How much bacteria lives on a bathroom door handle? Every person who touches a restroom door leaves behind microbes. A disinfectant wipe might remove them entirely. You swab the inside and outside handles of restroom doors at six locations. The six locations span three types of venue: - homes - restaurants - supermarkets Each swab gets transferred to a blood agar plate. After 48 hours in an incubator at 35 degrees Celsius, you count the bacterial colonies. Then you wipe each handle with a Clorox disinfectant wipe and swab again. The inside handle carries about 50% more bacteria than the outside. The Clorox wipe reduces the colony count to zero at every location.