treatment.

 

E. coli O157:H7 causes 75,000 cases of infection and 61 deaths in the United States each year, according to a 1999 estimate by the Centres for Disease Control and Prevention posted on its Web site. The actual number of confirmed cases has dropped since then, particularly in 2003 and 2004, but increased in 2005 and 2006, in part because of the outbreaks.