Nuke Your Sponge!

What's the germiest place in your home? No, it's not the rim of the toilet bowl -- it's your kitchen! Scientists from the University of Arizona sampled surfaces from kitchens and bathrooms in the same house and found that even germs spread by fecal contamination, such as E. coli, were far more numerous in the kitchen.

Foodborne infections from food eaten at home are difficult to monitor but are probably far more widespread than commonly believed. The General Accounting Office estimates that as many as 81 million cases of foodborne illness occur each year in the United States -- only thousands of which are ever officially reported.

Most of the germs in the kitchen are concentrated in the sink, its drain, and the sponge. Sponges provide an ideal way to spread disease because of having an easy surface to cling to and a steady supply of nutrients and moisture. If a sponge stays moist, the number of live microbes doesn't decrease for two weeks. Bacteria can even survive for at least two days in a damp sponge drying gradually in the air. On dry surfaces, bacteria survive no more than a few hours, but that might be long enough to infect food on the counter that was just cleaned with a sponge. Bacteria can live quite happily even on stainless steel.

Most of the 75 dishrags and 325 sponges sampled by the researchers harbored large numbers of virulent bacteria, including E. coli, Salmonella, Pseudomonas, and Staphylococcus.

Cutting boards also provide nice homes for bacteria. Plastic boards provide more contamination than wooden ones simply because the wooden ones pull the moisture and bacteria down deeper under the surface as they dry. (Moist wooden ones provide a lot of bacterial contamination from the surface.)

The good news is that kitchen germs can usually be removed by some method of cleansing. Metal surfaces should be scrubbed with detergent and then rinsed with a solution of dilute bleach. Cutting boards can be scrubbed with soap and water, although it may be impossible to remove all the bacteria embedded in the knife scars on plastic boards, and scrubbing will not remove the bacteria under the surface of wooden boards. Plastic boards are best cleaned in the dishwasher using high water temperature.

The microwave oven is a particularly useful method of disinfection. Even a heavily contaminated wooden cutting board emerged bone dry -- and free of live microbes both on and under the surface -- after 10 minutes in the microwave. Wetting the board speeded the killing, suggesting that the microbes probably boiled to death. Sterilizing dry cellulose sponges took a mere 30 seconds, while wet sponges took a full minute. Cotton dishrags required 30 seconds when dry but 3 minutes when wet.

-- Science News, 9/14/96