Bacteria in the fridge: a health threat
Bacteria in indoor environments, where we live and eat, are potentially dangerous elements for public health. Various species of microbial populations live in kitchens, and refrigerators, the primary food storage place in kitchens, can be a direct source of illness. Therefore, monitoring different types of bacteria in the refrigerator is important for food safety. Proteobacteria, Firmicutes, Actinobacteria, and Bacteroidetes are common bacteria in the refrigerator and the toilet. Although not all pathogens pose a risk, it is necessary to attach particular importance to sanitizing and disinfecting spaces to avoid health problems.
Contents
- What are the most contaminated places in the kitchen?
- What are the most common bacteria found in a kitchen?
- Case study
- Bacteria and high-touch surfaces
- Creating and maintaining a proper cleaning routine throughout the house
1. What are the most contaminated places in the home?
Microbes inside our homes have been frequently studied in the context of human health using culture-dependent and culture-independent techniques. Most studies (Source, Source, Source) have focused on bacterial contamination of surfaces in kitchens and toilets, microorganisms that are easy for microbes to colonize. Some pathogenic bacteria can survive on surfaces in these environments for a period of time, and food contamination by these pathogenic bacteria can cause illness.
Because refrigerators are used to store food, the humidity and nutrients (food particles) in refrigerators provide favorable growth conditions for bacteria contaminating unwashed raw foods, as well as on leaking packaging and on hands. In particular, a higher number of bacteria and higher temperatures in vegetable drawers could cause critical issues (Source). Furthermore, unwashed vegetables could be a risk element in the entire process of bacteria propagation.
Identifying sources of bacterial contamination is important for food safety management. Human skin is a primary source of bacteria, and humans can transmit bacterial pathogens by touching indoor spaces.
2. What are the most common bacteria found in a kitchen?
The main types of bacteria found in food are salmonella, E. coli, shigella, Bacillus cereus, listeria, and campylobacter. These bacteria are more likely to affect children, older adults, and people with compromised immune systems.
Salmonella, shigella, campylobacter, and pathogenic E. coli are bacteria found in raw meat, contaminated produce, and other contaminated food and water. They produce toxins that can cause intestinal illness, the main sign being watery diarrhea. (Source)
On the other hand, among the most common types of bacteria found on hard surfaces in the home, especially in the refrigerator, is proteobacteria. These household bacterial communities have been compared to those of human skin and intestines to identify potential sources of household bacteria.
Bacterial communities in refrigerators and toilets have more species in common with human skin than with intestines. Opportunistic pathogens, including Propionibacterium acnes, Bacteroides vulgatus, and Staphylococcus epidermidis, have been identified as species shared with the human skin and gut microbiota. (Source)
Although it is true that we cannot find a surface without bacteria on it, most of the bacteria we come into contact with day to day are common, harmless species. Of the bacteria found in indoor air, the four most common are: Micrococcus, Staphylococcus, Bacillus, and Pseudomonas.
Micrococcus is a sphere-shaped bacterium (coccus/cocci generally means spherical), relatively harmless. It is very common on the skin and can also be found in soil, water, and meat products. In general, it is a saprophyte (meaning it feeds on dead and decaying material) and can cause fish spoilage.
This organism can also be responsible for producing the unpleasant odor of human sweat. In immunocompromised people, it can be an opportunistic pathogen. Some common species include M. luteus, M. roseus, and M. varians. Micrococcus needs oxygen to grow and reproduce.
Staphylococcus is another sphere-shaped bacterium. It is much better known than Micrococcus, especially in the context of hospitals, referring to a particularly drug-resistant strain of this bacterium.
3. Case study
A study (Source) conducted by the NSF International Household Germ Study suggests that prevention starts with keeping the kitchen clean. Scientists analyzed common kitchen surfaces and appliances and found an assortment of bacteria, including major causes of foodborne illness, including E. coli, salmonella, and listeria monocytogenes.
The NSF asked 20 volunteer families to swab 14 common kitchen items: blender, can opener, cutlery storage tray, food storage containers with rubber gaskets, knife block, microwave keypad, pizza cutter, spatula, colander, and refrigerator ice dispenser, water dispenser, and meat and vegetable compartments.
The analysis focused on four types of bacteria linked to foodborne illness: E. coli, salmonella, yeast and mold, and listeria.
The presence of these elements in the kitchen is considered a health risk, especially for those most susceptible to foodborne illnesses, including pregnant women, older adults, and people with weakened immune systems.
Study results
Twenty-five percent of tested items contained E. coli bacteria, including the refrigerator meat compartment, rubber spatula, blender gasket, can opener, and pizza cutter. Bacteria E. coli can spread through contaminated food and water, causing diarrhea, urinary tract infections, pneumonia, and other complications that can affect blood cells and kidneys.
