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Photograph of a mold culture plate home test kit for mold. Validity of Mold Culture Tests

Mold culture test kit accuracy:

Are culture plates a reliable method to screen buildings for indoor mold contamination? This article discusses building mold tests that rely only on settlement plates or swabs to find toxic mold in buildings. Before you buy any "mold home test kit" for mold you should read this article.

This article explains the limited accuracy of mold cultures when used as "mold test kits" to examine indoor air quality as an investigation methodology in searching for possible causes of respiratory illness, asthma, immune system disorders, rashes, skin disease, psychological and neurological disorders, eye infections, or other symptoms that may have a physiological and environmental component.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Problems With Relying on cultured mold samples to evaluate a building

Ulocladium and other molds in culture © D Friedman at InspectApedia.com If you smell mold or see mold in a building, most-often you do not need to "test" for mold contamination. Find and remove the mold, and fix the leaks that caused its growth.

A thorough visual inspection by an expert along with a collection of the leak history of a building, occupant indoor air quality complaints, and particular health vulnerabilities of occupants should produce a finding that either asserts that further mold work is not needed OR a report that outlines what mold cleanup and building repairs are needed.

Despite the inaccuracy of such tests, many consumers seek a "mold test" to screen for indoor mold contamination.

Why don't we use readily-available mass-marketed cultures, settlement plates, and swab kits such as those available at the local hardware store?

Watch out: While all "mold tests" and "mold test kits" or mold sampling methods have their limitations, the usefulness of mold culture plates as a general screen for harmful indoor mold contamination is particularly limited, inaccurate, and most-likely to give at best an incomplete picture of the indoor air environment.

OPINION: because of the 100,000 mold species known and the estimated 5.1 million mold genera/species on earth, most mold genera / species - about 90% of them - simply will not grow in any culture. (Haines 2016).

So even if the culture does successfully grow mold we don't know if this accurately represents what mold contaminants are in the building tested.

The underlying methodology of this test may be seriously flawed if you're relying on the results of culturing to characterize just what problematic fungal spores are present in a building.

Mold cultures, typically taken using settlement plates, Anderson-type samplers, and sterile swabs, can be quite unreliable as indicators of what's really present in an indoor environment.

This is especially true if the test does not detect a mold problem (one may be present but was not detected by this method) and it might be true even if the test does seem to detect a problem as it may detect molds other than the largest or most serious mold contamination reservoir that's present.

As another test limitation example, a dead spore in the air may be toxic or pathogenic (containing mycotoxins for example) but that spore may not grow at all in a culture medium.

In addition, variations in building indoor air movement, activity, humidity, temperature, and other conditions causes an enormous variation in the level in air of all sorts of indoor particles. I have found as much as four orders of magnitude in the level of airborne mold spores as these conditions in buildings were changed.

And individual mold spores, varying by size, mass, toxicity, and preference for mold culture, find very different rates of first settlement out of the air onto any building surface (including a culture plate) and second rates of growing within any given culture medium (including a range of growth from abundant to zero).

... culture-based methods likely will not work except for very hardy microbes [Farnsworth et al. 2006]

...Fungal spores have physical diameters of about 0.5 to 30 µm or larger, while the aerodynamic diameters of airborne fungal spores and spore clusters are reported to be from 0.9 to 5 µm [Eduard 2009; Hussein et al. 2013; Reponen et al. 2011b].

You can see that a culture that grows only some mold species can be particularly misleading, even dangerous to rely upon when investigating building-related illness.

Mycotoxin-producing and pathogenic species have to be detected specifically, however, because of their higher toxicity. - Eduard 2009.

In our mold culture photo above you see a "home test kit" for mold collected in a Washington DC apartment in the Watergate. Apparently there are about seven different mold genera/species appearing on this "overgrown" culture plate.

But the fastest growing molds (those who most like the media) will of course overgrow and hide other mold spores that may have landed on the media. And then, heavier larger spores tend to settle out of air sooner than smaller lighter spores. So the culture plate may over-represent heavy large molds compared with the actual molds present in the building.

