disgusting... I always thought that kitchen sponges could be sanitized! not true == http://www.sciencemag.org/news/2017...-microbes-cleaning-it-could-make-things-worse That sponge in your kitchen sink harbors zillions of microbes, including close relatives of the bacteria that cause pneumonia and meningitis, according to a new study. One of the microbes, Moraxella osloensis, can cause infections in people with a weak immune system and is also known for making laundry stink, possibly explaining your sponge’s funky odor. Researchers made the discovery by sequencing the microbial DNA of 14 used kitchen sponges, they report this month in Scientific Reports. Surprisingly, boiling or microwaving the sponges didn’t kill off these microbes Indeed, sponges that had been regularly sanitized teemed with a higher percentage of bacteria related to pathogens than sponges that had never been cleaned. This could be because pathogen-related bacteria are more resistant to cleaning and rapidly recolonize the areas abandoned by their susceptible brethren—similar to what happens to our gut after an antibiotic treatment, the scientists say. When the researchers put the sponges under the microscope, they discovered that a single cubic centimeter could be packed with more than 5 x 10^10 bacteria, which corresponds to around seven times the number of people inhabiting the Earth. Such bacterial densities, the scientists say, are found only in feces. But don’t worry—the solution to a clean sponge is simple: Just replace it every week. https://www.nature.com/articles/s41598-017-06055-9 In addition, microwave and boiling treatments were shown to significantly reduce the bacterial load. However, results were contradictory, for example showing effectiveness in the laboratory, but not in used kitchen sponges18, and no method alone seemed to be able to achieve a general bacterial reduction of more than about 60%. Kitchen sponges not only act as reservoir of microorganisms, but also as disseminators over domestic surfaces, which can lead to cross–contamination of hands and food, which is considered a main cause of food–borne disease outbreaks.