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A Quarter-Century of Research Advances in Tackling E. coli
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Over the last 20-plus years, beef researchers have had to shift their focus to get at the root of a serious problem with a toxic strain of E. coli (Escherichia coli), bacteria that live in the gut of all warm-blooded animals, birds and humans. The research was instrumental in developing ways to significantly reduce the incidents of illness and death in humans.
“Most E. coli are harmless and some are even beneficial, but a small portion of Shiga toxin-producing E. coli will cause damage in humans,” says Dr. Xianqin Yang, a research scientist in meat microbiology at Agriculture and Agri-Food Canada’s Lacombe, Alberta facility. “And different from a lot of other bacteria, very small amounts of the 0157:H7 strain can cause disease in humans.”
Dr. Xianqin Yang, research scientist in meat microbiology at AAFC Lacombe
Compounding the problem is that beef cattle don’t get sick from carrying the deadly bacteria.
“Ruminants are natural reservoirs for the bacteria – they may have it, but you cannot tell,” she says. “They carry the bug with them into the meat plants.”
The bacteria can’t be completely eliminated from incoming animals using the tools that are currently available, but great strides have been made.
The bacteria can be present on the surface of the hide or in the gut of the animal.
“Initially, since researchers knew that the E. coli 0157:H7 that turned up in beef had most likely originated in the cattle, they concentrated on stopping it at the source – the animal,” says Dr. Reynold Bergen, Beef Cattle Research Council’s (BCRC) science director.
He says that there was a lot of research that looked into changing the diet of cattle – such things as switching them from grain to forage before slaughter or using phages to attack the bacteria in the cow.
Dr. Bergen says that BCRC funded research into phages, but the bacteria would eventually evolve to resist them. It also funded vaccine research, but since the cattle didn’t present as sick, it was tough to develop an immune response.
Phages, or formally bacteriophages, are viruses that target and kill bacteria. They are the most prevalent biological entity on earth.
Dr. Reynold Bergen, BCRC science director
“They were all good ideas, but none of them worked consistently enough to solve the problem,” he says.
The biggest problem with concentrating on the animals was sheer numbers.
“There are millions of cattle on thousands of farms, and that makes it very difficult,” he says. Rather than trying to solve the problem at millions of different sources, maybe it would be more efficient to tackle it at a few key bottlenecks in the processing chain.
Pivoting to tackle the problem
The problem was very serious. At its peak in Canada in 1999, one in 12,500 Canadians had been infected with E. coli O157:H7 through food, water, travel, swimming and other sources, but that number came down to one in 147,059 by 2021.
That’s an impressive 90 percent decrease.
Source: Canada’s National Enteric Surveillance Program
According to Dr. Bergen, while consumer education about segregating raw meat and improved storage and refrigeration contributed to these results, the research, and subsequent changes to sanitation practices in meat plants, definitely reduced the amount of E. coli on beef, and therefore the risk of illness in humans.
During the mid-2000s, the research focus changed to the meat plant and reducing the transfer of the bacteria from the animal to the beef.
Technologies were developed to spray the hides to kill the bacteria. There were also advancements in methods for skinning the cattle. Dressing procedures were updated so the gut wouldn’t get punctured and possibly spread the bacteria to the beef. Steam pasteurization and lactic acid washes were also developed to clean the carcasses. Sanitation procedures were updated to ensure clean hands and knives and other equipment.
Back on the farm
Research has shown that E. coli 0157:H7 is prevalent in beef herds across Canada, regardless of their environment. Basically, the generally accepted idea is that if you have beef cattle, they have the bug.
For example, one study showed that 87.5 percent of beef calves in Saskatchewan had the 0157 antigen before weaning. Newly weaned calves are most likely to shed the bacteria and shedding is seasonal, peaking in the summer and early fall. While shedding usually only lasts about four weeks, the amount shed can vary, even within a day, and cattle can experience multiple bouts of it.
Dr. Cassidy Klima, technical director for the BCRC and the Canadian Cattle Association
“Using good on-farm food safety practices reduces the risk before the animals come into the plants,” says Dr. Cassidy Klima, technical director for BCRC and the Canadian Cattle Association.
Having good pens with clean bedding and good water drainage can minimize the potential for pathogens. Shipping the animals with minimal or no tags (clumps of mud and feces) on their bellies and legs to the packer also helps, as does having clean transport trailers.
A Canadian study showed that all hides of animals presented at slaughter were positive for Shiga toxin-producing E. coli. Further mingling during transportation could have contributed to this higher prevalence.
At the plant
“From the mid-2000s to now, they’ve (researchers) managed to reduce the incidence of E. coli from about 40 surviving on a carcass to four,” Dr. Bergen says.
But even that amount of E. coli 0157:H7 caused concern, given the fact that so little of the bacteria can cause serious illness.
“Colin Gill was two years into a five-year project the BCRC was funding to improve the carcass-focused methods and reduce the incidence even further but recognized that he and his team were working on the wrong problem,” says Dr. Bergen. Dr. Gill was employed by Agriculture and Agri-Food Canada as a research scientist at the Lacombe, Alberta facility, and Dr. Yang was on his team at the time.
“Initially, the thought was that the E. coli could be completely controlled during the dressing stage,” says Dr. Yang, who has done BCRC funded research into all three stages of meat processing – dressing, chilling, and fabrication.
“We found that, actually, most E. coli on meat is from equipment surfaces further along in the process,” she says.
Persistence and resistance
Dr. Yang’s most recent work focuses on the possibility that the bacteria could become resistant to heat and antimicrobials used in plants.
“What we found was that the E. coli are not more resistant in the meat plant than the E. coli that’s on cattle,” she says. “However, as they flow through from animals to meat on equipment surfaces, the amount of E. coli that were able to form biofilms increased.” Some bacteria can form biofilms which are structures that protect them from biocides and other treatments that might harm or kill them.
For the heat study, her team used a public database that holds close to 20,000 E. coli genomes to find out whether the E. coli that has the genetic marker for producing Shiga toxins also carry a genetic marker for heat resistance.
“Fortunately, there was none, so the possibility of a heat resistant 0157 is very low,” Dr. Yang says. This means that, for example, cooking hamburger to the recommended internal temperature of 71 degrees Celsius is sufficient to make it safe.
She says that the design of meat processing equipment makes it very difficult to get rid of all the bacteria and, going forward, she says that research will continue into better techniques for biofilm removal.
Despite the stubbornness of the E. coli problem, Dr. Yang reiterates that research and the sanitation practices put in place by processing plants have meant a significant drop in the incidents of E. coli disease from meat in humans, especially in the past 10 years.
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