Way to go, all you planet-saving shoppers who’ve made the switch to reusable bags! But consider: “Reusable” doesn’t mean “self-cleaning.”

Researchers at the University of Arizona and Loma Linda University queried shoppers headed into grocery stores in California and Arizona, asking them if they wash those reusable bags. The researchers were likely met with a lot of blank looks. Most shoppers — 97 percent, in fact — reported that they do not regularly, if ever, wash the bags.

Further, three-fourths acknowledged that they don’t use separate bags for meats and for vegetables, and about a third said they used the bags for, well, all sorts of things (storing snacks, toting books). You can see where this is going.

The researchers tested 84 of the bags for bacteria. They found whopping amounts in all but one bag, and coliform bacteria (suggesting raw-meat or uncooked-food contamination) in half. And yes, the much-feared E. coli was among them — in 12 percent of the bags.

The researchers wrote in their discussion of the findings:

“It is estimated that there are about 76,000,000 cases of food-borne illness in the United States every year. Most of these illnesses originate in the home from improper cooking or handling of foods. Reusable bags, if not properly washed between uses, create the potential for cross-contamination of foods.”

The study, funded by the American Chemistry Council, also assessed the effectiveness of washing the bags. Machine washing or hand washing reduced bacteria levels to almost nothing.