1. Mycology Opportunistic Molds
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Mycology Opportunistic Molds
Hi I’m Carol Larson, your guide thru this tutorial about the opportunistic molds. This lesson will be of value to you as you rotate thru the Mycology unit during 2nd semester. You will find an audio icon on each screen of this presentation. Please click on the icon to hear my narration for that specific screen. You may also follow along with the lecture handout entitled “Opportunistic Molds” that you can print out from this blackboard lesson.
Division of Medical Technology
Carol Larson MSEd, MT(ASCP)

2. Basic Characteristics
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Basic Characteristics
Rapid growers (4-5 days)
Found in soil (saprobic)
Conidia are airborne
Opportunistic pathogens
Treatment
The opportunistic molds are rapid growers; meaning their colonies are mature at 4-5 days. These molds are normally found in soil and referred to as saprobic. Their conidia are airborne.
Clinically, when given opportunity, these molds can be opportunistic pathogens. The route of infection is usually by inhalation of the conidia. The infection is dependent upon what the body does after inhalation. Immunocompromised patients are easily susceptible to these opportunistic molds. Treatment can be very toxic. Thus it is important to determine if the isolate is a laboratory contaminant or the actual cause of the patient’s disease. Examination of the patient’s tissue, or the same isolate from more than one body site aids in determining pathogenicity.

3. Opportunistic Mold Classification
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Opportunistic Mold Classification
Aseptate (sparsely septate) / hyaline
Septate / dematiaceous
Septate / hyaline
When it comes to identifying the opportunistic molds, we start by looking at the key characteristics of the hyphae. As you will recall from the Introductory Mycology lecture that you received the last day of student lab, we briefly discussed there are 2 ways to classify the hyphae of mold – by the presence or absence of septa, and by the color of the hyphae. The opportunistic molds have three general categories of classification: aseptate (or sparsely septate) hyphae that are hyaline (or light) color, septate hyphae that are dematiaceous (or dark) color, and septate hyphae that are hyaline color.

4. Zygomycetes Lid lifters Sporangiospores Rhizoids
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Aseptate (sparsely septate) hyaline hyphae
Zygomycetes
Lid lifters
Sporangiospores
Rhizoids
Lets begin with the aseptate hyaline hyphae. This group of molds are known as the Zygomycetes. Key characteristics for identification include colony morphology in that they are lid lifters. Within a couple of days, the aerial mycelium will grow so high that it can actually lift the culture plate lid off of the plate if not secured. The mycelium is describes as being very cottony. Microscopically, besides evaluating the appearance of the hyphae, you will look for the characteristic asexual reproductive structures know as sporangiospores. In addition, the presence or absence of rhizoids (or root-like structures) are determined.

5. Clinical Significance
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Aseptate (sparsely septate) hyaline hyphae
Clinical Significance
Causes Zygomycosis (Mucormycosis, Phycomycosis)
Predisposition
Diabetics
Malnutrition
Immunosuppressed
Prolonged antibiotic therapy
Pathogenesis
Nasal sinuses
Migrate to brain and meninges
The Zygomycetes cause Zygomycosis (also known as Mucormycosis or Phycomycosis). Patients who have a predisposition to getting this disease include diabetics, malnourished, immunosuppressed (AIDS), and prolonged antibiotic therapy (which decreases normal flora). The pathogenesis for this disease begins with the inhalation of spores. Infection begins in the nasal sinuses causing the nasal discharge to be black. The mold then Spreads to adjacent blood vessels and causes necrosis and vascular thrombosis (blood clots). The mold can migrate to the brain and meninges which can lead to a rapidly fatal meningoencephalitis (usually 2-10 days after infection).

6. Absidia species Internodal rhizoids
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Aseptate (sparsely septate) hyaline hyphae
Absidia species
Internodal rhizoids
There are three Zygomycetes that we will look at. The first one is Absidia species. The key characteristic for identification of Absidia is the presence of internodal rhizoids (root-like hyphae spaced between the bases of the sporangiophores).

