Information – Will Washing Romaine Lettuce Remove E. coli O157:H7?

Food Poisoning Bulletin 

Consumers are asking questions about this outbreak; namely, how can they protect themselves and their families? One of the questions is: will washing romaine lettuce and other produce eliminate the pathogenic bacteria?

The answer is, unfortunately, no. There are several reasons for this.

First, it only takes 10 Shiga toxin-producing E. coli bacteria to make a person very sick. That tiny amount is invisible to the eye. Washing romaine lettuce will not remove all the bacteria from microscopic surface of every leaf. Experts say that washing romaine lettuce and other produce can only reduce the number of bacteria that may be present, not completely eliminate them.

Second, pathogenic bacteria such as E. coli O157:H7 can form biofilms. These bacteria tend to cluster in small clumps so they can communicate with each other and protect each other. The bacteria produce a matrix made up of proteins, polysaccharides, and nucleic acids. The matrix is very dense and protects the bacteria from cleaning agents. It also protects the bacteria from antibiotics, and even desiccation. A simple rinse with water or a cleaning solution may not penetrate that biofilm.

And finally, the deeply crenelated surface of leafy greens provides lots of places for bacteria to hide. The same is true for other types of produce, especially cantaloupe. And, if there are tiny tears, bruises, or rips in the lettuce leaf, the bacteria can actually get inside. No amount of washing any kind of produce can reach the bacteria then.

The only thing that will kill E. coli bacteria is heat; the food must be heated to 160°F. There are very few recipes that call for cooked romaine lettuce. Grilling romaine lettuce halves will not increase the temperature enough to kill any bacteria that may be present.

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