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Does Washing Lettuce Get Rid of Bacteria?

2010-05-13 10:32:16

Jeanna Bryner and Karen Rowan

Staff Editors

LiveScience.com Jeanna Bryner And Karen Rowan

staff Editors

livescience.com Wed May 12, 11:30 am ET

As the recall of tainted romaine lettuce expands, many plates could be devoid

of the crisp veggie in an effort to stay healthy. That might be a good idea,

according to experts who say that washing produce, even very carefully, may not

remove all the bacteria present.

At least 19 people became sick last week including three with life-threatening

symptoms, according to the Centers for Disease Control and Prevention (CDC).

An estimated 76 million cases of foodborne disease occur each year in the

United States, according to the CDC, and the bacteria that cause these

illnesses, such as Salmonella or E. coli, can hang on tight to food even

through a washing.

"If you've got bacteria on the surface of fruits and vegetables, and you give

them a wash with cold water, it removes some of what's on the surface," said

Brendan Niemira of the USDA's Microbial Food Safety Unit in Pennsylvania.

"Unfortunately, it [cold water rinsing] doesn't remove all of them, and that's

a problem. If things are well-attached or living in a tight-knit community

called a biofilm, that's going to be hard to get rid of."

Rough surfaces, like those on cantaloupes and spinach, provide lots of nooks

and crannies in which bacteria can hide out, Niemira said. Tomatoes are much

smoother, though their surfaces do contain tiny pores that make homes for

bacteria.

You would want to wash rougher-surfaced fruit more carefully. Niemira cautions,

however, too rough of a cleaning can bruise or tear the protective layer

covering tomatoes and other fruits and vegetables.

"Most bacteria can't be washed off," agreed Doug Powell, associate professor of

food safety at Kansas State University. And although it happens rarely,

bacteria in soil can also be taken up by the roots of plants and remain inside

the plant's veins, where they would be impossible to remove by washing.

For vegetables and other foods that are eaten raw, the best way to prevent

outbreaks like this one involving romaine lettuce is through cleaner farming

practices, Powell said. When the water used to irrigate the food crops is drawn

from wells that are near livestock, fecal bacteria can spread through the water

to the food. And when manure is used to fertilize the soil, bacteria can easily

colonize the plants. Farm workers need to be careful when they handle the

crops, because bacteria on their hands can transfer to the crops, he said.

"We need to make sure that the water is clean, that some soil amendments aren't

used, that the hands and the shipping containers that come in contact with the

crops are clean, and that animals are kept away," Powell said.

Some crops may be more easily contaminated than others. The current outbreak is

believed to be due to contaminated romaine lettuce, and Powell said the way

romaine grows makes it easy for bacteria to take hold.

"New leaves grow up around the other leaves," within a head of romaine lettuce,

Powell said, so bacteria find a sheltered environment between the leaves in

which they can thrive.

Although the disease-causing bacteria are also found in meat, cooking kills the

bacteria.

"Fresh produce is the common source of outbreaks because it's eaten raw,"

Powell said, "And anything that comes into contact with it has the potential to

contaminate it -- think about all of the places that produce goes after it

leaves the farm."