7. Mucor species No rhizoids Aseptate (sparsely septate) hyaline hyphae
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Aseptate (sparsely septate) hyaline hyphae
Mucor species
No rhizoids
The second Zygomycete of interest is Mucor species. Its key characteristic for identification is the absence of rhizoids.

8. Rhizopus species Nodal rhizoids
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Aseptate (sparsely septate) hyaline hyphae
Rhizopus species
Nodal rhizoids
And the last Zygomycete we will focus on is Rhizopus species. Its key identification characteristic is the presence of nodal rhizoids located at the base of the sporangiophore.

9. In Review … Aseptate (sparsely septate) hyaline hyphae Zygomycetes
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Aseptate (sparsely septate) hyaline hyphae
In Review …
Aseptate (sparsely septate) hyaline hyphae
Zygomycetes
Lid lifters, sporangiospores
Absidia – internodal rhizoids
Mucor – no rhizoids
Rhizopus – nodal rhizoids
Zygomycosis
So in review, the aseptate or sparsely septate hyaline hyphae opportunistic molds are the Zygomycetes. They are rapid growers, lid lifters, and produce sporangiospores. The three genus’ of interest include Absidia with internodal rhizoids, Mucor with no rhizoids, and Rhizopus with nodal rhizoids. They all are able to cause Zygomycosis, an opportunistic infection of the nasal passages especially in diabetics and immunocompromised patients.

10. Opportunistic Mold Classification
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Opportunistic Mold Classification
Aseptate (sparsely septate) / hyaline
Septate / dematiaceous
Septate / hyaline
Now we are going to take a look at the Septate hyphae opportunistic molds. They are subdivided into dematiaceous and hyaline groups. The dematiaceous opportunistic molds will have hyphae and conidia that are dark brown in color.

11. Alternaria species Colony morphology: Microscopic morphology:
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Septate / dematiaceous hyphae
Alternaria species
Colony morphology:
Microscopic morphology:
Alternaria’s colony morphology is a Pale gray to olive brown surface, with a brown to black reverse. The texture of the colony is downy to wooly. Microscopically the hyphae are segmented, brown in color and have poroconidia that contain horizontal and vertical septa with club-shaped bases and tapered ends. You can easily see how it got its name.

12. Cladosporium species Colony morphology: Microscopic morphology:
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Septate / dematiaceous hyphae
Cladosporium species
Colony morphology:
Microscopic morphology:
Cladosporium’s colony morphology is an olive brown to brownish-black surface and reverse, and the texture is velvety. Microscopically the hyphae are segmented, brown in color and have short chains of long, thin, oblong blastoconidia that appear to be branching. You will also often times see shield-shaped spores with scars at points of attachment.
The opportunistic Cladosporium species grow best at 30ºC and are rapid growers. There is also a pathogenic Cladosporium species that grows best at 35ºC and is a slower grower. We will discuss this mold in another lesson relating to the subcutaneous molds.
Cladosporium species may be confused with Paecilomyces species who’s blastoconidia do not branch and have hyaline hyphae.

13. In Review … Septate, dematiaceous hyphae Alternaria species
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Septate / dematiaceous hyphae
In Review …
Septate, dematiaceous hyphae
Alternaria species
Cladosporium species
Generally nonpathogenic
So in review, the septate dematiaceous hyphae opportunistic molds are are generally considered nonpathogenic. They are rapid growers and are identified by their colony morphology and microscopic morphology. The two genus’ of interest include Alternaria and Cladosporium.

14. Opportunistic Mold Classification
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Opportunistic Mold Classification
Aseptate (sparsely septate) / hyaline
Septate / dematiaceous
Septate / hyaline
The last classification group we are going to take a look at are the hyaline septate hyphae opportunistic molds. These molds, just like the dematiaceous septate hyphae molds, are considered nonpathogenic with a few exceptions that we will discuss.

