E.coli bacteria from a domestic fridge. Animated coloured scanning electron micrograph of rod-shaped Escherichia coli bacteria found in a domestic fridge. Tests on samples from the salad drawers of 30 frost-free home fridges showed they had an average of 7, 850 bacteria colony-forming units per square centimetre. The standard EC recommendation for 'clean' food preparation and storage surfaces is for 0-10 cfu cm2. Potentially harmful bacteria such as E. coli, Salmonella and Listeria were among those found. Some of these are psychrophilic bacteria that have the ability to divide and multiply in cold temperatures.