We tend to think that the kitchen is one of the cleanest places in our house. There we handle and cook food, and a good level of hygiene is essential to avoid possible contamination and food poisoning.
However, far from being the aseptic laboratory with a high level of biosafety that we would like, the kitchen is the habitat of a multitude of organisms.
It is common for the edges of countertops, sinks or the ceramic hob in our kitchens to be sealed with silicone. In principle, modern silicones contain certain ingredients in their composition that prevent the development of fungi. But over time they succumb to colonization.
Fungi are favored by the humidity and darkness of the nooks and crannies of the kitchen, and the remains of food that are deposited in them are the perfect food for them.
Most of the fungi in the kitchen have their origin in three sources. In the first place, the fungi that we carry on our skin or on our mucous membranes and that end up deposited on the surfaces that we touch; examples of this are commensal fungi of humans, such as the genus Malassezia , or, surprisingly, the rye ergot fungus ( Claviceps purpurea ). Second, sewage pipes are often colonized by fungi with a greater preference for damp and warm surroundings. These fungi ascend to the drain of the sink -and the sink and the shower too- and release their spores from there; among them are genera such as Exophiala , Fusarium or the pathogenic Candida , sometimes also present on the hands.
But the most usual thing is that the fungi arrive from the air . Countless spores that drift in the atmosphere, and when deposited in a favorable environment, they germinate and develop. They are most common in silicone gaskets and furniture crevices, and include genera such as Cladosporium, Cryptococcus, or Aspergillus , or fungi that colonize food, such as Penicilium or Rhizobium .
In addition to fungi, various types of insects can visit and inhabit our kitchens, especially if we do not maintain scrupulous hygiene standards.
One of the most common groups are ants; capable of entering a kitchen through the edges of doors and windows, cracks in the walls or even, on occasion, digging their nests in the concrete.
Another frequent customer in the kitchen is the group of flies. The most common species is the well – known fruit fly ( Drosophila melanogaster ) . It lays its eggs, of an almost imperceptible size, in ripe fruit, bread or in any food to which it has access. The larvae hatch, feed on the decomposing product, and within a few days, new flies emerge. It is not uncommon to find them in the fruit bowl, in a piece of fruit forgotten for a couple of weeks or in the organic waste bin when it has been stored for a while.
Fruit fly eggs don’t always come from a fly that flies in through a window. Sometimes fresh fruit and vegetables, especially if they have not been washed or treated, have the eggs attached to the skin, and it is only a matter of time before the larvae proliferate.
In addition to fly eggs, there is a large number of bacteria associated with food, which are also part of that ecosystem that is a kitchen. It happens above all if some link in the long and complex food supply chain does not pay enough attention to food safety – and this is relevant at each and every one of the points of the chain, from the farmer to the final consumer. .
It is very common for these bacteria to form biofilms in drains, scouring pads and cleaning cloths , all of which are moist environments that receive and retain food debris.
The most common bacteria are Escherichia coli, which caused the “cucumber crisis” in Germany in 2011 —which had nothing to do with Spanish cucumbers, as was accused, but with fenugreek outbreaks from organic farming—; Staphylococcus aureus , which causes frequent mild food poisoning; and Klebsiella pneumoniae , a known opportunistic infectious disease-causing bacterium.
The presence of these bacteria in food rarely comes from safety failures in the production, transportation or sale of food. Normally, its presence is associated with insufficient hygiene measures in the kitchen in terms of washing hands, surfaces or instruments before handling food, the reuse of the same scouring pads and cloths without adequate cleaning and disinfection between uses, and with little concern, in general, for food security in the home.
Adams, R. I. et al. 2013. The Diversity and Distribution of Fungi on Residential Surfaces. PLOS ONE, 8(11), e78866. DOI: 10.1371/journal.pone.0078866
Carstens, C. K. et al. 2022. Evaluation of the kitchen microbiome and food safety behaviors of predominantly low-income families. Frontiers in Microbiology, 13, 987925. DOI: 10.3389/fmicb.2022.987925
Hamada, N. et al. 2010. Comparison of Fungi Found in Bathrooms and Sinks. Biocontrol Science, 15(2), 51-56. DOI: 10.4265/bio.15.51
Phillips, C. 2013. Living without Fruit Flies: Biosecuring Horticulture and its Markets. Environment and Planning A: Economy and Space, 45(7), 1679-1694. DOI: 10.1068/a45274