15. Aspergillus species Causes Aspergillosis Predisposed Pathogenesis
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Septate / hyaline hyphae
Aspergillus species
Causes Aspergillosis
Predisposed
Debilitated & immunocompromised
Pathogenesis
Inhale conidia
Pulmonary disease
Systemic
Aspergillus species is the first mold we will look at in the category of septate hyaline hyphae opportunistic molds. It can cause Aspergillosis. Those who are predisposed to this disease include debilitated and immunocompromised patients. The pathogenesis involves the inhalation of conidia and the development of a pulmonary disease. It can also invade the surrounding blood vessels and become systemic. It is very invasive and has a rapid process for spreading. Some of the clinical diseases seen with Aspergillus include: asthma, farmer’s lung (a chronic pulmonary problem), burn infections, and mycotic keratitis (an infection of the cornea).

16. Aspergillus fumigatus
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Septate / hyaline hyphae
Aspergillus fumigatus
Colony morphology:
Microscopic morphology:
There are over 200 Aspergillus species, but we are going to focus only on three of them. The first one is Aspergillus fumigatus. To identify the Aspergillus species, we look at the colony morphology and the arrangement of phialoconidia on the phialids and vesicle to speciate. Aspergillus fumigatus is the most common pathogenic Aspergillus species. Its colony morphology is initially white in color, but eventually turns dark greenish to gray on the surface. The reverse is usually yellow to tan. The texture is velvety or powdery. Upon examining it microscopically, we see a single row of phialides on the upper half of the vesicle producing chains of conidia (sort of a “blowing in the wind” arrangement). The conidiophore is smooth-walled.

17. Aspergillus niger Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Aspergillus niger
Colony morphology:
Microscopic morphology:
Aspergillus niger can cause swimmer’s ear along with other Aspergillosis diseases. To identify it, the colony morphology is initially white to yellow and then turns black giving the colony a “salt and pepper” appearance. The texture is woolly. Microscopically, there is a double row of phialides covering the entire vesicle and referred to as a radiate head. The conidiophore has a smooth wall. To remember Aspergillus niger, think about Niger Bird Seed being black in color and associate it with the salt & pepper colony morphology.

18. Aspergillus flavus Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Aspergillus flavus
Colony morphology:
Microscopic morphology:
Aspergillus flavus has a yellow to green or brown colony with a downy to powdery texture. The reverse is golden to red brown. Under the microscope we see a single or double row of phialides that cover the entire vesicle radiating in all directions. The conidiophores appear roughened as the culture gets older, especially near the vesicle. My way of remembering Aspergillus flavus is that it needs a “shavus” as the rough conidiophore looks like a 5-o’clock shadow.

19. Aspergillus species Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Aspergillus species
Colony morphology:
Velvety, white, green yellow, cinnamon brown, reverse varies
Microscopic morphology:
Single or double row of phialides covering entire vesicle
Please remember that there are many other Aspergillus species. Colony morphology and microscopic morphology must be evaluated, and available resources are used to assist in their identification.

20. In Review … Aspergillus species Aspergillosis Septate / hyaline hyphae
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Septate / hyaline hyphae
In Review …
Aspergillus species
A. fumigatus
A. niger
A. flavus
Many others
Aspergillosis
The three Aspergillus species we’ve looked at are fumigatus, niger and flavus. It is important to be able to differentiate these three as they are the most common opportunistic pathogens in the Genus. They can cause Aspergillosis which is often times a pulmonary infection but can also be invasive.

21. Other Opportunistic Molds
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Septate / hyaline hyphae
Other Opportunistic Molds
Penicillium species
Paecilomyces species
Fusarium species
Sepedonium species
Other septate hyaline hyphae opportunistic molds that we will look at now include: Penicillium species, Paecilomyces species, Fusarium species, and Sepedonium species. These are all generally considered lab contaminants and rarely cause disease. A couple of these opportunistic molds are not mentioned in your objectives but I am showing them to you because they can sometimes be confused with pathogenic molds that we will discuss in another lesson.

22. Penicillium species Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Penicillium species
Colony morphology:
Microscopic morphology:
Penicillium species is a one of the most common lab contaminants that you will see. It is what grows on bread and food in your refrigerator. Its colony morphology is initially velvety and white, later becoming powdery and blue green with a white border and pale to yellowish reverse. Its microscopic exam has flask-shaped phialides that support chains of round phialoconidia giving a “brush-like” or “skeleton fingers” appearance.

