Guide to Using Mold Culture Plates or Settlement Plates to Collect Mold Samples
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Advisability of using culture plates to screen buildings for toxic mold
Limitations of mold cultures as a "mold test kit"
Usefulness of culturing for the identification and study of mold
90% error rate in capture of mold genera/species with some mold test methods
Do all molds grow on culture?
Do all mold spores settle out of air at the same rate onto culture plates?
Are all mold spores equally important in mold samples?
Questions & answers about culture plates used for screening homes for mold contamination: home test kits for mold, reliability, alternatives, use.

This article explains the use and accuracy of mold culture plates, settlement plates, and mold test kits based on cultures to collect mold test samples to screen buildings for harmful indoor mold.

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A Guide to Using Mold Cultures or Settlement Plates to "Test for Mold"

15th Annual North Carolina/South Carolina
Environmental Information Association Technical Conference
Myrtle Beach, SC
Daniel Friedman 23 September 2005, Updated 4/14/2009, 2/1/2010, 2/22/2012

This study presents a summary and critique of some popular methods used to examine indoor air quality to test for presence or absence of problematic levels of toxic or allergenic mold or other bioaerosols. We describe and critique specific "testing" or "sampling" methods used to "test" buildings for mold in the course of a building investigation. The appropriateness of testing at all is discussed on this and other pages at our website. Also see MOLD in the PETRI DISH, PHOTOS

In this article series discuss the validity of nearly all of the popular mold testing methods currently in use, pointing out the strengths and weakness of each approach to mold sampling in the indoor environment, beginning with air sampling for airborne mold levels indoors.

The use, accuracy, and reliability of mold culture test kits for screening buildings for mold contamination are discussed at MOLD CULTURE TEST KIT VALIDITY and MOLD CULTURE SAMPLING METHOD Also see Mold Culture Plate Test Errors.

Using Mold Cultures for Home Test Kits for Mold

Mold cultures involve the collection of particles by air sampling pump, by gravity settlement, or by lift from a surface using a swab or tape. Some sampling equipment (Anderson™ spore traps) can collect spores directly into a petri dish of culture medium, and are used for "viable spore sampling in air."

The sample by pump, gravity, tape or swab is in any case applied to one or more petrI dishes of culture media for incubation and subsequent examination of the growth product.

Mold Culturing is useful for genera speciation once you have collected a single or dominant sample whose importance (frequency in the building) you already know.

As a "home test kit" for the presence of problematic mold in a building this is an unreliable method, as we describe below at "shortcomings."

Mold Cultures are useful for:

Identifying the genera/species of a mold which was not readily named by (faster, cheaper) light microscopy
Identifying a problem genera to the species level for medical diagnostic purposes - we .e. pass this (possibly accurate) data along to your doctor if you're sick
Distinguishing apparently similar outdoor mold counts from indoor mold counts of "look-alike" spores that may really be different genera/species

Seven Serious Shortcomings of Using Cultures to Test Buildings for the Presence of Toxic Mold

While this is an important tool which has a place in our arsenal, mold culturing is questionable as a means to characterize a mold risk in a building, particularly if it reports the absence of a mold problem. The objections listed below mean that field investigators must collect samples with some care and interpret lab reports with some caution.

Roughly 90% of all molds on earth will not grow on any culture under any condition. Others are quite difficult to coax into growing on culture, even with careful methods. So if you buy a "home test kit" that uses a single culture plate, you're 90% wrong when you open the container. To be fair, it might be that many common indoor problem-molds will show up in certain cultures, but these numbers still hold.
The toxicity or allergenicity of a specific mold (genera/species/strain) may vary widely depending on what it's growing on. So even a "toxic" building mold might be low or non-toxic when growing on certain substances. Molds that grow on cultures may produce very different structures and have different medical characteristics than when growing in nature or in a building.
Cultures may name the wrong mold as "the problem": Cultures have a high risk of both missing the problematic spore and of indicating that some other spore is the dominant or problem in a building. For example, to speciate one of the more than 100 members of the Aspergillus genera requires culturing the sample on four different media, simultaneously, comparing subtle things like growth rate among morphologically similar species. We believe that virtually no lab uses that troublesome procedure outside of university research and medical laboratories.
Settlement plate cultures (such as "home test kits") rely on gravity, making any comparison of "spore counts" dead wrong - different spores are of different sizes and masses, and settle out of the air at different rates.