Use of cultures as building screens for the presence or absence problematic mold is unreliable - only 10% of all molds of any genera will grow on any culture under any circumstances, so a mold culture screening test for mold is 90% wrong at the outset. More so if one considers that certain molds that can be grown in culture only respond to specific culture media.

Even if a mold is grown on a culture, given these constraints one cannot reliably infer that the mold grown is the problem material in a building. Therefore no screening test by air or culture is an adequate substitute for nor superior to the value of a careful visual inspection by an experienced inspector who knows where mold is likely to grow and what it looks like on or in building surfaces and cavities.

Other serious flaws include inconsistent presence of problematic particles in building air, variations in particle settling rate out of air, variations in growth rates on different media of different mold species (fast growing spore A over-grows and hides the presence of slow growing spore B) and the fact that some problematic spores which could be hazardous to building occupants simply do not grow at all in the culture medium.

There is indeed a valid place for cultures (air or swab) in the arsenal of building investigation tools (cross check on visual inspection and bulk sampling, cross check on clearance inspection and sampling, and elaboration of dormant particles).

Also see SWAB TEST KIT PROCEDURE

Culture methods for fungal spore determination are an important tool, but these methods should not be relied-upon as the principal means for determining what problematic particles are in indoor air.

Relying on over-the-counter home test kits for mold to evaluate a building

Stachybotrys spores (left) and structure (right)

Home test kits for mold are inexpensive, easily available, and easy to use. Therefore we wish we could say they could be an OK place to start, but we don't think this is the most accurate approach to screening a building for mold.

In a recent field experiment we used an over-the-counter "mold test kit" according to its instructions while we also performed a professional inspection of the building.

Among problems which our inspection discovered in the building the settlement-plate culture "toxic mold test kit" successfully found an Aspergillus sp. presence.

It also found some nice Alternaria sp. spores, as well as the usual other collection of common Cladosporium species found in air.

What the mold test kit failed to find was what was probably making the occupants in the building sick. Our visual inspection identified various area of mold on surfaces and in the building cavities.

We collected bulk (tape) samples (as well as vacuum samples (such as vacuum samples of fiberglass building insulation) and we also collected some air samples used as a cross-check screen).

A strategic examination of these samples identified a very extensive Stachybotrys chartarum infection in the building, Penicillium, and an extensive Chaetomium globosum colony as well as the Aspergillus and the less troublesome Alternaria and its buddies.

The first two mold species are toxic, the last, allergenic. They were totally missed by the "test kit."

Why did the home test kit for mold fail to find the actual problem in the building?

In addition to our bulk samples (which found the mold missed by the "home test kit") we also used two different types of air sampling machines as well as pulling some vacuum samples of suspect carpeting in an area which looked pretty clean.

Remarkably, our air samples confirmed the Stachybotrys chartarum presence, a spore not so easily found in air, despite the fact that we did nothing more than walk across a carpeted room during the test.

Mold spores may appear or fail to appear in an air test or "spore trap" for mold because of significant variations in particle disturbance during activity in the building, though there is a huge number of other factors which affect air and particle movement inside.

We provide more details about air movement in buildings

at ACCURACY OF AIR TESTS for MOLD

In this building the owner had begun a do-it-yourself demolition and repair of a water-damaged bathroom. Extensive mold contamination was on the exposed side of bathroom drywall and more extensive mold was growing on the cavity side of these walls.

As the owner used a hammer and hatchet to smash and remove drywall, considerable levels of airborne mold were produced - a condition probably more hazardous to the occupants than when the mold was simply growing on and in surfaces and cavities.

We are often able to spot a building where there has been a previous demolition of moldy materials by examining dust from remote surfaces.

The actual exposure level of the building occupants to this mold is not something one can immediately infer from finding leftover traces in a building, but if professional containment and remediation measures were not followed, there is at least a risk that for a time the occupants may have been breathing some pretty moldy air.

In the case described here, the owner who performed the demolition developed a rather ugly skin rash that appeared to be mold-related, and which abated after a combination of treatment and some proper housecleaning.

Personal Field Experience Finds Wide Variation of Airborne Mold Spores over Short Time Intervals

Really? While Pasanen (1991) found that

The relative humidity of air had no direct influence on the growth of fungi.

