Knives and graters spread bacteria

Bacteria can be spread from contaminated produce to other foodstuffs via common kitchen utensils such as knives and graters, a study has found.

In a study funded by the US Food and Drug Administration, University of Georgia researchers found that bacteria would latch on to the utensils and spread to the next item.

Many consumers are unaware that utensils and other surfaces at home can contribute to the spread of bacteria, said the study’s lead author, Marilyn Erickson, an associate professor in the College of Agricultural and Environmental Sciences’ department of food science and technology.

“Just knowing that utensils may lead to cross-contamination is important,” Erickson said. “With that knowledge, consumers are then more likely to make sure they wash them in between uses.”

The study, published in Food Microbiology, considers what standard kitchen practices are more likely to lead to contamination.

Erickson contaminated many types of fruits and vegetables in her lab — adding certain pathogens that often can be found on these foods, such as Salmonella and E. coli.

Using a knife, she would cut into produce such as tomatoes or rockmelon to see how easily the bacteria could spread when the knife was continuously used without being cleaned.

Researchers also grated produce, like carrots, to see how easily the pathogens spread to graters. They found that both knives and graters can cause additional cross-contamination in the kitchen and that the pathogens were spread from produce to produce if they hadn’t washed the utensils.

“A lot of the broken up material and particles from the contaminated produce remained on the graters,’ said Erickson. “Then if you were to shred another carrot or something else immediately after that, it gets contaminated, too.”

The study also found that certain fruits and vegetables spread pathogens to knives to different degrees.

“For items like tomatoes, we tended to have a higher contamination of the knives than when we cut strawberries,” Erickson said. “We don’t have a specific answer as to why there are differences between the different produce groups. But we do know that once a pathogen gets on the food, it’s difficult to remove.”

Knives and graters aren’t the only utensils in the kitchen consumers should be worried about. Erickson has also helped study the role brushes and peelers have on the transfer of dangerous kitchen bacteria.

In concurrent studies, Erickson found that scrubbing or peeling produce items — like melons, carrots and celery — did not eliminate contamination on the produce item but led to contamination of the brush or peeler. Even when placed under running water, the utensils still became contaminated; however, the ability to cross-contaminate later produce items depended on the brush type and the pathogenic agent.

These studies combined give researchers a better idea as to how common cross-contamination is in the kitchen — even when just using standard practices.

Erickson explained there is a small chance of buying fruits and vegetables contaminated with bacteria, but the problem can occur whether the product is store bought or locally grown.

Image caption: Associate Professor Marilyn Erickson grates a carrot to test the chances of cross-contamination in home kitchens. (Credit: Sharon Dowdy/UGA)