Reusable grocery bags
7 Healthcast: Reusable grocery bags
Some are obviously more clean than others, and shoppers differ in the way they care for their reusable bags.
NBC affiliate KXAN asked shoppers to trade their bags for new ones so they could see just how clean their bags really are.
The bags were a mix of large, small, woven natural fabric and manmade.
Some had been used for years and others for just weeks.
KXAN took them to a lab at the University of Texas Molecular Genetics and Microbiology Department where researchers put them under the microscope.
Research assistant Carolyn Fisher took the inside corner of each bag and pressed it against two plates pre-treated with substances to attract the smallest of organisms.
"It would transfer any bacteria on the surface onto the plate," she said.
The clear plates attract any organisms.
The purple plates look for the potentially bad ones, with the bacteria that could make someone sick.
The test plates go into the incubator overnight at 98 degrees, which is the human body temperature, to see what might grow.
Seven of the 10 bags came out pretty clean.
Three of the bags had higher levels of bacterial growth.
Visible were many more clusters of organisms filling the test plates of those three bags.
"You would not expect everything to be completely sterile and have no growth at all, but the level of growth on some of these was high," said University of Texas microbiology professor Shelley Payne.
The high levels of bacterial growth on three of the bags, Payne said, was probably not harmful, but the amount of bacterial growth is a concern.
"Just taking a blot of the inside of the bag, the plate is almost covered with bacteria and fungal growth, and that suggests that there is a considerable amount of contamination," said Payne. "If you had meat in a bag and it leaked -- raw meats are often contaminated with bacteria that can cause disease. If you then had that come into contact with other foods that you didn't expect to have those kinds of organisms, you could transfer the organisms to those and have the potential for disease."
Two samples on the purple plates raised even more questions.
Those plates look for and highlight organisms which could be harmful to the body and are capable of living in the human gut.
They are organisms that could cause food poisoning or worse.
"This is showing us what are called enteric organisms, those that can live in the human gut," said Payne. "Often we will look for enterics as a general clue there is contamination with organisms that could cause food poisoning."
One bag in particular looked the dirtiest.
We saw what looked to be dog hairs inside.
That bag resulted in the most bacterial growth.
"I would not personally want to eat from this bag," said Payne. "The level of contamination is higher than you would like to see. It's going to depend somewhat on how that food is handled after it's taken out of the bag. If it's something washed before it is eaten then it's probably fine.
The test results are dirty little reminders to wash reusable bags often, especially those you take to the grocery store.
"This is one of those things that's just a matter of common sense," said Payne. "You're putting food in a bag, and if you're going to be eating that food, you'd prefer it come out of a clean bag than a dirty one."
The bags KXAN tested that had been cleaned recently had lower levels of bacterial growth.
Most shoppers said they put them in the washing machine.
Health experts advise against using grocery bags for anything other than food.
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