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Do HypoAir products kill the “good” bacteria as well as “bad” bacteria?

Short answer: yes, some good bacteria are killed, but let us explain a little about the nature of bacteria, and how this technology affects them!

Since HypoAir’s bipolar ionization is made for the home, we are talking about “good” bacteria for humans, found on exposed home surfaces, the skin, and upper respiratory tract, because this type of ionization does not penetrate to interior surfaces.

So the answer is: yes, bipolar ionization does kill some “good” bacteria, but the type of bacteria, on which surfaces, at what humidity, at what concentration of ions, and so on, are highly variable!   We find that the biological and air quality contaminants found in homes are typically in high unhealthy concentrations, which are typically not found in the outside air.   We want to reintroduce natural counterbalances to suppress the spread and growth of these biologicals indoors, to make them more similar to what's found in nature.  However, our technologies are not going to sterilize the environment; they're just designed to cut concentrations and reduce illness in families.  In 20-30 years, technologies like ours could become very cost effective and installed throughout a home to have a nearly sterilizing effect in our indoor environments.  We don't want that!  At that point, the intentional reintroduction of a positive biome would be advisable.  If you are concerned that the use of bipolar kills too many good bacteria, you may want to investigate probiotics for the air to replace those good bacteria on surfaces, and use gentle cleansers and soap for your skin, dispensed from containers that don’t promote the growth of bacteria.  And, consider the fact that pets (and dogs especially) vary the nature of your home’s microbiota a lot too!  

Getting back to bacteria, here’s a short refresher from an article about bacteria, endotoxins and exotoxins:  bacteria can be classed into two different groups: “Gram-negative” or “Gram-positive”.  These classes are based on a test developed by scientist Christian Gram in 1884, which differentiates the bacteria using a purple stain.   According to webmd.com, bacteria either have a hard, outer shell, or a thick, mesh-like membrane called peptidoglycan.  The hard outer shell will resist the purple stain, and show up as a red color.  These are called “gram negative” because the purple stain did not show.  Bacteria with the peptidoglycan absorb the purple stain much more easily and are called “gram positive”.  The stain also tells many more characteristics about the bacteria and the way it interacts with bipolar ions.

Bipolar technology is also called cold atmospheric-pressure plasma (CAP), or non-thermal plasma (NTP).  In a study which analyzed how plasma affected bacteria in soil, it turned out that the non-treated soil consisted of both gram-positive and gram-negative bacteria from different phyla (a level of classification).  After treatment with plasma, however, the gram-negative bacteria were mainly eradicated, and only the major phyla of Firmicutes (gram-positive) were left.  Presumably this has to do with the structure of the bacteria.

The authors cited two previous studies on treatment of E. Coli (gram-negative) and S. Aureus (gram-positive) with cold plasma.  In the first study, the treated Gram-positive bacteria was mainly inactivated by intracellular damage, while the Gram-negative bacteria expired mainly by cell leakage.  The second study showed that plasma treatment led to damage of the bacterial cell wall of both E. coli and S. aureus and a decrease in the total concentrations of nucleic acid and cellular protein. However, S. aureus (gram positive) was less susceptible to plasma exposure in comparison to E. coli (gram-negative).

The sum of these three studies seem to indicate that gram-positive and gram-negative bacteria are affected by plasma differently, and chances of survival of bacteria after treatment with cold plasma is higher if a bacteria is gram-positive, having more of the mesh-like membrane (peptidoglycan).  One can see from the diagrams below that these peptidoglycan layers are relatively thick on the gram-positive type, which may account for its resistance to plasma.  Depending on the relative humidity of the air, plasma can form varying quantities of reactive oxygen species such as hydroxide ions (OH-), hydroxyl radicals (•OH), atomic oxygen (O), hydrogen peroxide (H2O2), and singlet oxygen (1O2).   Ozone (O3) is another ROS formed by plasma generators, however we’ve excluded it from HypoAir ionizers by limiting the input energy.  These ROS are reported to damage the bacterial structure and functions.  In addition, the multiple reactive nitrogen species (RNS), including nitric oxide (NO), peroxinitrites (ONOO−), nitrites (NO2−), and nitrates (NO3−), can play a major role in the plasma’s biocidal process by altering the cell wall components, the functions and the structure of the phospholipid bilayer, the structure of nucleic acids and cellular proteins, gene expressions, and protein synthesis. (Effects of Atmospheric Plasma Corona Discharges on Soil Bacteria Viability)

