Study: Some E. coli found to survive high cooking temperatures

June 09, 2016

With barbecue season in full swing, there may now be a reason to turn up the heat on your grill.

A group of researchers from the University of Alberta and China’s Huazhong Agricultural University found that cooking ground beef at the 160°F (71°C) temperature recommended by government officials in the U.S. and Canada, may not be hot enough to kill all the strains of Escherichia coli (E. coli).

E. coli, a bacteria that’s found in the gut of both animals and humans, is not always harmful. However, some strains, such as E. coli O121 and E. coli O157:H7, as well as other strains of Shiga toxin-producing E. coli, cause millions of illnesses, thousands of hospitalizations, and many deaths every year. They can also cause kidney failure and have been at the center of several food recalls throughout the past few decades.

Until now, food safety experts agreed that cooking meat to 160°F killed the potentially dangerous pathogens from your soon to be cheeseburger, but thanks to research lead by food microbiologist Lynn McMullen, all that could be changing.

“We’ve been hammering consumers for years to cook chicken properly, to handle it properly, and to do the same with ground beef, but still we seem to have these outbreaks of E. coli (attributed to hamburgers). Does this explain why? It might,” McMullen said in a recent article.

In fact, this troubling development was first recognized by researchers about eight years when McMullen and food microbiologist Michael Gänzle began studying the thermal destruction of bacteria and found that it can leave some survivor organisms behind.

In the study, one student discovered that an organism survived for 70 minutes at 60°C (140°F, the minimum temperature that is recommended for steak). Repeating the experiment, the student found the same results. She compared her results to other labs’ published survival values, and found that the bacteria cultured at the University of Alberta behaved differently,  as most E. coli bacteria die within a few seconds at that temperature.

Even more alarming, the scientists discovered that salt can increase the bacteria’s heat resistance, and some of the strains can survive pressure up to 87,000 pounds per square inch. (That is the standard for bacterial death in high pressure food processing.)

“These organisms aren’t supposed to survive, but every once in a while they do,” McMullen said. “We decided to find out why and looked at the genomes to see what was different.”

The researchers found a suite of genes, called the locus of heat resistance (LHR) that are found only in the highly heat-resistant strains of E. coli under wet conditions, as is in raw meat. This grouping exists in about 2% of all E. coli in the databases, in both the pathogenic strains and the harmless strains.

The research team is now trying to discover how prevalent this problem of occasional survival is, and they said they would like to figure out how often the pathogenic E. coli will survive in cooked meat. The current guidelines and recommendations for cooking meat may need to be changed, depending on their findings, the article explains.

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Category: Food Safety