Many communities in southern California have banned plastic grocery bags and required surcharges for paper bags in hopes of convincing shoppers to switch to reusable bags.

But now a study shows that reusable grocery bags may pose a health risk.

Reusable bags tested positive for E. coli, salmonella and coliform bacteria, according to studies by Loma Linda University and the University of Arizona.

The bacteria proliferated wildly when the bag was left in a hot car.

A whole haul of groceries could be infected by contaminated bags, said health educator Rosemary Anthony.