Can you identify this organism?

Wow, I got lots of good feedback on the last post I did with a “name that bug” theme – so I’m going to do more! I like learning this way – especially when there’s no one around to judge you. Unknown conferences during pathology residency could be pretty brutal…but we’re all friends here – so if you don’t get the answer right, it’s not a problem – it’s just an opportunity to learn something new. How nice.

Okay. Start by taking a look at this image – maybe you’ll know right away what it is, and maybe you won’t. If you want more hints, just scroll down a little and keep reading.  The answer is at the bottom – so don’t scroll way down until you’re ready.

How do you get it?

Our mystery organism makes its home in soil. It particularly likes damp soil that’s rich with decomposing stuff (like wood and leaves). In the US, it’s seen mostly in central eastern and southeastern states (if you draw a line from the western border of Minnesota down to the eastern border of Texas, this organism doesn’t really like to live west of that line). It’s seen in Canada too.

What are the symptoms?

This organism typically just affects the lungs – but some patients do develop disseminated disease. Very rarely, the organism directly infects the skin, and just causes problems there. Most patients present with abrupt-onset productive cough, fever, chills, and chest pain. It may resolve on its own, or hang around and become chronic.

What does it look like?

The main thing you see under the microscope with this organism is suppurative (pus-filled) granulomas. Macrophages aren’t so great at killing this organism – so neutrophils come to the rescue (they’re the main cellular constituent of pus).

The organism itself is a round, with a thick (some say “double-contoured” but our photo doesn’t show that) cell wall, and – here’s the kicker – broad-based budding. In a histologic section, like this one (which is stained with PAS, by the way), you can see nice big nuclei in each round organism.

The cells in green circles are neutrophils (you can tell by their “busy” nuclei that look like Mickey Mouse ears); the yellow arrow points to the thick cell wall, the red arrows point to the nuclei, and the red oval points out the broad-based budding between two organisms.

Okay. Ready for the answer? Scroll down…



Keep going!








This organism is Blastomyces dermatitidis! Normally, I’d link the image itself – but in this case, I didn’t want you to accidentally see the answer…so here’s the link.

Here’s a recap of the main things to remember about Blastomyces and blastomycosis:

  • Lives in decomposing soil
  • Ohio and Mississippi river valleys
  • Usually just causes pneumonia, but can become disseminated
  • Rarely, localized to skin (which is probably why it got the name dermatitidis)
  • Suppurative granulomas
  • Large, round, thick-walled organisms with broad-based budding

Finally, as an aside, I remember when we were learning this in med school, we put a capital “B” by the organism, because it’s Blastomyces (obviously), and:

  • It’s pretty big
  • It shows broad-based budding
  • When it buds, it kind of looks like a capital B if you use your imagination.