23. Paecilomyces species Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Paecilomyces species
Colony morphology:
Microscopic morphology:
Paecilomyces species is not in your objectives, but is very similar in appearance to Cladosporium (a dematiaceous opportunistic mold). Its colony morphology shows a powdery, velvety, or cottony mycelium, olive green in color (or sometimes violet or brown). The microscopic exam shows a single, whorled, or penicillus-type elongated phialides (that look like “bowling pins”) bearing chains of smooth or rough, hyaline to pigmented oval conidia. The key is that there is No branching. Remember that Cladosporium had branching conidia, Paecilomyces does not.

24. Fusarium species Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Fusarium species
Colony morphology:
Microscopic morphology:
Fusarium species is an important opportunistic mold you need to be aware of. It is the most common cause of mycotic keratitis, a mold infection of the cornea. It also is a common contaminant, and has been know to hang out on your shower curtain at home. Its colony morphology is woolly or cottony, initially being white and later becomes pink or lavender (and sometimes yellow or orange), reverse is pale. Microscopically it has macrophialoconidia that are 2-5 celled, banana or cylindrical shaped, with a distinctive foot cell at the point of attachment to the phialophora. I like to think of them as little canoes.

25. Sepedonium species Colony morphology: Microscopic morphology:
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Septate / hyaline hyphae
Sepedonium species
Colony morphology:
Microscopic morphology:
The last opportunistic mold that has septate hyaline hyphae is Sepedonium species. This mold is not in your objectives, but can easily be confused with Histoplasma capsulatum. Sepedonium’s colony morphology is waxy and a white colony that rapidly becomes velvety and lemon-colored with a peripheral fringe. Its reverse is white. Microscopically, it has single or clustered, thick-walled, smooth to rough macroconidia that form at the ends of simple or branched conidiophores. This is very similar to the mold-phase of Histoplasma capsulatum, a dimorphic fungus. To differentiate the two, Histoplasma capsulatum will also have a yeast-phase that must be demonstrated.

26. In Review … Septate hyaline hyphae Opportunistic pathogens
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Septate / hyaline hyphae
In Review …
Septate hyaline hyphae
Opportunistic pathogens
Aspergillus
Fusarium
Lab contaminants
Penicillium
Paecilomyces
Sepedonium
In review, we just looked at the septate hyaline hyphae opportunistic molds. They are rapid growers and generally just lab contaminants. The two main opportunistic pathogens are Aspergillus and Fusarium. We looked at the common lab contaminants including Penicillium, Paecilomyces, and Sepedonium.

27. In Summary … Key characteristics Identification methods
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Opportunistic Molds
In Summary …
Key characteristics
Identification methods
Colony morphology
Microscopic morphology
Clinically significant opportunistic molds
Zygomycetes
Aspergillus fumigatus, A. niger, A. flavus
Fusarium species
The opportunistic molds are rapid growers and exhibit mature growth at 4-5 days. These molds are normally found in soil and their conidia are airborne. To identify the opportunistic molds, we evaluate both their colony morphology and their microscopic morphology. Clinically, they can be opportunistic pathogens but are most often contaminants. Immunocompromised patients and other predisposed situations such as diabetes mellitus are prone to infections with the opportunistic molds. The Zygomycetes, Aspergillus species and Fusarium species are the clinically significant molds in this group.

28. Aspergillus fumigatus
Who am I?
Potato Dextrose Agar
LPCB Stain of Slide Culture
Aspergillus fumigatus

29. Who am I? Rhizopus species Potato Dextrose Agar
LPCB Stain of Slide Culture
Rhizopus species

30. Who am I? Fusarium species Potato Dextrose Agar
LPCB Stain of Slide Culture
Fusarium species

31. Who am I? Penicillium species Potato Dextrose Agar
LPCB Stain of Slide Culture
Penicillium species