E. coli in your spinach: an unsolved mystery

The human stomach has a natural barrier that kills food-borne bacteria - the highly acid (pH2) stomach juices. These juices normally keep us from harm unless we eat so many bacteria at one time that some slip through the stomach alive (think about that picnic potato salad that sat unrefrigerated for hours), or if we ingest a pathogen that has evolved to overcome the protective barrier of the stomach. E. coli O157:H7 is in the latter category.

This E. coli strain is so highly toxic that only a few of these microbes can cause eight days of severe cramping and abdominal pain, diarrhea, vomiting or low-grade fever, and even kidney failure. More than half of those infected in the current outbreak (CDC reports 166 in 25 states, five cases in Arizona, as of Friday) were hospitalized and one adult has died of kidney failure due to hemolytic uremic syndrome.

Investigations point to fresh spinach as the reservoir of the current outbreak. Suppliers and grocery stores are pulling fresh spinach off the shelves. The lead shipper indicated in the outbreak is Natural Selection Foods. They package salad greens for two dozen brands and stepped up to initiate the spinach recall. The source of the contamination has been traced to three counties in California. Millions of dollars are at stake. So far, there is no evidence that the spinach was mishandled at any point in the distribution chain. Irrigation water is suspect, though no particular infection has been traced to a river or other water supply.

The CDC and the FDA have deployed investigators to California to look into possible environmental sources of the outbreak. We have a mystery on our hands.

What is the source of the toxic E. coli? We are used to E. coli O157:H7 outbreaks from contaminated uncooked beef, and have learned that it is not a good idea for a restaurant worker to slice watermelon with the same knife used to cut raw beef nor is it a good idea to eat rare hamburger. But raw spinach, even washed raw spinach? Reports say that the bacteria may be inside the leaf, so washing will not help. Clue: If that is true, then the spinach must have been contaminated as it grew in the field. Clean out your refrigerator, throw away the bag of fresh spinach - the kids will be happy about that!

So why is the water supply suspect? Today's cattle are grain-fed because the grain increases the rate of growth and produces tender meat. We have become accustomed to tender steaks. This process began in earnest around 40 years ago and has since grown into huge feedlot businesses. Store-bought meat from range- or pasture-fed cattle is rare these days. The cow digestive tract (I'll try to be sensitive here) does not digest starchy foods well, so there is still undigested food that reaches the lower end of the tract. While this undigested food is in a holding pattern before elimination, it ferments and produces various acids - acetic, proprionic, and butyric acids. As more acid is produced, the lower digestive tract becomes more acidic. Today's grain-fed cow has a harder time digesting grain than its ancestors did digesting grass or hay. Less digestion, more acid, lower pH. This is a new environment for intestinal bacteria.

The very toxic E. coli O157:H7 has evolved from common E. coli to live in this highly acid environment where the acidity is similar to that of the human stomach. It has evolved to live in this acid niche from 40 years in the gut of feedlot cattle. Your stomach acid does not protect you from this invader.

We thought we had this problem solved - feed the beef cattle hay for five days before they're sent to market and the toxic E. coli are left in the feedlot. Contain the runoff from the feedlot in reservoirs so that groundwater is not contaminated. Feedlots are under weighty government restrictions to contain animal waste. With these restrictions, our groundwater and rivers should be safe from E. coli O157:H7 contamination. Are we just now finding out that it is not? Grain-fed cattle must be the first source of the contamination, but where has the system broken down? How did it get into bags of fresh spinach? And why not lettuce and other produce?

Any ideas? This is much more than a game of Clue. This is real-life problem-solving that we should all take an interest in. This problem demonstrates that our food chain is vulnerable at every link.

In the meantime, be aware of the hazards of E. coli O157:H7 and clean out your refrigerator. Do not open the bag of spinach and touch it. Throw it out! The CDC says the incubation period is 3-4 days, so if you threw out your fresh spinach last week, you should be out of danger.