Image source: Difference between gram-positive and gram-negative cell wall

However, there are factors other than gram-type that affect bacterial eradication via plasma technology, such as pH, humidity, and the surface on which the bacteria were placed during plasma exposure.  Specifically, 

• Lower pH can translate to higher kill rates.  A reduction of 4.9 log was observed when Bacillus cereus was treated at pH 5, while a reduction of only 2.1 log was observed at pH 7.  Interestingly, the same study showed that “No appreciable differences between gram-positive and gram-negative pathogens were observed, although the spore-forming B. cereus was more resistant to plasma than non-spore-formers.” (Spores in bacteria are not the same as mold spores; only one bacteria makes one spore). 
• Humidity was also reported as an important parameter; increasing the relative humidity was correlated to efficiency in plasma inactivation of Aspergillus niger, which was explained by the generation of more hydroxyl radicals. However, the same study showed that “In contrast, B. subtilis showed slightly poorer inactivation at high gas humidity.”
• Regarding the surface on which the bacteria were placed during plasma treatment, higher eradication was observed when microorganisms were loaded on a filter compared to a fruit surface, because the microbes could “migrate” to the interior of the fruit.  Therefore, if the bacteria could migrate into a moist surface, it was more likely to survive. (Cold Atmospheric Plasma Disinfection of Cut Fruit Surfaces Contaminated with Migrating Microorganisms)  Wow, bacteria can migrate! 

Now that we know that there are a lot of variables in your home that affect the mortality of bacteria, how likely is it that “good” bacteria on skin, your upper respiratory system, and home surfaces will be killed?

First of all, let’s look at what types of bacteria these are.  Staphylococcus epidermidis (phylum Firmicutes, gram-positive)  is a part of the skin microbiota (aka skin flora) and another type of good bacteria is Roseomonas mucosa (phylum pseudomona dota, gram-negative), which is naturally present on the skin and contributes to an overall healthy skin microbiome. (Dermatologists Break Down the Difference Between Good and Bad Bacteria)  In addition, the optimal pH value of skin on most of our face and body lies between 4.7 and 5.75, which is mildly acidic. (Understanding skin – Skin’s pH)  According to the studies above, it’s not known whether good bacteria on healthy skin survive plasma treatment, because although healthy skin is normally mildly acidic (which promotes their death by ions), moist skin favors preservation of good bacteria. Therefore, no matter what relative humidity is in your home, it’s a good idea to keep your skin hydrated!  

Concerning the upper-respiratory tract, potential keystone microbiota are Dolosigranulum and Corynebacterium species (both gram-positive), as they have been strongly associated with respiratory health and the exclusion of potential pathogens, most notably Streptococcus pneumoniae, in several epidemiological and mechanistic studies. (The microbiota of the respiratory tract: gatekeeper to respiratory health)  Regarding pH, airway surface liquid pH in normal airways ranges in vivo between 5.6 and 6.7 in the nasal mucosa, and is around 7.0 in bronchia.  (Airway Surface Liquid pH Regulation in Airway Epithelium Current Understandings and Gaps in Knowledge) Therefore it’s mildly acidic in the upper regions, and tending toward neutral pH in the lower regions.  Being gram-positive favors survival, as does being in mucous, but being on a mildly acidic surface favors eradication of these good bacteria.  Again, keeping your mucous membranes moist via water intake and plain saline sprays is a good idea!