Salmonella was found on 25% of tested items, including refrigerator meat and vegetable compartments, spatula, blender, gasket, refrigerator ice and water dispensers, and rubber gaskets of food storage containers. Salmonella bacteria can cause the infection salmonellosis, a disease that can cause diarrhea, fever, stomach cramps, or more severe complications in at-risk groups, including the elderly, the very young, and people with weakened immune systems.
Yeast and mold were found on 100% of all 14 items. Six items had particularly worrying levels of mold, including the refrigerator vegetable compartment, spatula, blender gasket, refrigerator ice and water dispensers, and the rubber gasket on a food storage container. These contaminants can enter food and accelerate spoilage or lead to allergies for some people.
Listeria was found on 10 percent of all tested items, including the refrigerator vegetable compartment and the refrigerator door gasket. Bacteria Listeria monocytogenes can cause fever, muscle aches, and gastrointestinal symptoms.
In no particular order, the six most contaminated items in the kitchen were determined to be the refrigerator vegetable and meat compartments, blender gasket, can opener, rubber spatula, and the rubber-sealed food storage container. These items come into direct contact with food, especially raw produce, meat, and ready-to-eat meals. (Source)
4. Bacteria and high-touch surfaces
There are certain surfaces in the home that we are much more likely to touch than others. We wash our hands several times a day and put the kettle on for hot drinks, so both the kettle and the kitchen faucet have high-touch status.
Likewise for door handles, as they provide us with the only way to enter and exit a room. Other areas near door handles can also be a frequent touch point. Perhaps even more than the toilet lid.
Everyone knows it is important to clean the toilet, perhaps because we associate a higher risk of illness from it if we do not maintain a high level of cleanliness. However, we may be more relaxed about other areas of the house. Kitchen faucets are wiped several times a day, yes… but how often do we do this with a soapy cloth that we then reuse in many other places?
Kitchen items that are most often contaminated include:
- Can openers
- Cutting boards
- Countertops. Most people use kitchen countertops not only for food preparation but also for potentially contaminated items such as shopping bags, mail, or household items.
- Dishes, towels, sponges, and brushes
- Trash can lid
- Kitchen sink drains and faucets
- Refrigerators
- Appliances, such as food processors, blenders, and others.
5. Creating and maintaining a proper cleaning routine throughout the house
Regularly disinfecting touch points throughout the house has become something many of us have done much more since the start of 2020 and the coronavirus pandemic. With house keys topping the list of items we rarely—or even never—clean, followed by car keys, it is clear that we could all stay a little safer if we focused on improving the cleaning and disinfection tasks that can eliminate bacteria.
A kitchen can look perfectly clean. But it can be contaminated with plenty of disease-causing organisms. Cleaning and disinfecting are 2 different things. Cleaning removes grease, food residue, and dirt, as well as a large number of bacteria. But cleaning can also spread other bacteria around. Disinfecting kills organisms (bacteria, viruses, and parasites).
Klintensiv Tip: To streamline the process of removing bacteria, we recommend using dual-action cleaning and disinfecting products. KlinAll® degreaser disinfectant is an extremely useful product for disinfecting surfaces and cleaning grease stains, burnt-on food, and oil stains on surfaces in kitchens and cooking spaces.
Disinfectants are widely available in the form of liquids, sprays, or wipes. Any of these work well, killing almost all bacteria and viruses.
An extremely important aspect is that disinfection is only done after surfaces have been deeply cleaned of organic matter. Food or grease deposits will not allow the disinfectant to act.
The way dishes and utensils are dried also plays an important role in kitchen hygiene. From least to most effective, drying processes can be ranked:
- Towel drying (least effective)
- Paper towel drying
- Air drying
- Dishwasher drying
- Sterilization cycle in the dishwasher, if available (most effective)
Not all microorganisms are the same, and some are much more resistant than others. Viruses are responsible for most common household illnesses. Most viruses, including those that cause the common cold, are only able to live on dry surfaces in the environment for a few hours. Bacteria, on the other hand, tend to be more unwelcome guests in the home and, under the right conditions, can live for months!
Conclusion
Refrigerators can be spaces conducive to the development of bacterial colonies, and these bacteria could contaminate other stored food or attach and survive on the interior surface of the refrigerator, thus posing risks of indirect contamination. This potential risk can be prevented by wrapping stored food and regularly cleaning kitchens, including refrigerators. Using cleaning and disinfecting products, along with rigorous hand hygiene, are effective solutions for preventing a large number of health problems.
Sources:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3790245/
https://www.moldbacteria.com/bacteria/what-bacteria-are-really-in-indoor-environments.html
https://intermountainhealthcare.org/blogs/germiest-places-in-your-home-might-surprise-you
https://d2evkimvhatqav.cloudfront.net/documents/2011_NSF_Household_Germ_Study_exec-summary.pdf
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3223236/
