Cysts of Pneumocystis jiroveci (formerly carinii) in bronchoalveolar lavage, Grocott’s methenamine silver stain.

In this induced argentaffin reaction, chromic acid oxidation forms aldehydes from fungal cell wall polysaccharide components. The reaction is similar to the Periodic acid Schiff reaction, but since the chromic acid is a much stronger oxidizer, background staining by collagen and basement membrane is suppressed (they are oxidized past the aldehyde stage).  The aldehyde groups then react with the silver nitrate, reducing it to a metallic silver, thus blackening the site.

It can be a bit tricky to time since different organisms take up stain at different rates. Pneumocystis can be missed if you understain, but other organisms will come out a black blob (thus making it impossible to see the internal structure) if you overstain.

False color SEM of Aspergillus sp conidiophore. I lost the source on this so if someone has it, please send it my way!

Apologies for the slow goings lately; I’ve had a mess of things on my plate (pun intended). Hopefully things will pick up soon.

Chlamydospores in Candida albicans, wet mount.

The Dalmau test was used to help ID C. albicans once upon a time but phased out before I got into the labs. It was essentially growing a yeast in unfavourable environments to see if they formed chlamydospores in response to the stress. Cornmeal agar (minimal nutrient qualities) was used and the inoculum would be covered with a coverslip to decrease the amount of oxygen available to the growing yeast.

Epidermophyton floccosum, wet prep.

The person who was teaching me mycology had an incredible accent and for the longest time I thought she was telling me to look for “puddle shaped macroconidia”. I couldn’t figure out for the life of me why anyone would describe anything as puddle shaped. It wasn’t until the end that I realized she was saying paddle shaped. Oops. They remain “puddles” in my mind though.

Epidermophyton floccosum is one of the dermatophytes, fungi that cause superficial infections of hair, skin, and nails. They generally aren’t a big deal, but there’s a lot of money in antifungals because man, do people hate dandruff and athlete’s foot.