Mold identification

Mold identification

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I poured some agar plates and tried inoculating them with mushroom spores (I don't think they germinated bc of low humidity), but noticed what looks like mold with crystals on the surface of the agar.

My question is, what are these "dew-like" structures?

Location: Near Columbus, Georgia

Incubation conditions: Indoors (room temp), covered

I initially figured it was condensation from the agar. But it is not on your lid and you said you suspected humidity was low.

I found this here with this caption

Mold, Penicillium vermiculatum, growing on agar. The water droplets on the mold are part of the respiration process of the mold.

Those droplets do look like pure water. And oxidative metabolism does produce water:
CHOH+O2 -> CO2 + H2O. It is interesting that the top of the mold is so hydrophobic that the water forms little balls. Why might that be? If you know, comment please.

Other fungi might put stuff in the exudates that collect atop them. I read that some aspergillum species collect droplets of purple exudate on old colonies but I could not find good images. Here is another penicillium with amber looking exudate. These exudates can contain metabolic products.


Exudates (or Extrolites): Some fungi can produce exudates as a by-product of their growth, many of which can be collected for commercial use. Mycotoxins are by-products (secondary metabolites) which are potent poisons. Penicillium citrinum produces Citrinin, a nephrotoxic mycotoxin which derives its name from the fungus. It may also produce other extrolites such as tanzowaic acid A, quinolactacins, quinocitrinines, asteric acid and compactin.

If these fungi were spreading out in their natural habitat of rotten stuff, the secreted mycotoxins would be clearing a path for them, wiping out those organisms that dare compete for that rotten stuff.

Lab 10: Fungi, Part 2 - The Molds

Molds are multinucleated, filamentous fungi composed of hyphae. A hypha is a branching, tubular structure from 2-10 µm in diameter and is usually divided into cell-like units by crosswalls called septa. The total mass of hyphae is termed a mycelium. The portion of the mycelium that anchors the mold and absorbs nutrients is called the vegetative mycelium the portion that produces asexual reproductive spores is termed the aerial mycelium (see Figure 1) .

Molds possess a rigid polysaccharide cell wall composed mostly of chitin and, like all fungi, are eukaryotic (see Figure 2). Molds reproduce primarily by means of asexual reproductive spores such as conidiospores, sporangiospores, and arthrospores. These spores are disseminated by air, water, animals or objects and upon landing on a suitable environment, germinate and produce new hyphae (see Figure 1). Molds may also reproduce by means of sexual spores such as ascospores and zygospores, but this is not common. The form and manner in which the spores are produced, along with the appearance of the hyphae and mycelium, provide the main criteria for identifying and classifying molds.


  • Scanning electron micrograph of the conidiospores of Penicillium courtesy of Dennis Kunkel's Microscopy .
  • Scanning electron micrograph of the conidiospores of Aspergillus courtesy of Dennis Kunkel's Microscopy .

Although generally harmless in most healthy individuals, Aspergillus species do cause allergic bronchopulmonary aspergillosis (ABPA), chronic necrotizing Aspergillus pneumonia (or chronic necrotizing pulmonary aspergillosis [CNPA]), aspergilloma (a mycetoma or fungus ball in a body cavity such as the lung), and invasive aspergillosis. In highly immunosuppressed individuals, however, Aspergillus may disseminate beyond the lung via the blood.

Rhizopus is an example of a mold that produces sporangiospores. Although usually nonpathogenic, it sometimes causes opportunistic wound and respiratory infections in the compromised host. At the end of its sporangiophore is dome-shaped end called a columella that extends into a sac-like structure called a sporangium. Its sporangiospores, typically brown or black, are produced within the sporangium (see Figure 7). Anchoring structures called rhizoids are also produced on the vegetative hyphae.

Mucormycoses are infestions caused by fungi belonging to the order of Mucorales. Rhizopus species are the most common causative organisms. The most common infection is a severe infection of the facial sinuses, which may extend into the brain. Other mycoses include pulmonary, cutaneous, and gastrointestinal.

