‘Robust organism’ | Salmonella found in cattle’s lymph nodes is the newest threat the beef industry must conquer
BANFF, Alta. — The number of E. coli and listeria infections has dropped in recent years, but salmonella remains a constant threat.
“Salmonella is a pretty robust organism. It is one of the toughest pathogens we encounter,” food scientist Keith Warriner of Guelph University told a recent Alberta Beef Industry Conference in Banff.
“Regardless of all the efforts we have had, salmonella has been up there as the number one,” he said.
Salmonella is responsible for 25 percent of food borne deaths compared to one percent for E. coli O157:H7. It has been found in eggs, meats, sushi, tomatoes, spices and alfalfa sprouts.
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Vaccinations and improved practices from farms to processing facilities have effectively reduced E. coli contamination in the food supply, said animal scientist Brad Morgan, who is in charge of food safety for Zoetis, formerly called Pfizer Animal Health.
“In Canada and the U.S., we have made a tremendous amount of progress on E. coli O157:H7,” he said.
“We have done a great job on it, but we have got to start addressing salmonella.”
E. coli bacteria are found on surfaces and can be removed, but salmonella works its way inside animals and produce and must be addressed in a different way.
Salmonella found in cattle’s lymph nodes is the newest threat.
Some meat plants are removing lymph nodes, but the bovine lymphatic system is spread throughout the body with about 100 nodes on each side of the carcass.
Lymph nodes can end up in ground meat and be mixed together and further spread bacteria.
“We have to do something to get inside there before it is ground,” Morgan said.
One species of salmonella has as many as 2,500 strains.
“The salmonellas that we hear about with antibiotic resistance and the salmonellas that affect people who get sick and die, a lot of time you don’t find those inside the lymph node,” Morgan said in an interview.
“We are able to find 21 different salmonella in the lymph nodes.”
His company is working with government and university researchers to find ways to clear this bacteria at the cow-calf and feedlot level.
A vaccine is available, but it is used most often in the dairy industry with good results. Tests on feedlot manure showed a lower incidence when beef animals were vaccinated.
Another project is investigating whether biting and sucking insects such as horse flies may spread the disease. Researchers put salmonella on flies’ legs and have been able to find the same strain in an animal after it was bitten.
“We are obviously going to have to do some pesticide work also because it looks like they are a big vector,” Morgan said.
Insects may pick it up from water, other animals, manure or the air.
Salmonella can get into crops such as tomatoes when manure is spread on fields.
It can persist for a year on the soil and can easily get into food processing facilities and survive.
Warriner said salmonella is often associated with poultry and eggs.
About .06 percent of eggs carry salmonella but continue to be a problem because people don’t cook them thoroughly.
About 10 percent of pigs carry salmonella at some point in their lives, while cattle carry it .2 to .6 percent of the time and shed it at low levels.
However, ground beef levels could reach 10 percent after processing.
Poultry are vaccinated in Europe, but it is less common in North America. Other on-farm interventions include checking litter, air, water and workers’ clothing to prevent its spread.
Delivering antibiotics in feed is a controversial way to curb salmonella.
“People don’t like antibiotics in feed anymore. The big concern with salmonella at the moment isn’t the fact that it is there. The fact is, it is multiple drug resistant,” Warriner said at the conference held Feb. 20-22.
It has shown resistance to antimicrobials like quinolone, fluroquinolone, ciprofloxacin and nalidixic acid.
Researcher Theobold Smith first isolated salmonella enterica in 1885 from infected pigs. He named the bacteria after his supervisor, Dr. Daniel Salmon.
Salmonella has been responsible for serious illness and death in the past.
Typhoid fever is among the problem diseases, although Warriner said vaccination has almost eradicated it in developed countries.
