Where microbes accumulate in the kitchen

Along with the bathroom, it is the most polluted environment in the home, but there is a very popular utensil that is the main focus of pathogens

Kitchens, along with bathrooms, are often the most polluted domestic environments. It is common to isolate pathogens from countertops, utensils, complex appliances such as kitchen processors and blenders, can openers, sink drains, washcloths, cutting boards, sponges and scouring pads.

In particular, wooden utensils — whether spoons, forks, cutting boards, or some other cloth — which are highly valued and used in the domestic environment, are prohibited in the catering sector, as they are not considered safe enough on a microbiological level. What's more, as early as 1991 the US Department of Agriculture published a recommendation that students who go to college and cook for the first time should not use wooden cutting boards either.

The reason, in both cases, is that wood is a porous material that preserves moisture, necessary for microbial growth. To top it off, it tends to deteriorate, forming cracks in which countless microorganisms can be housed. For this reason, it is advisable to use articles made of plastic, metal or silicone. Also at the domestic level.

However, the debate is not without controversy. Because there are also studies that suggest that the rough surface of wood is hostile to bacteria. Even some analyzes indicate that wood has antibacterial properties.

Kitchens as a source of infection

Although consumers' perception of the risk of contracting foodborne diseases in the home environment is very low, the fact is that cross-contamination in household kitchens represents a major domestic source of infection. In 2014, 37.3% of food-borne outbreaks in the European Union germinated in domestic environments. Similarly, according to one of the latest surveillance reports from the US Center for Disease Control (CDC), in 2016 there were 76 outbreaks (10%) and 895 cases of illness (7%) in that country that were attributed to food prepared in private homes.

In recent years, European Union reports indicate that several foodborne diseases are linked to domestic sources of infection. Improper handling of food, not washing hands before preparing food and handling food and unhygienic practices are considered the main factors in foodborne illness episodes.

The list is extensive, but the bacterial genera Salmonella, Campylobacter, Listeria and Brucella, the bacteria Escherichia coli verocytotoxigenic (VTEC), noroviruses, hepatitis A virus and parasites such as Taenia solium, Echinococcus, Ascaris, Cryptosporidium, Entamoeba histolytica or Giardia tops the list of common foodborne pathogens that affect millions of people every year.

Scouring pads or kitchen sponges, the main source of pollution

Among the potential microbiological foci in domestic environments, kitchen sponges or scouring pads stand out. They are often used not only for cleaning dishes and kitchen utensils, but also different surfaces or even refrigerator shelves, which increases the risk of cross-contamination.

Thanks to the large surface/volume ratio of the sponges, the usual constant moisture they present, the porous and airy structure and the nutrients for bacterial growth they contain (from food debris), they are an ideal habitat for microorganisms. It is estimated that they are capable of harboring 54 billion bacteria per cubic centimeter.

Several studies on the microbiological quality of scouring pads warn that they usually contain a high level of contamination and that the isolation of pathogens such as Salmonella spp., Acinetobacter spp., Moraxella spp., Staphylococcus aureus, Campylobacter spp., Listeria monocytogenes, Enterobacter cloacae, Klebsiella oxytoca or Cronobacter sakazakii. An analysis conducted in 1997 in 10 kitchens in the US found that 33% of the sponges tested were positive for Escherichia coli and 67% for fecal coliforms.

A study conducted in 2020 on the microbiological quality of kitchen sponges used in university residences.) revealed that students used them to wash items such as cutlery, plates and glasses, but also to clean the oven (32%), the sink (26%), the refrigerator (10%) and even spills on the floor (4 %).

The analyses showed that the sponges used contained high counts of mesophilic aerobic bacteria (79 billion bacteria per cubic centimeter), coliforms (72 billion bacteria per cubic centimeter), enterobacteria (73 billion bacteria per cubic centimeter), and yeasts and filamentous fungi (70 billion bacteria per cubic centimeter). cells per cubic centimeter). The most frequently isolated enterobacteria were Enterobacter cloacae (56%) and Klebsiella oxytoca (16%), both human pathogens. All Enterobacter cloacae isolates were resistant to antibiotics such as amoxicillin, cephalotin, cefoxitin and cefuroxime-axetil.

In short, there is no doubt that, due to the account that it brings us, it is advisable to regularly renew our sponges.

*Raúl Rivas González, is Professor of Microbiology, University of Salamanca

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