Rhizopus can also reproduce sexually. During sexual reproduction (see Figure 8), hyphal tips of (+) and (-) mating type join together and their nuclei fuse to form a sexual spore called a zygospore (see Figure 9). This gives rise to a new sporangium producing sporangiospores having DNA that is a recombination of the two parent strain's DNA.

Molds are commonly cultured on fungal-selective or enriched media such as Saboraud Dextrose agar (SDA), Corn Meal agar, and Potato Dextrose agar.


The dermatophytes are a group of molds that cause superficial mycoses of the hair, skin, and nails and utilize the protein keratin, that is found in hair, skin, and nails, as a nitrogen and energy source. Infections are commonly referred to as ringworm or tinea infections and include:

  • tinea capitis (infection of the skin of the scalp, eyebrows, and eyelashes)
  • tinea barbae (infection of the bearded areas of the face and neck)
  • tinea faciei (infection of the skin of the face)
  • tinea corporis (infection of the skin regions other than the scalp, groin, palms, and soles)
  • tinea cruris (infection of the groin jock itch)
  • tinea unguium (onchomycosis infection of the fingernails and toenails)
  • tinea pedis (athlete's foot infection of the soles of the feet and between the toes).

The three common dermatophytes are Microsporum, Trichophyton, and Epidermophyton. These organisms grow well at 25°C. They may produce large leaf or club-shaped asexual spores called macroconidia (see Figure 10B) as well as small spherical asexual spores called microconidia, both from vegetative hyphae (see Figure 10A).

Microsporum commonly infects the skin and hair, Epidermophyton, the skin and nails, and Trichophyton, the hair, skin, and nails. Dermatophytic infections are acquired by contact with fungal spores from infected humans, animals, or objects. On the skin, the dermatophytes typically cause reddening, itching, edema, and necrosis of tissue. This is a result of fungal growth and a hypersensitivity of the host to the fungus and its products. Frequently there is secondary bacterial or Candida invasion of the traumatized tissue.

To diagnose dermatophytic infections, tissue scrapings can be digested with 10% potassium hydroxide (which causes lysis of the human cells but not the fungus) and examined microscopically for the presence of fungal hyphae and spores. To establish the specific cause of the infection, fungi from the affected tissue can be cultured on Dermatophyte Test Medium (DTM) and Saboraud Dextrose agar (SDA).

Dermatophyte Test Medium (DTM) has phenol red as a pH indicator with the medium yellow (acid) prior to inoculation. As the dermatophytes utilize the keratin in the medium, they produce alkaline end products that raise the pH, thus turning the phenol red in the medium from yellow or acid to red or alkaline (see Figure 17).

The types of macroconidia and microconidia (see Figure 10B) can be observed by growing the mold on SDA and observing under a microscope. In addition, many dermatophyte species produce yellow to red-pigmented colonies on SDA and the most common species of Microsporum fluoresce under ultraviolet light.


Dimorphic fungi may exhibit two different growth forms. Outside the body they grow as a mold, producing hyphae and asexual reproductive spores, but inside the body they grow as a yeast-like form. Dimorphic fungi may cause systemic mycoses which usually begin by inhaling spores from the mold form. After germination in the lungs, the fungus grows as a yeast. Factors such as body temperature, osmotic stress, oxidative stress, and certain human hormones activate a dimorphism-regulating histidine kinase enzyme in dimorphic molds, causing them to switch from their avirulent mold form to their more virulent yeast form.

The infection usually remains localized in the lungs and characteristic lesions called granuloma may be formed in order to wall-off and localize the organism. In rare cases, usually in an immunosuppressed host, the organism may disseminate to other areas of the body and be life threatening. Examples of dimorphic fungi include Coccidioides immitis, Histoplasma capsulatum, and Blastomyces dermatitidis.

1. Coccidioides immitis

Coccidioides immitis (see Figure 11) is a dimorphic fungus that causes coccidioidomycosis, a disease endemic to the southwestern United States. An estimated 100,000 infections occur annually in the United States, but one to two thirds of these cases are subclinical. The mold form of the fungus grows in arid soil and produces thick-walled, barrel-shaped asexual spores called arthrospores by a fragmentation of its vegetative hyphae (see Figure 13 and Figure 17).

