Airborne microbes: Where Do They Come From And How Dangerous Are They?

Today, you and I will quickly take a look at the topic “Airborne microbes: Where Do They Come From And How Dangerous Are They?”.

This has become necessary as we have sen overtime that several individuals have been searching for topics related to the above topic Airborne microbes: Where Do They Come From And How Dangerous Are They?.

However, if you are among those that have been searching for answers to [airborne microorganisms, list of microorganisms found in air, airborne bacteria in home, types of microorganisms in air, microorganisms in air wikipedia, list some types of microorganisms found in the atmosphere, airborne bacterial diseases, airborne bacteria definition, Airborne microbes: Where Do They Come From And How Dangerous Are They?], then you can see that you are not the only one.

Nonetheless, you shall get all this information right here on this blog.

Airborne microbes: Where Do They Come From And How Dangerous Are They?

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.

Most of the information above was derived from an excellent review on the subject written by Aaron J. Prussin and Linsey C. Marr (3). That review is open access so please check it out if you want more information.

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.

How do we assess airborne microbes?

Before we determine the number of bacteria we inhale, it is necessary to understand the different ways we can assess airborne microbe levels. Scientists have developed a number of ways to collect bacteria and fungi that are dispersed in the air, each with varying levels of accuracy. Below, I’ve listed some of the more common techniques

Agar plate exposure (1):

This is the easiest method to perform. An agar plate is exposed to air for a specific amount of time.

The plate is then closed, and any microbes that landed on the plate are allowed to grow into colonies for several days.

Scientists can count the number of colonies that grow after a certain period of exposure to estimate the number of bacteria in the air and can analyze colony morphology to identify them

. This method is quick, cheap, and can be useful to a lab by showing the probability that media or other chemicals will become contaminated if exposed to air.

Unfortunately, this method is also quite inaccurate.

The number of bacteria that have a chance to land on the dish can vary widely depending on air currents and the location of the plate.

Additionally, not every microbe that lands on the plate will develop into a colony.

Some might not be compatible with the growth media or might grow too slowly to become a colony. Thus, scientists needed to develop methods with a higher degree of accuracy.

Impingers (1, 2)

Impingers are devices that push air through a liquid medium designed to capture bacteria.

The liquid can then be analyzed for bacteria either by microscopic analysis, culturing, or more advanced methods.

This is more accurate than agar plating because you can regulate the volume of air sampled, but it is not perfect because the liquid medium can damage microbes.

Impactors (1, 2)

Impactors are similar to impingers in that they push air at a medium designed to capture bacteria. However, with this instrument, the media is solid instead of liquid.

The media can come in multiple forms, such as an agar gel to allow bacterial cultures to develop, or a water soluble membrane designed to pool bacteria for qPCR. As with the impingers, this device is not perfect because the collection method can damage organisms.

Filtration

With filtration, air is pumped through a membrane, such as polycarbonate or cellulose acetate.

The filter membrane allows air and other small molecules to pass through, but is small enough to trap microbes.

This technique is generally the most accurate, but it tends to be the least cost effective and difficult to use. As a result, it is mostly used by researchers rather than for routine air quality tests.

Different sized membranes can be used to trap different sized microbes as well.

Of these available methods, I want to find a study that uses the filtration technique because that is the most accurate available.

I’m also consciously deciding to focus on just bacteria in the air rather than all microbes (bacterial, fungal, and viral) to simplify things.

See Other Articles People Are Reading

• Cry Me A River – From Biology To Psychology Of Tears
• Redefining ‘Health’ For The 21st Century | Health Care Changes In The 21st Century
• Missile Technology – The Weapon Of Destruction
• Discussing Day-to-Day Fear | Types Of Fears & How To Overcome Them
• Electromagnetism – Antenna Radiation Patterns | How To Read Antenna Radiation Patterns
• Do Robots Really Have Emotions? | Can Artificial Intelligence Feel Emotions?

So how many microbes are in the air?

Alright, now for the fun part where we get to do a deep dive into a paper.

The paper in question, “Total Virus and Bacteria Concentrations in Indoor and Outdoor Air” was written by the Marr Lab at Virginia Tech in 2015 (4).

This lab is dedicated to studying air quality and the first author, Aaron J. Prussin, has a number of papers focused on airborne microbes.
As the title suggests, the goal of this work is to assess airborne microbe levels across different locations.

authors traveled to several areas (classrooms, houses, outdoor areas, etc.) and used the filtration method described above to collect bacteria and viruses.

They then stained the filter with a dye called SYBRGold that becomes fluorescent when it interacts with DNA or RNA. They looked at the filter with fluorescence microscopy to detect patches of nucleic acid.

Each patch was assumed to indicate a bacteria or virus. Since a virus is much smaller than a bacterial cell, they were able to easily distinguish between the two types of organisms by size.

Finally, the authors divided the number of organisms on the filter by the volume of air passed through the filter to calculate the airborne bacteria and virus concentrations in each location. The results are shown in the table below.

