The amount of microbes that share our living spaces might come as a surprise to many. But the key question is, are they bad for our health?
When it comes to microorganisms in our living environments, we are bombarded with antibacterial and antiviral soaps, cleaning products of every description, and a general notion that we must keep our houses clean to combat deadly microbial threats.
On the other hand, we are frequently reminded that probiotic microbes have significant health benefits.
Microorganisms are ever-present in our environment and in our bodies, and many are known to be beneficial — or even essential — for our health. However, some are pathogens and can makes us very sick, and they can sometimes even kill us.
Keen to know what microbes might be inhabiting the various parts of my home, I delved into the scientific literature and found out why some of our microscopic roommates are good for us, and why others pose a significant threat to our health.
What microbes lurk around our homes?
Scientists from NSF International — which is based in Ann Arbor, MI — tested 22 households in Southeast Michigan. They found that dishwashing sponges contained the highest number of microorganisms, followed by toothbrush holders, pet bowls, kitchen sinks, coffee reservoirs, kitchen countertops, stove knobs, pet toys, and toilet seats.
In the study, the authors found yeast and molds, bacteria in the coliform family (including Escherichia coli), and Staphylococcus aureus on many of the surfaces tested.
To assess the microbial diversity in house dust, a team of scientists — which was led by Jordan Peccia, a professor of chemical and environmental engineering at Yale University in New Haven, CT — tested samples from 198 homes in Connecticut and Massachusetts.
The researchers found that the most common fungal species were Leptosphaerulina chartarum, Epicoccum nigrum, and Wallemia sebi. The most abundant bacteria were from the Staphylococcus, Streptococcus, and Corynebacteria families.
Homes with pets and those located in suburban areas had more diverse bacterial species, while those with reported water leaks harbored more fungi.
Meanwhile, scientists from Seoul National University in Korea studied the bacteria that inhabit our refrigerators and toilet seats. They found that the many of the bacteria present were also resident on human skin, indicating that we are the source of a lot of the microbes in our living environment.
"In this study, most bacteria detected were probably not pathogens or opportunistic pathogens, and genera belonging to common pathogens were detected in only a very small fraction of communities on the surfaces of refrigerators and toilets," the authors explain.
So, our tiny roommates are everywhere: from our kitchen sinks to our living room floors and toothbrush holders. They key question that remains is what their impact on our health is.
The answer depends on our age, the state of our immune system, and, of course, the individual microorganism in question.
Allergy and hygiene
According to the "hygiene hypothesis" — which was originally proposed by Prof. David Strachan in 1989 — allergic diseases are able to be prevented "by infection in early childhood, transmitted by unhygienic contact with older siblings, or acquired prenatally from a mother infected by contact with her older children."
In an article published in the October edition of Nature Immunology, Profs. Bart N. Lambrecht and Hamida Hammad — from the VIB Center for Inflammation Research at Ghent University in Belgium — explain that studies in animal models have shown that exposure to some viruses, bacteria, and parasites is linked to lower rates of allergy.