After inhalation, the arthrospores germinate and develop into endosporulating spherules in the terminal bronchioles of the lungs (see Figure 14A and 14B). The spherules reproduce by a process called endosporulation, where the spherule produces numerous endospores (yeast-like particles), ruptures, and releases viable endospores that develop into new spherules.

Coccidioidomycosis can be diagnosed by culture, by a coccidioidin skin test, and by indirect serologic tests (discussed in Lab 18).

2. Histoplasma capsulatum

Histoplasma capsulatum(see Figure 12) is a dimorphic fungus that causes histoplasmosis, a disease commonly found in the Great Lakes region and the Mississippi and Ohio River valleys. Approximately 250,000 people are thought to be infected annually in the US, but clinical symptoms of histoplasmosis occur in less than 5% of the population. Most individuals with histoplasmosis are asymptomatic. Those who develop clinical symptoms are typically either immunocompromised or are exposed to a large quantity of fungal spores.

The mold form of the fungus often grows in bird or bat droppings or soil contaminated with these droppings and produces large tuberculate macroconidia and small microconidia (see Figure 15). Although birds cannot be infected by the fungus and do not transmit the disease, bird excretions contaminate the soil and enrich it for mycelial growth. Bats, however, can become infected and transmit histoplasmosis through their droppings. After inhalation of the fungal spores and their germination in the lungs, the fungus grows as a budding, encapsulated yeast (see Figure 16).

Histoplasmosis can be diagnosed by culture, by a histoplasmin skin test, and by indirect serologic tests (discussed in Lab 18).

3. Blastomyces dermatitidis

Blastomycosis, caused by Blastomyces dermatitidis, is common around the Great Lakes region and the Mississippi and Ohio River valleys.Infection can range from an asymptomatic, self-healing pulmonary infection to widely disseminated and potentially fatal disease. Pulmonary infection may be asymptomatic in nearly 50% of patients. Blastomyces dermatitidis can also sometimes infect the skin.

Blastomyces dermatitidis produces a mycelium with small conidiospores and grows actively in bird droppings and contaminated soil. When spores are inhaled or enter breaks in the skin, they germinate and the fungus grows as a yeast having a characteristic thick cell wall. It is diagnosed by culture and by biopsy examination.

For a decription of antifungal agents used to treat fungal infections, see section IIE: Chemotherapeutic Control of Fungi in you lecture E-text.

Observe Mold Up Close

To examine mold under the microscope, it is best to grow your own in a controlled environment. We recommend using soft bread that is preservative-free, but many fruits or vegetables such as potatoes or oranges will also work. A good sample of mold may take up to two weeks to form, so be sure to plan ahead for this project. Please note: we do not recommend this project for those with allergies to mold (including penicillin) or with severe asthma.

The easiest way to grow mold is on a piece of bread. Any preservative-free bread that is soft will work well. Bread with preservatives in it will take much longer to form mold. Leave the bread in the open for about an hour so it is exposed to contaminants in the air. Place the bread in a ziplock bag, and sprinkle water over it so it is damp. Seal the bag, leaving some air inside. Place the bag in a dark, warm place, away from other food items. A kitchen cupboard close to the stove may be one option. Or you could place it next to a window, with a bowl or plate covering it from the light. Mold will grow best in a moist environment. Mold should start forming in 2-3 days, but will take a week or more to get a good sample.

Check on the piece of bread every few days, and add more water if it is becoming dried out. Avoid opening the plastic bag as much as you can. If you touch the bread, be sure to thoroughly wash your hands afterwards. When sufficient mold has formed, you can prepare a slide and examine it under the microscope (student microscopes work well for this). You will need a sample that is about one inch across.

What You Need:

Safety Note: When handling mold, it is very important to cover as much skin as you can, and to wear gloves. Mold is an allergen and can be toxic. Working with mold as you are in the experiment typically only affects the very young or very old, or those with severe immune problems, but it is important to take precautionary measures (such as gloves) and to not do this project if you have allergies or asthma.