Finally, most of the ions that are emitted by bipolar devices will contact surfaces in our homes.  What kind of good bacteria live on surfaces?  Forty homes in North Carolina were sampled for a study in August 2011.  Standard places like cutting boards, kitchen counters, door handles, toilet seats and pillowcases were sampled.  The bacterial families with the highest relative abundances across all of the collected samples were the Streptococcaceae (8.9%) (gram-positive), Corynebacteriaceae (5.6%) (gram-positive), and Lactobacillaceae (5.1%) (gram-positive).  Since these are all gram-positive, their survival would also depend upon the acidity and nature of the surface.  Keeping the humidity in the home in the sweet range of 40-60% will favor the production of more bacteria-killing hydroxyl radicals, and cleaning regularly is important.  Wet, dusty or cluttered surfaces will actually promote good bacteria survival, but they also promote bad bacteria survival too, so to play it safe, it’s best to keep surfaces clean!  

What’s the difference between dangerous mold and good fermentation?

Maybe you’ve heard about fermented foods as one of the latest health fads, and are wondering (like I was), what’s the difference between green cheese discovered in the back of the fridge, and “good” stinky cheese, kombucha or sauerkraut?  They all seem to use microbes to change the flavor, so how can we tell the difference?  

Fermented foods are defined as “foods or beverages produced through controlled microbial growth, and the conversion of food components through enzymatic action” (my emphasis, from 2016 study).   The main difference, it turns out, is the intention and methods (control) of allowing food to ferment.   Fermented foods have been around for a loooong time.  When you have foods that are notoriously difficult to preserve (dairy) in a hot climate (the middle east and Africa), fermentation happens naturally and quickly.  As long ago as 10,000 BCE, people figured out how to control the natural bacteria present in cow, sheep, goat and camel milk to produce yogurt.  This is called “thermophilic lactic acid fermentation”. (Living History Farms)  This continued for centuries and in 1910, a Russian bacteriologist, Elie Metchnikoff, attributed the longer average lifespan of Bulgarians (87 years) to increased fermented milk consumption, and a particular strain of bacteria used in their fermented milk products.  Certain strains of “Lactobacillus bulgaricus” were shown to be able to survive and flourish in the human stomach and intestines, making them the first “probiotics” discovered.   Probiotics simply are live bacteria and yeasts that are good for you, especially your digestive system. (webmd.com)  The “cultures” of live bacteria and yeasts in fermented foods make them full of natural probiotics.  However, ancient peoples (through the 1900s) were likely not eating them for their health benefits.  Fermenting was simply a form of food preservation.  Cheese, bread, vinegar and beer are all products of fermentation.  Food can be fermented naturally using the microbes that are present in the food itself, or by adding a “starter culture” that has the desirable microbes included. (2019 paper)

Many studies have been conducted on the health benefits of fermented foods.  Some have been proven, and others are disputed.  For example, compounds known as biologically active peptides, which are produced by the bacteria responsible for fermentation, are also well known for their health benefits. Among these peptides, conjugated linoleic acids (CLA) have a blood pressure lowering effect, exopolysaccharides exhibit prebiotic properties, bacteriocins show anti-microbial effects, sphingolipids have anti-carcinogenic and anti-microbial properties, and bioactive peptides exhibit anti-oxidant, anti-microbial, opioid antagonist, anti-allergenic, and blood pressure lowering effects. (paper investigating the health effects of fermented foods). As a current health hot topic, it’s best for you to do your own research on any fermented food you want to start including in your diet. 

There are many types of fermentation that are culture-specific, having such a strong smell and/or taste that to the uninitiated, may be called “rotten”!  In fact, “one person’s delicious fermentation is another person’s disgusting rot, and according to fermentation guru Sandor Ellix Katz, “Learning a sense of boundaries around what it is appropriate to eat is necessary for survival. But precisely where we lay those boundaries is highly subjective, and largely culturally determined.” (americastestkitchen.com) This is the case for hákarl, an Icelandic delicacy often referred to as “rotten shark”, Surströmming, a Swedish fermented herring product, natto, a slimy fermented Japanese soybean dish, and century eggs, which are fermented for 3 years in some Southeast Asian cultures.  (18 stinky foods around the world).

Okay…we know that heat and microbes will break down food whether or not we initiate it, so just what kinds of “control” can we exert over fermentation?

