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  NOTE: May Dooley passed away in March 2024. This site will remain available as a tribute to her.

Using a Microscope for Mold Inspections

Valuable teaching websites for microscope use:

Now that you have your microscope, if you haven’t already looked at How to Use the Microscope to learn the parts of a microscope and how to operate it, do so now. We'll be reviewing some of this below as we apply the information to our task, but it would be good for you to get the overview first. That page is from The Biology Corner, a website for science teachers.

In the Tape Testing for Mold topic, we’ll be talking about how and where to tape sample, but meanwhile, let’s get the background work done for looking at a slide under the microscope.

Setting up a microscope slide

Focusing the microscope

Focus the eyepieces to your eyes

Other knobs

Practice with your microscope

I trained myself to look at and identify mold. You can do the same. I worked with the book, Identifying Filamentous Fungi – A Clinical Laboratory Handbook, by Guy St-Germain and Richard Summerbell, Star Publishing Company, CA, 650-591-3505.

Let me know how I can help. Perhaps you would like to send me photos of what you are seeing under the microscope to confirm the identification. Check the master list of photos in the next section.

Gather your supplies:

Stain your sample.

Don’t spill the bottle of stain!

Taking tape samples

What you should have now is a 3” piece of tape that has nothing but fingerprints on the ends and some debris in the center of the tape. Even a half inch or less of debris is fine, less than the size of a dime. When the debris is magnified 400 or 600 times, the area could look as big as a football field.

Now that you have your tape sample, you’re ready to stain the sample.

Now that we’ve gone through preparing a single sample, let’s back up a minute and talk about how to take multiple samples and not mix them up. Here’s my method:

At the microscope

Here’s some help with focusing the microscope:

At 600x, you’ll be able to see mold. If you know what to look for, you’ll find it sooner or later. Let me share my early experience with you.

May as a beginner with the microscope

I had had some background biology and microbiology science classes in college and grad school, and more when I started environmental home inspection studies, beginning in 1994. Those were the days before mold became a hot topic, and not much class time was devoted to the subject of mold inside houses.

Around 1996, I found a reference book mentioned above which would become my classroom. Identifying Filamentous Fungi: A Clinical Laboratory Handbook, by Guy St-Germain and Richard Summerbell, can be ordered from Star Publishing Company, 1-650-591-3505 (though they have an newer book out since then). There are pictures and descriptions of what mold looks like under the microscope, so you can match what you’re seeing with the pictures. The book gives several ways of identifying mold, and I spent hours and hours with that book and use it to this day as a reference. Your progress will be much faster, because I am going to tell you some shortcuts. You’d enjoy the book, but you’ll find enough here to get you started.

The first mold I identified microscopically was green bread mold, Penicillium. I was able to focus in and see the chains of spherical spores easily. I knew that I needed to find a fruiting body that produces the spores to be sure I was seeing Penicillium. There were so many spores on the slide I was viewing that I couldn’t see fruiting bodies for quite a while. Finally, I figured I’d look around the edges of the mold, where the growth wasn’t so dense. Suddenly, I saw a branch-like fruiting body with chains of spores coming off the tips. How exciting! How delicate, how beautiful! My first positive identification! I was on the way.

Since those days, I have identified a lot of the molds in the St-Germain-Summerbell book. When I started, I’d see a new mold and then leaf through the book to see if I could identify the mold. I’d look for the fruiting bodies, for the shapes of the spores, for the colors of the colonies (if I was growing them), and for other identifying characteristics that the book listed. How exciting to see Trichoderma, Mucor, Rhizopus, Syncephalastrum, right under my microscope! And to find other molds, one after the other. Some of these molds have to be grown in Petri dishes from air samples; you typically won’t find them on tape samples.

The good news is that there are only about a half dozen common indoor molds associated with dampness conditions. Thus, while I had a lot of gratification from learning to identify other molds, most of what I saw at houses was Alternaria, Aspergillus, Aureobasidium, Chaetomium, Cladosporium, Penicillium, Stachybotrys, and sometimes Trichoderma.

These common indoor molds can be found through tape sampling. Unless you decide to do culture plate air sampling business, you probably won’t find too many fungi beyond these.

Some molds are not in my reference book. The St-Germain-Summerbell book deals just with molds that are known to affect human health, particularly through infection. Allergic or asthmatic symptoms or neurological concerns are not addressed in the book. So the book is limited, but it’s a good place to start for the pictures and descriptions. An Internet search on various molds brings up an endless list of sites relating to mold and to specific kinds of mold. Include “microscope picture” and the name of the mold in your search terms, and you’ll be in business.

Many molds don’t produce spores, and all you see under the microscope is a bunch of branches. These may be “sterile fungi” or “non-sporulating fungi,” which may or may not be allergenic. Little is known about them, and there are many, many species, often with minor variations. Labs generally don’t further differentiate them, if they are listed at all. As with any mold, clean off surface growth and try to prevent re-growth. One microbiology professor called them “the white fuzzies.”

The field of mycology (a branch of botany dealing with fungi) is vast. One day I read about a book identifying molds growing on telephone poles. Checking out telephone pole fungi sounded like a fun thing to do, so I ordered a copy of the book. Forget it. Trying to get conversant with the tiny distinguishing aspects of 1000 similar-looking molds was definitely not fun. I’ll leave telephone poles to the microbiologists. Nor do I try to distinguish among even the common species of common molds, such as Aspergillus. I leave that up to the microbiologists, should a client need to know. Sometimes the report comes back listing some species that aren’t even in my reference books. There are whole books written just on Aspergillus species. There’s also a website, www.aspergillus.org.uk.

Using immersion oil to get higher magnification

Skip this section if you’re not planning to work with 1500x magnification (the 100x objective x 15x eyepiece). I seldom use 1500x, but since many microscopes will come with a 100x objective, I’m including basic information on how to use it.

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Next up: my cheat sheet of Mold under a Microscope or back to the Mold Topic Index.

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