What You Do:

  1. Place a drop of water in the center of the slide, using an eyedropper if you have one, or the tip of a clean finger. You can use solution of methylene blue instead, which is a microscope stain, and makes the sample easier to see by coloring certain parts of the mold cells.
  2. Using a toothpick, scrape some of the mold off, and place it on the drop of water.
  3. Take the cover slip and set it at an angle to the slide so that one edge of it touches the water drop, then carefully lower it over the drop so that the cover slip covers the specimen without trapping air bubbles underneath.
  4. Use the corner of a paper towel to blot up any excess water at the edges of the cover slip.
  5. View the slide with a compound microscope, starting with a low objective.

Did you know molds are actually fungi? Fungi are found in all sorts of environments, and some are helpful, while others can be harmful. Mushrooms are actually a type of edible fungi. Mold is certainly a nuisance on food, but some antibiotics have been made from mold similar to the kind you grew.

The colorful growth on the bread is made of connected thread structures called hyphae. These form a mold colony which was started by a single mold spore. The hyphae may look soft and fuzzy, or it could be very colorful. By looking at the hyphae under a microscope, you will be able to identify what kind of mold it is.

Rhizopus feeds on starch or sugar, making it a common mold on bread. This type of mold may start off as white hair-like structures and eventually will form solid black spots. Under the microscope, Rhizopus appears as short strands with oval-shaped heads, looking like a balloon on a string. The head is where the spores of this type of mold are contained.

Aspergillus is another mold commonly found on food items, especially grains. It is a typically a bluish green color, with a thin ring of white around each colony. Some species of Aspergillus are black in color. You can identify this type of mold by making a slide and viewing it under the microscope. It has a thin branch-like structure, with heads that look like blooming flowers, and release spherical spores.

Penicillium, which is where the powerful antibiotic Penicillin comes from, can be blue-green or gray, often with a fuzzy white edge. This type of mold is common, and often looks like Aspergillus with the naked eye. If you examine it under a microscope, you will see that the head has thinner structure than Aspergillus, with several strand segments branching out from the main strand. At the end of each segment of the head you should be able to see small spores.

Clean-up: When the experiment is finished, put the bread and anything that touched it (including the gloves and apron) in a heavy-duty plastic zip lock bag, and throw it away. The slide will not be permanent, and should be disposed of as well. Clean the area you were working in thoroughly with bleach wipes (such as Clorox) or soap and water.

Mold needs nourishment. Mold obtains that nourishment by growing on organic matter.

Mold requires only a small amount of organic matter to live. Mold ingests that organic matter very slowly.

An example of mold utilizing organic matter for its nourishment is found on food items that “have gone bad.” You may see a small amount of mold initially. Over time, the mold on a food item increases. A considerable amount of time can pass before the mold completely “ingests” a particular food item.

General Information about Mold

Mold can cause many health effects. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash. People with asthma or who are allergic to mold may have severe reactions. Immune-compromised people and people with chronic lung disease may get infections in their lungs from mold.

There is always some mold around. Molds have been on the Earth for millions of years. Mold can get in your home through open doors, windows, vents, and heating and air conditioning systems. Mold in the air outside can be brought indoors on clothing, shoes, bags, and even pets.

Mold will grow where there is moisture, such as around leaks in roofs, windows, or pipes, or where there has been a flood. Mold grows on paper, cardboard, ceiling tiles, and wood. Mold can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery.

Basic Facts about Mold [Español]
FAQs about molds, where they are found, how to eliminate them, and how they can affect people&rsquos health&hellip more

Learn about Mold

  • about state and local laws that apply to IAQ conditions in rental properties. Visit Environmental Law Institute’s Indoor Air Quality in Rental Dwellings and Indoor Air Quality Guide for Tenants. Exit
  • National Institute of Occupational Safety and Health recently released Dampness and Mold Assessment Tool for Schools and General Buildings.
  • ducts have been recalled for mold problems. Check, the Publicly Available Consumer Product Safety Information Database website of the U.S. Consumer Product Safety Commission (CPSC).

