When Cooking Doesn’t Kill (Super heat-resistant E. coli)

E. coli (https://www.newfoodmagazine.com/news/63687/e-coli-outbreak-us-canada-linked-lettuce/)

Today was Day 2 of the conference, but really Day 1 of the presentations and such. I presented a poster on my research on outbreak-associated Salmonella, which largely involved standing around bored for twenty minutes, then talking to someone for five, then having three people at once, then being bored for ten minutes, and repeat. But I had a lot of good conversations about science and met a bunch of scientists doing really interesting things or research similar to mine.

In between presenting my poster presentation during the two poster times, I attended a series of talks on heat-resistant E. coli. Normally, E. coli dies off quite quickly when heated above 98.6F (160F is the USDA recommended cooking temperature for ground beef). However, three different research groups in Canada and Europe have found E. coli which is quite happy to survive at temperatures above 140F, and some which aren’t killed down to safe levels until heated past 163F-165F. They found this in water from water treatment plants, in beef processing facilities, and (if I recall correctly) in dairy plants.

So what’s going on? It turns out there’s a chunk of genes (think of a gene as a computer program) called the LHR which can be spread from one bacterium to the other which provide most of these bacteria’s super heat resistance. If you give heat sensitive E. coli the LHR, they become heat resistant. If you delete the LHR from a heat-resistant strain, it becomes heat sensitive. Unfortunately, this chunk of genes also helps the bacteria form biofilms (super stress resistant slime-covered communities) better, too, and also gives them some resistance to chlorine. A bunch of the E. coli with the LHR also have a lot of antibiotic resistance genes, too. So the LHR is bad news all around if you’re trying to kill off E. coli.

Now for the good news: very few pathogenic (dangerous to humans) E. coli have the LHR–the researchers today said it’s around 2% of the pathogenic E. coli they’ve tested. Mostly, the E. coli picking up the LHR are relatively harmless to humans (so not like the O157:H7 E. coli which caused the giant Romaine outbreak earlier this year).

So it’s not a problem? Unfortunately, that’s not quite true, either. Because genes can be swapped around between bacteria, there’s always the possibility the super stress-resistant LHR-carrying E. coli will pick up the genes needed to be pathogenic or that pathogenic E. coli will pick up the LHR. So it’s important to keep an eye on these bacteria. To paraphrase the famous quote, the price of freedom from stress-resistant, virulent superbugs is eternal vigilance.

Signing off to attend the annual extended lab family reunion (my PhD advisor’s students and their students and their students–you get the picture)

References:

Heat Resistant E. coli–some like it hot (Short symposium) IAFP 2018

Lynn McMullen, University of Alberta (Canada). Heat Resistant Enteric Bacteria from Food Processing Facilities: a cause for concern?

Joerg Hummerjohan, Agroscope, Food Microbial Systems (Switzerland). Transferable Heat Resistance in Food and Clinical E. coli Isolates

Norman Neumann, University of Alberta (Canada). Extremely Heat-Resistant E. coli in the Food-Water Nexus.

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