Fire up the grill this summer. Then turn it up a little more.
Researchers at the University of Alberta, led by Dr. Lynn McMullen and Dr. Michael Gänzle, have been heating up strains of E. coli that originated from meat processing plants. Their findings, first reported by the Edmonton Journal, will make you want to leave your burgers on the grill longer than usual.
Ground beef, they found, might not be completely E. coli-free at 160 degrees Fahrenheit, which is the recommended minimum cooking temperature in both the U.S. and Canada.
When Elena Dlusskaya, a graduate student in UAlberta’s Department of Agricultural, Food, and Nutritional Science, found a strain of E. coli that could survive at 140 degrees Fahrenheit for over an hour, neither McMullen nor Gänzle believed her, according to a report from the university. So they tried the experiment again. And again. But the E. coli didn’t flinch.
“These organisms aren’t supposed to survive, but every once in a while they do,” said McMullen. “So we decided to find out why. We looked at the genomes to see what was different.”
The research team identified a group of 16 genes in the lab’s heat-resistant strains. Known as the locus of heat resistance (LHR), this genetic grouping is found in roughly 2 percent of all known forms of E. coli, including pathological strains.
Further experiments showed that some strains containing LHR could even outlast the safe cooking temperature recommended by both the U.S. Department of Health and Human Services and Health Canada.
“We discovered that some strains of E.coli are very, very heat-resistant and they can survive cooking in a burger to 71 degrees Celsius [160 degrees Fahrenheit],” McMullen told CTV News.
The FDA’s Food Code currently instructs restaurants to heat ground beef to at least 155 degrees Fahrenheit for 15 seconds. The CDC, on the other hand, tells consumers to stick to a single, easy-to-follow standard: 160 degrees with no specific time attached.
Unless you use a cooking method more complex than grilling both sides, that often means giving up the dream of a perfectly pink, medium rare patty. As the USDA notes, many patties turn brown “well before” they reach 160 degrees Fahrenheit. On the other hand, some burgers can stay pink in the middle beyond that temperature depending on the meat’s pH level, pigment, and fat content. The only way to be sure is to use a meat thermometer—something that the vast majority of American home cooks fail to do.
After these latest UAlberta findings, a meat thermometer is looking like an increasingly solid investment. And the more cautious grillers among us might want to let the reading climb past 160 degrees. The UAlberta researchers believe that government agencies will want to take a look at their research.
“If [LHR] is in two percent of all E. coli, and in pathogenic E. coli, there’s the potential that a pathogen could survive the standard cooking protocols for ground beef,” McMullen warned in the UAlberta’s report. “It could mean we have to change the guidelines for cooking meat, because 71 degrees Celsius [160 degrees Fahrenheit] may not be enough.”
The most notorious burger-related E. coli outbreak in the United States occurred in 1993, when hundreds fell ill after eating at the fast food chain Jack in the Box. But the CDC has recorded smaller E. coli outbreaks tied to ground beef as recently as 2014. In that latest outbreak, 11 of 12 people who got sick recalled having eaten a burger that was cooked medium rare or below.
As the CDC notes, E. coli infection can cause bloody diarrhea and stomach pain. For small children and the elderly especially, it poses a risk of more serious illness, including kidney damage. That’s a good reason to play it safe at your next family barbecue.