This over-states the presence of big heavy spores (like Stachybotrys chartarum) and under-states the presence of small light spores (like Aspergillus versicolor) in a given sample.

These small spores (2-3u) tend to stay airborne due to very slight indoor convection currents (e.g. heat from lighting and natural building stack effects).

Our lab photo shows two different mold colonies growing on a culture plate where individual spores settled out of the air onto this surface.
Swab and tape samples for cultures may collect the wrong mold. Swab or tape samples used for culture for identification of what's on a surface have the same viable-non-viable question we have already raised. Everything depends on where you collected the swab or tape sample.

Moving a tape or swab over as little as one inch on a surface, and certainly moving it a few feet, can collect a completely different mold genera and species!

An "expert" should know what's probably representative of the building and should know where the important genera/species are likely to be growing.

Many investigators are quick to sample the highly-visible "black" mold on a surface and under-sample very important but hard to see light colored molds often found higher on a wall, for example, where the surface was less wet.
Cultures are probably not really being done with full accuracy in some labs, especially for Aspergillus: Culturing on one or even two media risks that the important genera/species in the sample does not grow at all on the medium, that it grows in a different form and is identified differently than it appears in the building, or that it is overgrown by another genera/species present which likes the culture more than the target species.

We have demonstrated this culture-media variation in a study we am pursuing about mold in tea. In a problem-tea sample cultured on the most commonly used culture media, MEA, the culture produced an overwhelming growth of Cladosporium sp., while a parallel culture (from the identical sample) made on DG-18 produced a single Cladosporium colony and grew an overwhelming collection of Aspergillus niger!
Non-viable spores, that don't grow on culture may still be toxic or allergenic particles which are a problem for some people exposed to them.

The Penicillium sp. at left was growing nicely in this culture sample, but we have no idea what other molds may have been present but that simply would not grow on this culture media even if they settled on or were placed onto the culture plate.

While we enjoy growing mold cultures in our lab (it makes for nice, photogenic mold colonies), it is less often useful than direct microscopic examination of a field-collected surface or vacuum sample. Without the added step of mold culturing, from a good surface sample using adhesive tape, a trained microscopist can identify mold genera and mold species as well in many cases.

In many instances, knowing the mold genera is enough to decide on a course of cleanup action without further expense. For example, if we agree that there are no harmless Aspergillus species or Penicillium species that grow indoors, then for purposes of deciding on the need for remediation, only the size of the reservoir is important. P. notatum, used for making the drug Penicillin, has not to our knowledge been found growing on building materials.

For more discussion about mold cultures from settlement plates or swabs see "The Validity of Cultures at InspectAPedia.com/sickhouse/cultures.htm

Mold Photos in Petri Dishes - Not so Useful for Environmental Sampling and Mold Identification - What Level of Magnification is Needed to Identify Mold?

Why Can't I Find More Photos of Mold in Petri Dishes?

Question:

I was disappointed as there were no photos at all of petri dish examples of mold, and this is the way most of us out here will be testing for mold. So, how do I explore what mold I have in my petri dish test? I have quarter sized discs of black/dark green mold growing. I did the airborne mold test.

My dog is always coughing and we are in pretty good health but feel a slight "tug" in my breathing, a slight heaviness in my lungs but not bad. I rent my apartment and my landlord has not been responsive to my concerns.

What can I do financially and health wise to explore my situation? Thanks for any tips!!! - Tony K

Reply: Microscopic Examination of Mold is Necessary for Reliable Identification

By Eye Examination of Culture Plates or Petri Dishes to Identify Mold?

The short answer is that you cannot reliably identify what mold is found in a petri dish simply by looking at some photos or color charts. Some mold genera or species might be ruled "out" or "possible" but expert examination of the sample using high-powered microscopy (or another definitive method) is needed. About what you can do about mold, take a look at MOLD EXPERT, WHEN TO HIRE - for help in deciding if your situation honestly merits hiring an expert. Then see MOLD ACTION GUIDE - WHAT TO DO ABOUT MOLD.

We do have some photos of mold in petri dishes posted just above and online, at other of our online articles about the role and limitations of using mold cultures as "home test kits" at Cultures to "Test for Mold". (You'll see there that what grows in culture is not necessarily the dominant or most significant mold that is present in a building.)