By repeated measurements of airborne mold levels of a species of Aspergillus sp. at the same location on successive days during a process of dehumidification in a moldy library basement, I found that the level of airborne Aspergillus sp. spores ranged from barely detected (counts in the tens of spores per liter of air) to very high (tens of thousands of spores per liter of air) as the indoor relative humidity fell.

I posit that the very thick mold visible on books in this historically very damp space consisted in, among others, Aspergillus sp. that began to release its spores at dramatically increased levels as the area began to dry.

Most mold species have not been named nor studied

Fuligo septic  (C) Daniel FriedmanOf over 5 million mold genera/species currently estimated to be growing away on earth, less than 100,000 individuals have been named and studied at all.

Less than two percent of all molds have been studied. (Blackwell 2011)

And mold is everywhere, even inside the U.S. Laboratory module of the International Space Station, (Vesper 2008).

Happily for people cleaning up a mold problem or diagnosing a medical or allergenic mold problem, we can do a little better.

There are probably about 200 common mold genera/species that are often found indoors growing in or on building materials.

While there are many others who may make an occasional appearance, even as a large area of mold growth, most often it's one of these 200 or so molds.

Therefore, while in general only about 10% of molds may grow in a culture medium, the number of common indoor molds that can be cultured is probably greater.

Still there are better approaches to screening a building for indoor mold contamination. A visual inspection by an expert is the most-critical service. To support a claim that there was or was not cross-contamination during the subsequent mold remediation job, a few settled dust samples may permit "before and after" mold tests.

Surface Dust & Tape Sampling: An Alternative to Mold Cultures & Speciation for Building Screening Tests

We prefer collecting physical samples of representative settled dust as that will collect both viable and non-viable mold spores. We cannot perform accurate quantitative analysis of a surface or tape sample but we can recognize when there is an unusual level of a particular problem particle, mold or otherwise.

See TAPE SAMPLING PROCEDURES

Keep in mind that except for special circumstances (medical need, need to prove that other building dust is due to improper dust containment during a mold remediation) we do not need to know the mold's name to clean it up.

Except for cosmetic (harmless) black mold that we sometimes find on framing lumber, we want the indoor mold to be cleaned-up (removed) and we want the cause for its growth to be corrected.

See also COSMETIC MOLD, RECOGNIZE

Research on Accuracy of Mold Culture Testing for Indoor Mold Contamination

Question: Where Can I Buy Mold Test Kits for do-it-yourself testing?

I will be calling one of the testing inspectors that you list

at MOLD & ENVIRONMENTAL INSPECTORS .

In addition, is there any device I can purchase which would allow me to make an independent test? - Thanks J.O.

Reply:

Do-it-yourself mold tests are widely available at hardware stores and building suppliers as well as online. The tests usually fall into one of two groups:

Adhesive tape collection surface particles: particle or surface debris or suspected mold on a surface - see https://inspectapedia.com/sickhouse/Adhesive_Tape_Particle_Test.php for detailed procedures on how this test sort is used (to avoid any conflict of interest, or even an apparent conflict, don't sent your sample to us)

Mold culture kits: a plastic petri dish of growth medium is exposed to air, re-sealed, and you or the lab gets to see what grows. Since 90- 95% of molds won't grow on any culture, this is an unreliable way to screen a building for problem mold, though cultures do have widespread and valid use in the lab.

Even in a test or research lab where there are reasons to culture mold the technician needs to select the proper mold culture media that is likely to support growth by the particular classof molds under study.

MEA or Malt Extract Agar is a common culture medium and PDA or Potato Dextrose Agar is another that will grow quite a few but nowhere near all fungii.

But to try to use cultures to grow a mold sample that's been collected by some means, lab experts would typically use a whole battery of various culture media with or without certain mold inhibitors (to control rapidly-growing mold from over-growing other molds in the sample, thus obscuring their presence).

MOLD CULTURE TEST KIT VALIDITY has details.

Airborne tests for mold are not usually performed by a building owner as special equipment is needed.

See ACCURACY OF AIR TESTS for MOLD and for more detail,

AIRBORNE PARTICLE TEST SAMPLING CASSETTE STUDY

and AIRBORNE MOLD SPORE COUNT ACCURACY.

