Every office has that colleague who leaves their food in the fridge, or cup on their desk, a little too long and things start to get a little funky! In the histology lab that person may come in handy, if you’re looking for controls for your fungus stains like GMS. An easy way to get control tissue for fungus is just to grow your own. It is a fun and gross science experiment, which is right up the histotech’s alley, and it works pretty well!
Basically, you just need to let something get moldy! We’ve seen people use bread, a mold blob from a sweet tea left out, cheese. Orange peels are very commonly used. Moisten the orange peel and leave it out for a week to mold. Cut it into pieces, then fix, process and embed. If you are finding that the counterstain is washing out add a piece of some other tissue like skin to catch the natural carbs and counterstain.
If you find the orange peel doesn’t work, try something like blue cheese that is already fungus. Take the blue parts, wrap it in tissue paper and run it through your processor as usual.
The important thing to consider though before attempting these methods, is whether or not your pathologist and/or your organization’s policies allow non-human tissue to be used as a control. Many want to be able to compare the control tissue with the specimens your lab processes, apples to apples comparison (no orange peel puns intended). Make sure that whatever you end up using is validated and appropriate for your lab’s requirements.
If you can’t use food, another viable option if you are in an organization with a microbiology department is to have them grow some control for you. When you receive fresh lung tissue, after it has been grossed put a few pieces in a petri dish and take it to microbiology. Have them add some fungal material and put it in the incubator to grow for a few weeks. Once you get it back from them, it can get the same fixation time and processing as the patient tissue.
Another option is just to use past positive patient tissue containing fungus, though that is much less of a fun science experiment!