If you're curious where most of the bacteria lurks in your house, wonder no longer. Kitchen sponges are now the undisputed leaders of bacteria stockpiling.
The research, published in Scientific Reports, looked at the microbial diversity of building environments. Unsurprisingly, they found that a kitchen sponge is a good place for bacteria – after all, it tends to remain rich in water and come into contact with food – but most of us don't know just how much bacteria. Sponges show a local density of 54 billion bacterial cells per cubic centimeter. That is equivalent to the number of bacteria estimated to be in human feces.
“Despite common misconception, it was demonstrated that kitchen environments host more microbes than toilets,” the researchers wrote in the 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”
Not only are sponges full of bacteria, they also spread bacteria all around the kitchen when we clean with them. While this might seem utterly disgusting, it’s important to realize that bacteria are everywhere. We have just as many bacterial cells in our body as we have human cells, for example. The focus needs to be on how many dangerous bacteria the sponges harbor.
For this reason, the team produced the first comprehensive analysis of the bacterial microbiome of sponges. They discovered that the most abundant type of bacteria belongs to the Moraxellaceae family, averaging 36 percent across the sample. Moraxellaceae represents the typical human skin bacteria, so we bring them to the sponge, where they multiply and can become potentially dangerous. Most of the bacteria they found was not dangerous, although some were.
"What surprised us was that five of the ten [types] which we most commonly found, belong to the so-called risk group 2 (RG2)," said lead researcher, microbiologist Markus Egert in a statement, "which means they are potential pathogens."
The main three were Acinetobacter johnsonii, Moraxella osloensis, and Chryseobacterium hominis.
The study also looked at how to avoid an overbundance of this bacteria. “Sanitation by boiling or microwave treatment has been shown to significantly reduce the bacterial load of kitchen sponges and can, therefore, be regarded as a reasonable hygiene measure. However, our data showed that regularly sanitized sponges (as indicated by their users) did not contain less bacteria than uncleaned ones.”
The cleaning procedures actually changed the microbiome – and not exactly for the better. Moraxellaceae and Chryseobacterium hominis appeared to increase in number, as they are more resistant than competing bacteria. This suggests that prolonged sanitation of kitchen sponges might have counterproductive effects. The researchers think that to reduce risk, the best option is to replace the sponges regularly.