Airborne virus and bacteria concentrations in different environments. Keep in mind these numbers indicate tens of thousands per cubic meter. Adapted from (4).

In looking over this table, I noticed a few interesting observations.

For one, indoor environments had similar levels of bacteria and virus particles.

The most sterile appeared to be the health center, possibly because such areas are kept as clean as possible to prevent cross-contamination between sick individuals.

I also noticed that the outdoors was significantly different from the average indoor space in that the total concentration of airborne microbes was higher and there was a greater proportion of virus particles compared to bacteria.

Most importantly, this study is exactly what I needed because it gives us very clear numbers for the airborne bacterial concentrations indoors and outdoors. I believe that these numbers are accurate because they are close to the numbers determined by other similar studies (5, 6).

Before I move on, I wanted to mention a few other cool studies that analyze airborne microbes.

Many studies are more concerned with the identity of airborne microbes rather than their quantities. In the paper “Chamber Bioaerosol Study: Outdoor Air and Human Occupants as Sources of Indoor Airborne Microbes” (7), the authors collected bacteria and fungi on a filter paper like in the previous study, but decided to identify them by DNA sequencing rather than quantitate them.

Identification was accomplished by extracting DNA from the filter and sequencing all copies of the bacterial 16S rRNA gene and the ITS1 region of the fungal rRNA gene.

These genes are highly conserved among related organisms and can be used to classify organisms into different taxa. I’ve described this technique in detail before so I’m just going to link to that description here.

The relative abundance of the most common fungal and bacterial taxa in indoor and outdoor air Adapted from (7).

Ultimately, the authors were able to show that indoor and outdoor air contained different species of airborne microbes, and some taxa were abundant over others.

For example, the fungi Battarrea steveni was abundant in indoor air samples, but barely detected in outdoor samples. However, they were unable to obtain quantitative data from this information.

^{I wonder how many bacteria have landed on the Mona Lisa? (IMG SRC 2)}

One other study I want to mention is the “Stability of airborne microbes in the Louvre Museum over time” (8). There isn’t anything special about this paper from a scientific perspective.

It uses typical methods to quantitate and identify bacteria in an enclosed space over the course of 6 months. It’s just the fact that this study is done in the most famous art museum in the world that fascinates me.

Why would the authors want to know how many E. coli are floating around the Mona Lisa? Were petri dish cultures confused for fine art? Did the authors finally solve the Da Vinci Code? Well, I don’t have an answer to any of these questions because the full paper is locked behind a paywall.

So how many microbes do we breathe in each day?

Alright, so we have an approximate number for the concentration of bacteria in the air: 51,000 cells per cubic meter indoors and 84,000 cells per cubic meter outdoors.

Again, I’m not including any virus or fungi in this count for the sake of simplicity.

Now all we have to do is multiply this number by the volume of air we breath in a day to get the number of cells we inhale daily.

Determining the volume intake of an average human wasn’t too difficult.

A quick google search revealed a study by the California Environmental Protection Agency (9) that focused on this exact question. I’m not sure why the Ca EPA needed to do this study, but it certainly helps me out.

According to this study, an average adult male inhales about 8 liters of air per minute while resting. This comes to ~11,500 liters 11.52 cubic meters per day. Assuming this ideal man spends his entire day resting indoors, his bacterial intake will be…

590,000 Bacteria Per Day!

Almost 600,000 bacteria per day, and that’s just if the guys sits down indoors all day playing video games. If he sat around outside his intake would increase to about 970,000 per day.

That’s almost a million bacteria in a single day and the guy isn’t even walking around.

Now a million bacteria in a day seem like a huge number, but before you run out and buy a lifetime supply of facemasks, keep in mind a few things.

Most airborne bacteria are harmless, not all inhaled bacteria would adhere to the lungs, and even fewer would be able to grow.

Furthermore, one million bacteria pales in comparison to the estimated 100 trillion bacteria of the human microbiome (10).

Still, I wouldn’t have guessed the amount of airborne bacteria we inhale each day to be as high as it is.

This project took a bit longer than expected, but I’m happy with the result.

I’m also pretty confident in this number as multiple sources seem to back up the concentration of airborne bacterial and daily air intake of an average person.

At any rate, I certainly learned an interesting fact and I hope you did too.

That”s the much we can take on the topic “Airborne microbes: Where Do They Come From And How Dangerous Are They?”.

Thanks For Reading

O3SCHOOLS TEAM

See Other Articles People Are Reading

• Cry Me A River – From Biology To Psychology Of Tears
• Redefining ‘Health’ For The 21st Century | Health Care Changes In The 21st Century
• Missile Technology – The Weapon Of Destruction
• Discussing Day-to-Day Fear | Types Of Fears & How To Overcome Them
• Electromagnetism – Antenna Radiation Patterns | How To Read Antenna Radiation Patterns
• Do Robots Really Have Emotions? | Can Artificial Intelligence Feel Emotions?