Your Regularly Cleaned Kitchen Sponge May Be Dirtier Than You Think

It’s already common sense that kitchen sponges are a reservoir of bacteria.

One solution that has been presented to us over the years is their sanitization, by boiling or even microwaving them, for example. However, according to a recently published study, it was found that regularly sanitized sponges had the same quantity of bacteria as non-sanitized sponges, and also an increased abundance of bacteria related to pathogens. This increase in abundance may be due to the survival of resistant bacteria after sanitation, leaving the sponge free of competition and available to be quickly recolonized.

(A) Kitchen sponges, due to their porous nature (evident under the binocular; (B)) and water-soaking capacity, represent ideal incubators for microorganisms. Scale bar (B): 1 mm. (C) Pie charts showing the taxonomic composition of the bacterial kitchen sponge microbiome, as delivered by pyrosequencing of 16S rRNA gene libraries of 28 sponge samples (top and bottom samples of 14 sponges, respectively). For better readability, only the 20 most abundant orders and families are listed.

The study also emphasizes the presence of a Gram-negative bacterium, Moraxella osloensis, capable of causing infection in immunocompromised people, especially cancer patients, and, curiously, responsible for the characteristic smell of locker-rooms, leading to the hypothesis that “ cleaned sponges might paradoxically smell more often”.
The importance of this study is related to the fact that kitchen sponges act as bacteria disseminators, which in turn “can lead to cross–contamination of hands and food, which is considered a main cause of food–borne disease outbreaks”.

Finally, the solution presented by the scientists is simple – replace kitchen sponges regularly, for example, every week.