As a microbiologist, I’m all too aware that we’re surrounded by airborne microbes. Whenever I work with in the lab, I have to rigorously apply what’s known as “sterile technique,” a set of standards and practices designed to minimize environmental contamination. Even when practicing sterile technique, I find my media, reagents, and tools become contaminated all too often. Given this issue, I often wonder how many microbes are floating around the lab and whether or not they’re dangerous. Today, I’m going to delve deeply into this topic by analyzing sources of airborne microbes and determining the overall effect they might have on humans.
Where do airborne microbes come from?
Microbes can originate from a variety of sources. The most common are described below:
Humans: As my previous posts have shown, humans have a robust microbiome (1). Almost every organ, orifice, and surface in our bodies contain microbes. Since we’re constantly moving, respiring, excreting, and shedding, we have ample opportunity to eject our microbiome into the air.
Animals: Pets and other animals can add microbes to the air for the same reasons that humans do.
Plants: Even though plants are stationary, they undergo many processes that can release the microbes that live within them. Pollen and seeds are designed to move around, and environmental factors like wind, rain, and foraging animals can contribute to release of the microbes within them into the air.
Fungi: Although most microbes are bacteria, many fungi are capable of releasing spores into the air.
Decay/Garbage: Garbage and other wastes may not always be a significant source of microbes, but it often contains food and other sources of energy that can become contaminated with microbes. This leads to concentrated microbial colonies that can continuously release microbes into the air (2).
Dust: Since most dust comes from the sources above, it is not necessarily an original source of airborne microbes. However, dust is important because it can easily be resuspended in air thus giving microbes a second opportunity to become airborne.
Plumbing: Although Indoor plumbing is largely designed to facilitate the removal of sources of airborne bacteria, it’s not a perfect system. Contaminated water can release airborne microbes when sprayed and simple actions like flushing a toilet can release fecal bacteria into the air.
Ventilation: Ventilation contributes to airborne microbes simply because it is designed to move air around. In addition, microbes can grow within improperly cleaned ventilation systems.
Mold: Water damaged houses and other waterlogged materials can be the perfect incubators for fungi. Although these fungi are centrally located on the damp material, their presence has been shown to dramatically increase local airborne fungi levels.
It’s important to note that these aren’t the only potential sources of airborne microbes. For example, a house near a body of water might see high levels of aquatic bacteria in the air (4). However, I wanted to focus on sources that are present in most environments.
What effect do these microbes have on our health?
Determining whether or not these microbes are bad for us is a difficult question. The vast majority of airborne bacteria are harmless, but most studies detect a few pathogens at least. One particularly robust study published in 2015 looked at microbes in dust across the United States of American (4) They detected a variety of strains, many that were localized to different parts of the country.
The figure above shows the relative abundance of the microbe genera Cellulomonas, Terriglobus, Alternaria, and Cladosporium across the United States (4). From all of these samples, the only prevalent pathogen was Cladosporium, a fungi that kills plants a causes asthma, but this genus was one a small portion of the total microbes they detected.
Nevertheless, certain sources of airborne microbes can contain a high number of dangerous pathogens. The simplest example is a sick person. Anyone infected with a disease that can spread by air will eject pathogens by coughing, sneezing, or just being in the area. For this reason, hospitals and other areas were the ill might be congregated have high risks of containing dangerous levels of pathogens (5) Humans aren’t the only source of dangerous microbes either. Waste sites are often tested for hazardous microbes and several studies have found alarming results. One paper showed that bacteria with antimicrobial resistance genes were prevalent at dump sites in India (6) and another has discovered an abundance of Salmonella and other potentially dangerous microbes in the air at wastewater treatment plants (7). Improperly cleaned ventilation systems have caused major outbreaks of Legionnaires’ disease, and mold can often release toxic chemicals (3)
Its important to note that airborne microbes can be beneficial as well. In most cases, this relates to acquired immunity. Many studies have found that exposure to farms reduces asthma, possibly because airborn microbes from animal microbiomes stimulates the development of human immune systems (8, 9, 10). To test this possibility, scientists have exposed mice to farm-derived airborne microbes and tested their immune response to common allergens.
Mouse models showing that airborne bacteria from farms reduce the effect of common allergens. Table adapted from (9)
The table above shows a reduced immune response upon exposure to the farm-derived agents. In other words, these mice were much more resistant to allergens of the bronchia and lung when exposed to airborne bacteria from a farm at a young age or during development. This helps confirm that airborne bacteria may be responsible for the observed allergy resistance in children on farms.
What should we do about airborne microbes?
Since airborne bacteria can be harmful, helpful, or have no effect on human health, it may be difficult to know whether we should reduce or increase exposure to them. In cases like this, I’d recommend the common sense approach. Get rid of rotting wastes, clean your house’s ventilation system every so often and don’t go around hugging sick people, but feel free to pet animals or have consensual sex.
While I was writing this post, I began to wonder just how many microorganisms are in the air we breathe. As I investigated this question, I realized that I delved into a topic worthy of an entirely separate post. Thus, my next article will be a sister post to answer this very question and show how scientists came to their conclusions.
Images
All images used have been labelled for re-use on Google Images or are taken directly from the publication. If any image owner has an issue with this article, please contact me and I will address the issue.
Images not referenced within the text come from the following sources (in order):
Face Masks: https://udn.com/news/story/3/2294594
Sneeze: https://en.wikipedia.org/wiki/Surgical_mask
References
(1) https://en.wikipedia.org/wiki/Human_microbiota
(2) http://pubs.acs.org/doi/pdf/10.1021/es0223426
(3) https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4688924/
(4) http://www.pnas.org/content/112/18/5756.full
(5) http://journals.sagepub.com/doi/pdf/10.1177/1420326X03012001002
(6) http://www.isca.in/IJENS/Archive/v3/i10/7.ISCA-IRJEvS-2014-166.pdf
(7) http://www.sciencedirect.com/science/article/pii/S0043135409001602
(8) https://www.ncbi.nlm.nih.gov/pubmed/18572111
(9) https://www.nature.com/articles/nri2871
(10) http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2222.2000.00799.x/full
About the Author
I’m a research scientist living in the suburbs of Boston. I recently left academia to work in in industry, but I miss teaching so I decided to start writing articles on interesting discoveries in the world of microbiology. My goal is to uncover subjects that are unusual, unique, and might one day have a major impact on our daily lives.
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