Traditionally, petri dish or culture plate photos were included in early mold taxonomy texts, where color and texture of mold growth at that scale assisted in identification of cultures of a known genera down to species level.

These were photos of mold cultured in laboratories where it is sometimes possible to separate a genera of mold (Aspergillus sp.) into species or groups of species (Aspergillus niger) based on color and other macro-characteristics.

In the closeup of a mold culture petri dish growth shown in our photo at above-right, high-powered microscopic examination was necessary to identify Penicillium sp as one of the several mold genera growing among these green, gray,and dark gray colored mold colonies.

Sometimes we can make a pretty good guess about mold identification by the naked eye, if we see a particular color and texture of mold on a particular surface. For example this photo of mold on an orange is showing what is most likely a species of Penicillium. But in general that's not reliable.

Stereoscopic Microscope Photos of Mold to Identify It?

An "in-between" level of magnification, between using the naked eye to look at mold culture growing in a petri dish and using a high powered microscope is the use of a stereo microscope to magnify mold growth on surfaces such as on culture media in a petri dish.

For example, our stereoscopic microscope photo of Fuligo septica (left) is characteristic of that particular fungus.

Stereoscopic mold photos are often beautiful (like this stereoscopic photo of Stemonitis mold growth structures taken in our lab) and may be helpful in identifying a mold genera. Here, for contrast, is a high power microscope photo of Stemonitis mold spores.

But stereoscopic magnification is inadequate for reliable mold identification.

High Powered Microscopic Identification of Mold Spores

For environmental samples in which we need to identify mold genera/species or other particles, it's a different story.

As we operate a forensic lab that processes lots of materials including mold, collected by various means, we see that while petri dish photos are pretty, they are not diagnostic, nor can they be used alone for mold identification at that scale.

We need to examine mold structures and spores at 300x to 1200x to actually identify genera/species reliably. See MOLD BY MICROSCOPE for examples.

The Fuligo septic mold spores in our photo provide very different information than what we can get by eye looking at a mold culture plate or petri dish.

Also see more photos at MOLD ATLAS & PARTICLES INDEX and our Alphabetic Index to Mold Genera or Species

At MOLD "TESTING" vs. MOLD "PROBLEM IDENTIFICATION" we discuss the question of what sorts of mold testing are most useful and which are actually diagnostic, giving information about the presence of a mold problem with enough information that you know what to do about it.

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MOLD TESTING METHOD VALIDITY
  Air samples
    Shortcomings of air sampling
    Mold in Air: Quantitative Analysis
  Tape sampling for mold
    Determination of mold genera
    Determination of mold species
    Shortcomings of tape sampling
  Vacuum samples
    Surface vacuuming
    Shortcomings of surface and carpet vacuuming
    Vacuuming building cavities
    Vacuuming exposed insulation
    Shortcomings of vacuuming insulation
  Cultures to "Test for Mold"
    Shortcomings of culturing
  Swab sampling
  Shortcomings of swab sampling
  PCR methods for Mold Identification
  MOLD TEST vs. PROBLEM DIAGNOSIS
  Are Mold Test Kits Useful?
  Reasons to Test for or Identify Mold
    1. Save Money if it's Just Cosmetic Mold
    2. Mold Related Illness
    3. Mold Cleanup Data baseline

Mark Cramer Inspection Services Mark Cramer, Tampa Florida, Mr. Cramer is a past president of ASHI, the American Society of Home Inspectors and is a Florida home inspector and home inspection educator. (727) 595-4211 mark@BestTampaInspector.com

Thanks to Tony K for discussing mold in petri dishes and indoor sampling or mold testing using cultures - July 2010.

Directories of 6 atlases or indices of building mold

MOLD ATLAS & PARTICLES INDEX - A-to-Z Mold Atlas of Indoor Clinical Mold, Pathogens, Allergens & Other Indoor Particles

MOLD APPEARANCE - WHAT MOLD LOOKS LIKE - What Does Black or Dark Indoor Mold Look Like? Black Mold spores in the Home - a Photo ID Library. What toxic black mold or other indoor mold looks like in buildings.

MOLD GROWTH ON SURFACES, PHOTOS - What Does Mold Look Like on Various Materials & Surfaces? An extensive photographic guide to mold as it is found growing on various building materials & surfaces.

