Prevention of bacterial infection begins with the well warranted assumption that all meat has been contaminated with at least some disease bacteria. It requires measures to ensure that those bacteria are not spread to other foods, and are eliminated from the meats during cooking. Hands, knives, cutting boards, and countertops used to prepare meats should be cleaned with hot soapy water before being used to prepare other foods. E. coli are killed at 155°F/68°C, so ground meats are safest if their center gets at least this hot. Salmonella and other bacteria can multiply at significant rates between 40 and 140°F/5–60°C, so meats should not be left in this range for more than two hours. Buffet dishes should be kept hot, and leftovers promptly refrigerated and reheated at least to 160°F/70°C.