Your kitchen is not as clean as you think - and the average one hosts more microbes than a toilet, researchers have found.
They say the worst culprit is the kitchen sponge, with one of the samples containing a staggering 54 billion bacterial cells in a 1cm square area.
After analyzing DNA samples from 14 different sponges, researchers discovered they were dominated by a class of bacteria called Gammaproteobacteria - which include a number of human pathogens including bacteria that cause typhoid fever, the plague, cholera and food poisoning.
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The researchers used a method called fluorescence in situ hybridization - which uses fluorescent probes that bind to specific parts of DNA - coupled with confocal laser scanning microscopy, to visualize the bacteria (red spheres) within used sponges (cyan). The black scale bar represents 20 micrometers
After analyzing DNA samples from 14 different used kitchen sponges, researchers based in Germany discovered the dominance of a class of bacteria called Gammaproteobacteria - which include a number of human pathogens including bacteria that cause typhoid fever, the plague, cholera and food poisoning.
Pathogenic, illness-causing bacteria, however, only made up a small amount of the bacteria in the sponge.
But the researchers found that sponge sanitation methods, such as microwaving and boiling sponges, might increase the shares of 'risk group 2 bacteria'.
Risk group 2 bacteria are agents that are associated with human disease which is rarely serious and for which preventative or therapeutic treatments are often available.
The study, conducted by researchers based in Germany, found that kitchen sponges have 'the capability to collect and spread bacteria with a probable pathogenic potential.'
Kitchen sponges, due to their porous nature and water-soaking capacity, represent ideal incubators for microorganisms, the researchers wrote.
The researchers discovered that a sugar-cube sized piece of bacteria in the most bacteria dense part of the sponge contained 54 billion bacterial cells.
For perspective, the human body is made of 37.2 trillion cells, according to the Smithsonian Magazine.
'Despite common misconception, it was demonstrated that kitchen environments host more microbes than toilets,' the researchers wrote in their study.
'This was mainly due to the contribution of kitchen sponges, which were proven to represent the biggest reservoirs of active bacteria in the whole house.'
The researchers also said that 'kitchen sponges not only act as a 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 if food-borne disease