Morphological Characteristics of Fungi | Microbiology

The slime-molds are morphologically distinct from other fungi in having a body consisting of either cell wall-less amoebae (cellular slime molds e.g. Dictyostelium) or a mass of multinucleate protoplasm in which individual cells are indistinguishable (acellular slime molds e.g. Stemonitis, Ceratomyxa etc.). Other fungi have either single cells e.g. yeasts, chytrids etc., or mycelia.

Unicellular forms may be motile or non-motile. Mycelial fungi can have septate or aseptate hyphae. In unicellular and hyphal fungi, the cell is externally bound by a firm but elastic cell wall composed of micro fibrils of cellulose, chitin or other polymeric compounds. The micro fibrils are embedded in a matrix of proteins, lipids and other substances. Chitin is a characteristic component of the cell wall of most higher fungi. It is a polymer of N-acetyl glucosamine in which the monomers are linked to each other by 1, 4-β- glycosidic bonds (Fig. 5.1). Interestingly, chitin is also present in arthropods.

The protoplast of fungal cells is typically eukaryotic containing membrane-bound nucleus and other cell organelles, like mitochondria, rough and smooth endoplasmic reticulum, microtubules, Golgi bodies etc. Ribosomes are of 80S type. Vacuoles are often present occupying the major part of the cells, pushing the cytoplasm to the periphery. Cytoplasmic streaming is also observed. As reserve material, fungi generally accumulate glycogen which is a branched polymer of glucose. Fats and oils are also often present.

In the majority of fungi, the vegetative body is made of hyphae. A hypha generally originates by germination of a spore which may be produced by asexual or sexual means. The germ-tube of a germinating spore elongates into a hypha which grows at or near the tip.

Hyphae of lower fungi, like water-molds and oomycetes are broader, non-septate, multinucleate and coenocytic in vegetative stage. In contrast, hyphae of higher fungi—like ascomycetes and basidiomycetes—are less broad, septate and contain generally one or two nuclei per cell.

The septum arises by centripetal growth of the hyphal wall, but the inward growth of the septum remains incomplete leaving one or, sometimes, more than one gap, called a pore through which contact between the two adjacent cells is maintained.

Sometimes, individual hyphae grow intertwined with each other to form a more or less compact tissue, called plectenchyma. When, in such a tissue, the individual hyphae are recognizable, it is known as prosenchyma. On the other hand, the tissue is called a pseudo-parenchyma when the individual hyphae lose their identity.

In some fungi, the pseudo-parenchymatous tissue may form a small tuber­-like structure, called a sclerotium. Sclerotia may be spherical, as in Sclerotium rolfsii or an elongated structure, as in Claviceps purpurea. In some fungi, the hyphal tissue may form an elongated, branched root-like structure, known as a rhizomorph, as in Armillaria mellea. Generally, the complex hyphal tissues are found in higher fungi. Some morphological features of fungi are depicted in Fig. 5.2.

Mold identification - Biology

Mold can cause many health effects. For some people, mold can cause a stuffy nose, sore throat, coughing or wheezing, burning eyes, or skin rash. People with asthma or who are allergic to mold may have severe reactions. Immune-compromised people and people with chronic lung disease may get infections in their lungs from mold.

There is always some mold around. Molds have been on the Earth for millions of years. Mold can get in your home through open doors, windows, vents, and heating and air conditioning systems. Mold in the air outside can be brought indoors on clothing, shoes, bags, and even pets.

Mold will grow where there is moisture, such as around leaks in roofs, windows, or pipes, or where there has been a flood. Mold grows on paper, cardboard, ceiling tiles, and wood. Mold can also grow in dust, paints, wallpaper, insulation, drywall, carpet, fabric, and upholstery.

