EXPLAINED Series: germs

Have you ever wondered about what microorganisms you can find in your home? Many people have not realized that their homes are rich in different microorganisms such as bacteria, yeasts and fungi. However, this is not a reason to start panicking as not all of the microorganisms are harmful. In fact, only a small fraction of microorganisms are responsible for disease and illness while the vast majority is either harmless or even beneficial!   

          There are many factors which are associated with the microbial populations and diversity found in our homes. It has been reported that homes with pets have in general more diverse bacterial species while those with reported water leaks have great numbers of fungi (Medical News Today), The surprising fact about those microorganisms was the location they were found. The highest numbers were observed in dishwashing sponges followed by toothbrush holders, pet bowls, kitchen sinks, coffee reservoirs, kitchen countertops, stove knobs, pet toys, and toilet seats (Medical News Today).

          In terms of the species found in homes, common bacterial species which belong to families such as Streptococcus, Staphylococcus Corynebacteria identified and also the most common fungal species found were Epicoccum nigrum, Leptosphaerulina chartarum and Wallemia sebi (Medical News Today). An interesting fact about the identified bacteria was that the vast majority were not pathogenic or opportunistic pathogenic but they are part of the human microbial flora and can be found in human skill as well (Medical News Today). The most common skin associated bacteria belong to Staphylococcus and Streptococcus species (Morelle, 2015).

          In terms of the pathogenic bacteria identified, many were found in the refrigerator. Specifically in the vegetable compartment there were identified Listeria, Salmonela and certain fungal species  while E. coli were found in the refrigerator meat compartment, as well as on rubber spatulas, blender gaskets, can openers, and pizza cutters (Medical News Today). In addition, other bacteria which were identified in homes were Bacteroides and Faecalibacterium which are linked to faeces (Morelle, 2015).

         Fungi also are usually found in our homes. The most common types of fungi present in our homes are molds which thrive in humid areas and are often caused by prolonged condensation (diydata, 2019). Moulds can grow in ceilings, walls, window frames, furniture and other areas within the home and they leave a discolored object with a dusty texture and a stale and musty smell behind (diydata, 2019). The problem with mold is that it can grow within houses, cars, offices and furniture and it is very difficult to be eliminated and to be controlled. In addition, mould can negatively affect human health as they can be highly toxic and can have long-lasting effect on human health depending on the species and the extent of exposure (aerindustries, 2020).

Some individuals are particularly sensitive to mold and they experience allergic reactions upon exposure to moldy environment. The most common symptoms of people with mold sensitivity include: headaches, sore throat, skin irritation, coughing, sneezing and wheezing, watering, dry or sore eyes and chest and nasal congestion (aerindustries, 2020). Regarding the most popular types of mould found in our homes, molds are divided into three main categories known as allergenic molds, pathogenic molds and toxic molds and the majority of them are species of  Aspergillus, Penicillium, Alternaria and Fusarium. In addition, different species of molds develop also different colors such as black, white, yellow, green, orange and brown mold (Ward, 2020). It should be also mentioned that not all molds are pathogenic as there are more than 100,000 different mold species and a lot of them are completely harmless or even beneficial such as Penicillium species which are involved in cheese making and in antibiotic production.  

Parasites also should be included on this list. By definition, a parasite is an organism that lives within or on a host organism and uses resources from its host in order to survive (Brazier, 2018). Although not all parasites are microbes some of them like protozoa are single celled organism and they can result in severe diseases (Brazier, 2018). The most dangerous example of parasite is Plasmodium which is transmitted by mosquito bites and causes malaria (Brazier, 2018). Other types of parasites include worms. Worms can usually infect humans by consuming contaminated food or water. For example, Blastocytosis is a disease which affects the intestines (Brazier, 2018). The blastocystis enters humans through the fecal-oral route and a person can get it by eating food or drink contaminated with human or animal feces where the parasite is present (Brazier, 2018). It should be stressed though again that parasites need a host in order to survive and they are not able to form colonies like bacteria and fungi (Brazier, 2018). By ensuring that food is fully cooked, using insect repellant, and following good hand hygiene rules can reduce the risk of getting parasites (Brazier, 2018).

          Another category of microorganisms are viruses. Viruses however are not regarded by the scientific community as living entities. According to scientists viruses are more like “chemical structures” as they need the replication mechanisms of their hosts in order to replicate. Viruses are responsible for a great range of diseases but as they cannot replicate themselves without a host, they transmitted by infected individuals to healthy ones. Additionally, it has been reported that viruses can survive into different surfaces for days so a proper cleaning of our house and good personal hygiene are required in order to prevent viral spreading.  

          Finally, it should be mentioned that most houses have a great number of dust mites. Dust mites are parasitic organism and are responsible for allergic reactions such as wheezing. Most mites are tiny, less than 1 mm (0.04 in) in length, and have a simple, unsegmented body plan. Certain individuals are very allergic to dust mites and as a result they develop symptoms such as allergic rhinitis and asthma upon

contact with dust mites. However it should be mentioned that most mite species are harmless to humans but a few are associated with allergies or may transmit diseases.

         In conclusion, our houses, offices and cars can contain a great number of different microorganisms. The majority of them are not harmful and they do not cause any disease. However, certain microorganisms can result in severe disease cases and might required medical treatment. A good cleaning, good cooking and good personal hygiene can reduce the possibilities for an infection.


Aerindustries. (2017). 12 common types of mold in homes. Aerindustries (Online) Accessed on 23rd of May 2020 from: https://aerindustries.com/blog/2017/03/28/common-types-mold-in-home/

Brazier, Y. (2018). What to know about parasites. Medical News Today (Online). Accessed on 23rd of May 2020 from: https://www.medicalnewstoday.com/articles/220302

Diydata. (2020). Mould in the house. Diyadata (online). Accessed on 23rd of May 2020 from: https://www.diydata.com/problem/mould-in-the-house/mould-house.php

Medical News Today. (2020). Household microbes: Friend or foe? Medical News Today (Online). Accessed on 23rd of May 2020 from: https://www.medicalnewstoday.com/articles/319750#Microbes-that-might-give-us-the-edge

Morelle, R. (2015). Thousands of microbes found in house dust. BBC (Online). Accessed on 23rd of May 2020 from: https://www.bbc.com/news/science-environment-34056549

Ward, J. (2020). Types of toxic mold that can hurt you. Mold Busters (Online). Accessed on 23rd of May 2020 from: https://www.bustmold.com/resources/about-mold/types-of-mold/

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