One key is just as invisible to the naked eye as the microbes themselves: air.  Fermentation is generally an anaerobic process, which occurs in an airless environment. Most desirable bacteria thrive in this oxygen-free environment digesting sugars, starches, and carbohydrates and releasing alcohols, carbon dioxide, and organic acids (which are what preserve the food). Most undesirable bacteria that cause spoilage, rotting, and decay of food can’t survive in this anaerobic environment. (Living History Farms)  Unfortunately, this reference does not point out at least one major exception: Clostridium botulinum, which produces botulism.  In order to keep vegetables from developing undesirable mold, for example, they are “weighed down” under the fermenting liquid so the food does not contact the air. 

According to Paul Adams, a researcher for America’s Test Kitchen,  we have a few other tools to keep the fermented product safer and less smelly:  salt, temperature and acidity.  For example, allowing cucumbers to sit in room temperature water will usually produce a scummy pink slime in short order, but changing the water for brine (saltwater) will produce some nice tangy pickles.  Brewing beer has its best results when controlling the temperature, so brewers have developed methods to decrease or increase the temperature of their kegs depending on the ambient air temperature.  Finally, acidity is a tool for controlling fermentation.  pH is the measure of acidity or alkalinity in a solution and pH changes due to changing chemical composition produced during fermentation.  pH also can control the species of microbes in fermentation.  For example, the low pH (acidity) of kombucha, owing mainly to the production of high concentration of acetic acid, has been shown to prevent the growth of pathogenic bacteria such as Helicobacter pylori, Escherichia coli, Salmonella typhimurium and Campylobacter jejuni. (2019 paper) According to Utah State University Extension Service, for fermentation to be successful at eliminating all potential pathogens, the pH level must drop below an acidity of 4.6 verified by using a pH meter or test strip.  Foods that “appear” to be safe can still contain harmful pathogens.

What’s the difference between yeast and mold?

Yeasts and mold are both considered fungi.  Yeasts are microscopic fungi consisting of solitary cells that reproduce by budding. Molds, in contrast, are multi-cellular and occur in long filaments known as hyphae, which grow by apical extension (extending into fresh substrate). Yeasts do not produce spores; molds do.  Yeasts can grow in aerobic (with air) or anaerobic (airless) conditions; molds only grow in aerobic conditions.  Regardless of their shape or size, fungi are all heterotrophic (cannot produce their own food) and digest their food externally by releasing hydrolytic enzymes into their immediate surroundings (absorptive nutrition). (Introduction to Mycology textbook) Here is a highly magnified photo of the two:

Photo source: microbenotes.com

As a company concerned about air quality, HypoAir is typically anti-mold except where it’s cultured and processed carefully for medical and gastronomical reasons (like penicillin and cheese)!   Penicillium (P.) roqueforti, P. glaucum, and P. candidum are some common types of mold that are used in cheesemaking.  (thecheesemaker.com)  I’ve found out through researching this article that there are other types of mold that give fermented food its characteristic flavor and possible health benefits.  For example tempeh, an Indonesian fermented soybean cake, and Miso, a traditional Japanese paste of fermented soybean used to make miso soup, both contain molds that have no detrimental effects to humans.  Likewise, yeasts are familiar to those who make bread, but Kombucha, a fermented tea beverage reported to have originated in northern China, is also made with yeast.  The critical aspect of making each of these foods is providing the correct environment, including temperature, pH, humidity and salinity, to encourage the good fungus and discourage bad fungus!

Of course, there is a lot of information on the internet about making fermented foods at home.  Not all of them advise the safeguards that are necessary to prevent harmful bacteria from giving you life-threatening food poisoning, so it’s best to compare them to a source such as the USDA.  For example, this guide on safely fermenting food at home recommends starting fermentation only on fresh, clean vegetables and using non-iodized salt.  In addition, the National Center for Home Food Preservation has tips and tested recipes.

If you have any doubts about the safety of fermented food, throw it out!  The website fermentools.com gives the following advice on when to do so:

• Visible fuzz, or white, pink, green, or black mold.
• Extremely pungent and unpleasant stink.
• Slimy, discolored vegetables.
• A bad taste.  If your taste buds are offended, be safe and spit it out!

If you follow the safety guidelines, you can explore the world of fermented foods and maybe even make your own food combinations to surprise family and friends! (Who wouldn't like a delicious jar of well-preserved food?)