Difference Between Mold and Yeast

Hi, I am a medical physicist with experience in radiation protection. EM radiation does not cause yeast overgrowth. It does cause some heating if strong enough and so could contribute to creating a warm moist environment beneficial to yeast, but the strength from a phone mast 30m away would be way too low to do this. Your other sources of heat in the room would be much greater (including the heat you yourselves give out). Jeremy mentioned CRT devices (old style televisions). As well as supplying heat these are in a vented enclosed box which is never cleaned out (the TV case) so they accumulate all manner of airborne nutrients such as dust (mostly dead skin) and so could very well provide a great environment for microbial growth , particularly if the room is damp. If I had the problem you describe I would be thinking of buying a dehumidifier and increase the vacuuming dusting polishing routine. If the room is not humid then the problem is more of a medical one (ie in your body and not to do with your bedroom).

Thanks for your clear answer. Can I ask you another question? Can Electro Magnetic Fields cause Candidiasis (yeast overgrowth). Our bedroom was 30 meters from a cell tower for approximately six years. It caused a number of symptoms which we were able to positively identify with wireless radiation. Later, after following an anti-candida diet for a few weeks, we had the same symptoms that we had from the EMF. Have you ever heard that wireless radiation can cause candida to overgrow? Thanks for your time.

Hello Lydia, I’m a PhD in Mycology and I can help you with that. While you are on the right track with that thinking, my research has found that cell tower radiation does nothing related to said overgrowth, however we have found out that the dissipate electromagnetic energy from televisions and most current generation screens does cause this overgrowth you speak of, perhaps you have a television in the house that’s regularly used – or maybe a neighbor of yours has a old CRT one, as we also discovered that the radiation from these has a stronger, more lingering effect than current generation ones.

Plasmodial Slime Molds

Plasmodial slime molds represent a vast diversity of morphologies. While still a plasmodium (see Figure (PageIndex<5>)), they can be difficult to distinguish. However, once they have formed into a fruiting structure, they can form distinct, varied, and amazing shapes (see Figure (PageIndex<6-9>))!

The Plasmodium

Figure (PageIndex<5>): This image shows Physarum polycephalum exploring some decaying wood. This is the feeding plasmodium. During this stage, the giant, multinucleate amoeba moves over the substrate engulfing bacteria. The veins allow for streaming of the cytoplasm and efficient connections between sources of food. Photo by Daniel Folds, CC BY-NC.

Sporocarp Diversity

Figure (PageIndex<6>): Hemitrichia serpula forms an uncommon fruiting body called a plasmodiocarp. The feeding stage accumulates its protoplasm into the veins of the plasmodium, forming strange linear, intertwining shapes. Photo by Roman Providukhin, CC-BY-NC. Figure (PageIndex<7>): Fruiting bodies of the plasmodial slime mold Lycogala epidendrum form into cushion-like structures called aethalia. The plasmodium has formed into pink ball-like structures on the surface of a rotten log. One of these structures has been popped and is oozing a pink slime, full of immature spores. This pink slime gives Lycogala its name, wolf's milk. Photo by Maria Morrow, CC BY-NC. Figure (PageIndex<8>): Another option for a fruiting structure is the pseudoaethalium, where there are distinct sporangia but they still form together like a cushion. This is the type of fruiting structure formed by Tubifera ferruginosa, the red raspberry slime mold. Photo by Hiromi Karagiannis, CC BY-NC. Figure (PageIndex<9>): Fruiting bodies of Diachea leucopodia have a distinct stalk and sporangium. The stalk in this species is white, while the elongate sporangium displays an oil-sheen rainbow of colors. Photo by Sypster, CC BY-NC.

Other Features

Figure (PageIndex<10>): This fruiting body of Arcyria denudata shows an interesting feature of slime mold anatomy. The sporangium is composed of a peridium (skin) that encloses the spores. The spores are often intermixed with a tangle of filaments called the capillitium, which helps disperse the spores. In this image, the pink capillitium (full of spores) can be seen bursting out of the sporangium. Photo by Alexander Shirokikh, CC BY-NC.

In addition to having interesting macroscopic morphologies, they also have interesting microscopic features! Ornamentation and size of the spores, as well as the appearance of the capillitial threads, can be necessary for identification.

Watch the video: Why Mold Is So Hard To Kill (October 2022).