A bacteria bed is a layer of sand which is used to clean air or water from bacteria and other microorganisms. It is actually a type of filter. our beds are a hotbed for bacteria. The study, which had volunteers swab their unwashed sheets over a period of four weeks, found pillowcases contained 39 times more bacteria than pet food bowls at the end of the testing period. And pillowcases that went unwashed for only one week accumulated 17,442 times more bacteria than a toilet seat!