In my small, elderly house, the bathroom opens onto the kitchen, which has always worried me: I keep picturing armies of bacteria marching out of the bathroom to contaminate my food.
It turns out my concern is misguided: a recent study indicates it’s more likely bacteria from the kitchen will contaminate my bathroom..
Scientists from the University of Arizona in Tucson tested several houses and discovered the kitchens were almost always more contaminated with bacteria than the bathrooms, even by germs spread by fecal contamination, such as E. coli (source of “Hamburger disease”). In fact, the average toilet rim was relatively germ-free compared to the average counter top.
Bacteria hang around the kitchen for the same reason other unwanted house guests do: that’s where the food is. Preparing food leaves tiny bits of it behind on surfaces, which, unless carefully cleaned, soon teem with bacteria.
It also turns out that swabbing surfaces with that damp sponge you keep in the sink does more harm than good, because sponges and dishrags are often the richest reservoirs of germs in the kitchen. The scientists found that most harbored large numbers of various virulent bacteria that commonly infect animals and people. Twenty percent hosted Staphylococcus aureus; 14 percent hosted salmonella. The bacteria were measured in “colony-forming units”–one or more cells that can produce a colony of bacteria. The scientists found up to 10 million colony-forming units in just one millilitre of liquid wrung from a sponge.
In one house, the researchers found everything in the kitchen heavily contaminated for five days in a row–and then, on the sixth day, the bacteria count dropped to practically nothing. The family had finally started using a new sponge.
Drying a sponge kills bacteria, but it takes a couple of days. Bacteria don’t live long on a dry countertop, either–just a few hours–but that’s plenty of time to infect food.
Moisture also attracts bacteria to sinks. Even apparently smooth stainless steel is full of nooks and crannies on the microscopic level, ideal for bacterial colonization. Bacteria that grow there even produce an organic goo that cements them together, and makes them impervious to fast-flowing water, mild rubbing or even weak detergent solutions.
And then there are cutting boards. A couple of years ago, microbiologist Dean O. Cliver at the University of Wisconsin in Madison found it was easier to recover live bacteria from a plastic cutting board than a wooden one; in the wooden one, the bacteria hid a millimeter or two below the surface. (That only applies to dry wooden boards; you can recover bacteria from a wet wooden cutting board as easily as from a plastic one.)
By this time, you’re probably making plans for a romantic dinner for two in the loo. But sponges, cutting boards, sinks and countertops can be made much safer simply by cleaning them more carefully.
Rubbing the sink or other metal surfaces with strong detergent will dissolve most of the food and microbial material, and a rinse in a dilute bleach solution will wipe out any bacteria that are left. Hand scrubbing can remove most of the microbes from the surface of new or used wooden cutting boards and new plastic ones. (To clean a knife-scarred plastic cutting board, though, you need to put it in a dishwasher.)
Ten minutes on high heat in an 800-watt home microwave oven kills microbes both on the surface and inside a wooden cutting board, although it does nothing to sterilize plastic boards; their surfaces don’t get hot enough. A dry cellulose sponge can be sterilized in the microwave in just 30 seconds; a wet sponge in a minute. Cotton dishrags take just 30 seconds when dry and three minutes when wet.
You should also keep food covered, wash hands thoroughly before handling any food (better yet, use tongs), use separate cutting boards and knives for each type of food, and use paper towels in preference to regular kitchen towels.
You can already buy sponges and cutting boards that kill bacteria on contact; soon you’ll see anti-microbial counter tops, appliances and food packaging, too.
Having suffered through a bout of food poisoning in college, I can assure you that you don’t want to experience it personally, and I don’t want to experience it again. So if you’ll excuse me, I think I’ll go microwave my dishrag.