And frankly, for serious mold or water damage investigation cases, using any of these "mold test" methods to produce useful results needs to be combined with an expert building inspection and case history as well as occupant interview.

At ACCURACY OF AIR TESTS for MOLD we provide details about the accuracy of various mold test methods.

The reliance on mold "tests" without a thorough, expert onsite inspection, history taking, etc. is simply unjustified. And that may be why whomever you paid to do these tests can't be more helpful to you.

Properly, and providing an onsite investigation was justified in the first place then the person who inspected the site, took its history, understands the building, its occupants, its environment, should be able to make a meaningful interpretation of various tests done in the building that supplement the more thorough site investigation.

See MOLD / ENVIRONMENTAL EXPERT, HIRE ?- when to hire a mold expert.

Relying on a mold "test" is profitable for the test company and lab but by itself, can be misleading, especially where low numbers or low mold-level findings were the results found in the test. Even high mold level findings can be misleading as the test may not have detected the most problematic mold present.

All of that said, you can hire someone to read and interpret and discuss your report, and then to suggest further investigative steps that could be helpful.

See MOLD & ENVIRONMENTAL INSPECTORS.

Bottom line: in our experience and opinion, relying on mold tests alone to diagnose a building is a risky proposition.

Special thanks to Dr. John Haines for discussing mold testing & indoor mold frequencies. - Ed. 2016/11/26

References on Use of Cultures to Grow or Study Mold


 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2023-08-21 by InspectApedia Publisher

@John Spoerer,

I am sorry that you wasted money on a "mold test kit" using a culture plate. Roughly 90% of molds won't grow in any culture media at all, so the kit is 90% "wrong" the moment you take off the lid.

Furthermore, the molds that do grow are ones that like the culture media, which does not mean that they're the most significant indoor molds present.

And finally (well it's never the last word), no, we can't identify the mold genera/species from just the appearance of a culture. You'd need to examine the culture with a microscope.

All of that griping aside - if your home has had leaks and water has run in ceilings and walls, especially if those are made using drywall, there is a significant risk that there is mold growth in those cavities as well as in insulation that got wet.

The bottom line of what's needed is to follow the water, find the mold, remove it, and fix the cause.

You report that the roof has been repaired, so what remains is to find and remove the mold, clean the exposed surfaces, then finish the repair.

For older people who may be at more risk - as you are on oxygen - I would take the mold hazard very seriously. The risk is that SOME molds (certainly not all of them) produce small, harmful mold spores that can produce a hard-to-cure fungal lung infection.

Start by asking your doctor for advice and follow that.

Do not let some madman run through the home chopping ceilings and walls willy-nilly, not just because of un-needed cost, but because it could significantly increase the health risk to you both.

What IS appropriate, in my opinion, is a thorough on-site inspection by an experienced mold expert who will look at the history of leaks, of where water went, and the building materials involved.

Based on that work s/he should identify the areas of greatest risk of hidden mold and should investigate those building cavities - often a simple small test cut - a few square inches - is enough to look into the cavity, at the nearby wood framing, insulation, and to examine the back or hidden surfaced of the drywall.

If mold is found there, more-extensive demolition and cleaning will be needed.

I apologize, because I know this is much easier for me to say than for you to do (and afford) but IF significant demolition and cleaning are needed in your rental home, my guess is that your doctor will say you should not remain in the building during that work - again because of health risks to you both.

Please keep me posted on how this progresses, and don't hesitate to ask follow-up questions as needed.

Daniel Friedman

On 2023-08-21 by John Spoerer

My wife and I are senior disabled on social security so funds are very limited. We have lived in this rental house for 12 years and it had a roof leak water through the bathroom walls for years before the roof was repaired.

The drywall would get soft. Anyway, we are both on oxygen now and have breathing problems. I got a mold test kit and followed the directions to a T in the bathroom. Exposed for one hour in a Petrie dish.

Wondering if it is a serious type of mold or not. Thank you for your time.

Mold test kit (C) InspectApedia.com John

This reader's Q&A were originally posted at HOW TO CONTACT InspectApedia.com 



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