Also see MOLD GROWTH on SURFACES, TABLE OF - a Table of Kinds of Mold Growth Found on Building Surfaces, lists mold genera/species most often found on specific building surfaces, materials, or contents

MOLD in the PETRI DISH, PHOTOS. - Photographs of Mold Growing on Petri Dishes or Mold Culture Plates or Settlement Plates

MOLD BY MICROSCOPE - Mold spores under the Microscope - a Photo ID Library for detection and identification of toxic or other mold

MOLD RELATED ILLNESS SYMPTOMS - Mold Related Illness: Index of Symptoms. Readers should not rely on this document for medical diagnosis and instead should consult with their physician or with a specialist such as a medical toxicologist

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.

Environmental Health & Investigation Bibliography - our technical library on indoor air quality inspection, testing, laboratory procedures, forensic microscopy, etc.

Adkins and Adkins Dictionary of Roman Religion discusses Robigus, the Roman god of crop protection and the legendary progenitor of wheat rust fungus.

Kansas State University, department of plant pathology, extension plant pathology web page on wheat rust fungus: see http://www.oznet.ksu.edu/path-ext/factSheets/Wheat/Wheat%20Leaf%20Rust.asp

"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm

US EPA - Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA

US EPA - Una Breva Guia a Moho - Hongo [Copy on file as /sickhouse/EPA_Moho_Guia_sp.pdf - en Espanol

"A Brief Guide to Mold, Moisture, and Your Home", U.S. Environmental Protection Agency US EPA - includes basic advice for building owners, occupants, and mold cleanup operations. See http://www.epa.gov/mold/moldguide.htm

"Disease Prevention Program for Certain Vegetable Crops," David B. Langston, Jr., Extension Plant Pathologist - Vegetables, University of Georgia (PDF document) original source: www.reeis.usda.gov/web/crisprojectpages/209797.html

"Disease Prevention in Home Vegetable Gardens," Patricia Donald, Department of Plant Microbiology and Pathology, Lewis Jett
Department of Horticulture, University of Missouri Extension - extension.missouri.edu/publications/DisplayPub.aspx?P=G6202

"Management of Powdery Mildew, Leveillula taurica, in Greenhouse Peppers," Ministry of Agriculture and Lands, British Columbia - Original source: www.agf.gov.bc.ca/cropprot/peppermildew.htm

Fifth Kingdom, Bryce Kendrick, ISBN13: 9781585100224, is available from the InspectAPedia online bookstore - we recommend the CD-ROM version of this book. This 3rd/edition is a compact but comprehensive encyclopedia of all things mycological. Every aspect of the fungi, from aflatoxin to zppspores, with an accessible blend of verve and wit. The 24 chapters are filled with up-to-date information of classification, yeast, lichens, spore dispersal, allergies, ecology, genetics, plant pathology, predatory fungi, biological control, mutualistic symbioses with animals and plants, fungi as food, food spoilage and mycotoxins.

Fungi, Identifying Filamentous, A Clinical Laboratory Handbook, Guy St-

US EPA: Mold Remediation in Schools and Commercial Building [Copy on file at /sickhouse/EPA_Mold_Remediation_in_Schools.pdf ] - US EPA

Mycology, Fundamentals of Diagnostic, Fran Fisher, Norma B. Cook, W.B. Saunders Co. 1998, ISBN 0-7216-5006-6 (buy this book at Amazon)

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A Guide to Using Mold Cultures or Settlement Plates to "Test for Mold"

Using Mold Cultures for Home Test Kits for Mold

Mold Cultures are useful for:

Seven Serious Shortcomings of Using Cultures to Test Buildings for the Presence of Toxic Mold

Mold Photos in Petri Dishes - Not so Useful for Environmental Sampling and Mold Identification - What Level of Magnification is Needed to Identify Mold?

Why Can't I Find More Photos of Mold in Petri Dishes?

Question:

Reply: Microscopic Examination of Mold is Necessary for Reliable Identification

By Eye Examination of Culture Plates or Petri Dishes to Identify Mold?

Stereoscopic Microscope Photos of Mold to Identify It?

High Powered Microscopic Identification of Mold Spores

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Directories of 6 atlases or indices of building mold

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair