Updated: Aug 26, 2020
If you're living in North America, you've probably already heard about the international outbreak of E. coli linked to romaine lettuce. This week's post is all about this increasingly often phenomenon of food recalls due to E. coli cases. We'll kick it off with a question from my Dad: is it possible to wash lettuce well enough to remove the E. coli off? Is the bacteria in or on the lettuce leaf?
The answer to this question depends on whose perspective you take: the human's, or the E. coli's. From the perspective of the E. coli the bacteria doesn't really get inside of the lettuce plant; the bacteria will coat the surfaces of contaminated leaves. However, you also must remember that E. coli are about 500 times smaller than a ".", and that lettuce leaves will have small rips and tears in it. These blemishes, which are tiny to the human eye, are like the grand canyon to a bacterium, and full of miniscule nooks and crannies just big enough for bacteria to wedge themselves into. It's because of this that it is unlikely that you'd be able to wash off all of the offending E. coli.
Indeed, to protect yourself against the type of E. coli that has been causing these outbreaks, which is from the strain "O157", you'd have to scrub the lettuce rather unrealistically clean – or cook it, but mushy lettuce doesn't exactly tickle my tastebuds, personally. Just like you only need to eat a tiny piece of chili pepper to figuratively set your tongue on fire, you only need to eat a tiny amount of Escherichia coli O157 – just a few individual bacteria – to blow up your intestines. As one of my professors from UBC eloquently put it, the O157 strain of E. coli, unlike the many other harmless or even beneficial E. coli strains which might live peacefully in your gut, causes "WICKED diarrhea".
Luckily for us, most of the time wicked diarrhea is where it ends for human infections, and then we recover. However, E. coli O157 can be deadly to humans if the infection gets out of hand. The bacteria can cause "hemolytic uremic syndrome", a condition in which the bacteria trigger a mass explosion of the human's red blood cells, which then leads to kidney failure.
So how does this bacteria get into our food in the first place? As this paper nicely shows, the main pathway for E. coli O157 to get into human food is via cows and other ruminant (eating-their-own-cud) animals. Cows, for example, can carry this strain in their intestines, meaning that they also poop it out. As a result, anything in contact with cow poop could potentially be contaminated with O157. Although usually farmers and companies are now very careful to test regularly for contamination, it still happens when beef, milk, or vegetables are in contact with cow dung.
So, what is the best way to avoid this contamination, and being infected with E. coli O157? For this one, the answer is not only microbiological, but also has to take into account the way that food is produced today. In particular, there are two big factors that have been making E. coli outbreaks more and more likely to happen.
Firstly, the human population has never eaten so much meat before as a whole. It's easy to forget that when we farm a lot of animals for meat, the side product is, to put it bluntly, a whole lotta crap. Factory farming cows produces mountains of cow poop. And, that poop has gotta go somewhere. Often, "somewhere" is into the water supply, or into fields that will later be used to grow vegetables. Either via the sprinkler water or via the earth itself, this cow poop can then end up on vegetables later sold in your supermarket.
This brings us to our second reason for increased O157 outbreaks. When cows are factory farmed for consumption or milk production, they are not fed their natural diet of grass. Rather, cows are fed grain, which is less expensive and takes up less room. You might remember that, as a human, changing what you eat can change the microbiota in your guts. The same is true for cows. In fact, 20 years ago researchers had already shown that feeding cows grain makes them more likely to carry more dangerous E. coli O157 bacteria in comparison to cattle that were fed grass. More recent studies such as this one and this one have also found that cattle fed grain poop out more E. coli O157 than grass-fed cows, meaning that there is more of the harmful bacteria let out into the environment to possibly infect people.
So, what is the best way to reduce the risk of E. coli O157 infection, then? I would argue that the solution is not washing your vegetables, but rather avoiding eating a lot of grain-fed, factory farmed cattle products. Based on the evidence I can find, the best way to reduce the future risk of O157 outbreaks is to eat less meat overall, and grass-fed meat if any. In the end, we can't really blame the "crappy" vegetables at all, but rather a "crappy" system.
Until next week - cook your lettuce?