Here we are on Part 4 of the Aspergillus series!! If this is your first visit, please be sure to check out the previous posts covering: Aspergillus fumigatus, Aspergillus niger, and Aspergillus flavus. I was just talking to my ‘mycology mentor’ the other day about this series, and he asked me if I’d ever heard of where the term “Aspergillus” came from? I said, “No.” He made me go look it up 😀 ! So, Aspergillus got it’s name from a device used by priests to douse people with holy water. This device was called an Aspergillum (or less frequently, aspergilium or aspergil). There’s this whole story from Leviticus in the Bible about 2 birds, and one gets dipped in blood, and then the blood gets sprinkled on somebody and they get purified. So many words. You can read all about it on Wikipedia here if you haven’t already. The shape of this device is the same shape as a conidial head of Aspergillus! The device has a handle (like a conidiophore) and at the end is a large bulb (like a swollen vesicle). The bulb has lots of little holes in the top and holds water in the bottom portion. The device is shaken to release water and the water droplets look like chains of conidia floating away!
This week, we’re talking about Aspergillus versicolor! I’ve just kind of been going along in the order of frequency in which I see these guys in our lab. I realized while I was working on this that so far it happens to be the same order in which they’re discussed in my fungus Bible. You guys, if you are looking for pretty much the ONLY medical mycology text that you need: Davise Larone’s Medically Important Fungi. It’s like the Cliffs Notes for medical mycology, and condenses information from ALL THE MYCOLOGY BOOKS for you. And Dr. Larone herself hand drew those illustrations. *sigh* I love her.
As with most Aspergillus, this organism is widespread in the environment. It can sometimes be considered a contaminant, but it is known to occasionally cause infection in various sites on the body. It most commonly infects the lung, but is also known to cause onychomycosis (nail infection).
The macroscopic colony morphology of Aspergillus versicolor growth on agar is often described as “suedelike” in texture. It tends to have numerous radial grooves or folds in the growth, and the color varies. It can be shades of green, tan, yellow, orange, or pink. The reverse can be white, yellow, orange, red…geeze…hence “versicolor.” The colony I took these pictures from was mostly orange, with a white periphery, with patches of dark green in the center. The reverse was a deeply pigmented brick color. Sometimes they’re ready for their micro show at 3 days, but I feel these tend to mature a little bit slow…more like 5 days.
The microscopic morphology of Aspergillus versicolor is very interesting. The first time I saw this species, I thought I was looking at a mixed slide. This species forms the typical swollen Aspergillus heads that we’re used to seeing, but also forms smaller conidial heads that resemble penicilli. I was so perplexed because my growth on the agar plate appeared pure. After some investigating, I discovered what I was looking at…versicolor! Now if we’re looking at the typical conidial head, biseriate phialiades loosely cover half to all of the swollen vesicle. Smaller conidial heads have a vesicle that is so small that you can hardly see it! And the phialides are arranged in a way that looks brushlike, similar to penicillium! Hülle cells (a sterile cell produced by cleistothecia during the sexual state) are occasionally present. In the photos above, you can actually see hülle cells! I’m so excited because when I took those photos, it was the first time in my life I’d ever seen hülle cells. And I just took those photos yesterday. I’m not kidding. I’ve been around fungus 9 years, and this was the first time I’d ever seen hülle cells. Yay!