Contamination under the microscope: telling bacteria, mould and debris from spores
Not everything on a spore slide is a spore. Learning to recognise bacteria, mould and debris is part of microscopy, and it is also how you judge whether a syringe was made properly. Here is what each looks like and what it means.
01What a clean slide looks like
A drop from a well-prepared syringe shows spores, water, and very little else: perhaps a few fragments of gill tissue from the print and the odd air bubble. Spores are large, regular, thick-walled objects at 400x. Everything that is not one of those is worth a second look.
02Bacteria
Bacteria are tiny next to a mushroom spore: rods and dots a fraction of a micrometre across, often in motion, sometimes in chains or clumps. At 400x they show as a fine shimmering grain in the background; at 1000x individual cells resolve. A syringe with a bacterial load looks milky rather than hazy to the naked eye and may smell on opening. Bacteria in a syringe mean it was filled without a hood or the water was not sterile. It is the most common contaminant, and the one sterile preparation exists to prevent.
Not everything on a spore slide is a spore.
03Mould spores and hyphae
Mould spores are much smaller than cubensis spores, usually round or short-ellipsoid, often green, grey or colourless, and frequently in chains or clusters. Hyphae are the threads: long, branching, sometimes with cross-walls. A syringe with mould shows visible strands or a fuzzy clump inside the barrel. Mould in a syringe usually means the print was contaminated before it was suspended.
04Yeast and debris
Yeast cells are round to oval, smaller than mushroom spores, thin-walled and often budding. Debris (dust, fibres, gill fragments) is irregular and inconsistent in size. Neither is a spore, and neither is a disaster in small amounts; both in quantity mean a sloppy preparation.
05Judging a syringe
- Fine, even haze, clean spores on the slide: good.
- A few fragments of tissue: normal.
- Milky water, shimmering background, smell: bacterial; discard.
- Strands, clumps, fuzz: mould; discard.
- Mostly empty spore walls and debris: old or heat-damaged.
MycoWorld fills every syringe in a flow hood from a logged print into sterile water, which is why a clean slide is the normal result. Any specimen that arrives otherwise is replaced on a photo and a LOT number.
06Contamination as a subject
For a microscopist, contaminants are not only a problem to avoid. A deliberately aged drop on a slide, sealed and left a few days, is a lesson in bacterial growth and in what a spore looks like among things that are not spores. Just keep it well away from your clean specimens.
Specimens for this story: DreadMaw (Gamma Decay iso), MRRL (Melmak Revert), Project Bluebook (CG isolation) and Bluey Vuitton, all prepared under sterile protocol and LOT-logged in the UK.
Questions people ask
Why is my spore syringe cloudy?
A fine, even haze is spores and is normal. A milky cloud, strands or clumps mean bacteria or mould, and the syringe should be discarded and replaced.
How do I tell mould spores from mushroom spores?
Size and regularity. Mushroom spores are large, uniform and thick-walled; mould spores are far smaller, often in chains, and usually with hyphal threads nearby.
Does MycoWorld replace contaminated syringes?
Yes. Email a photo and the LOT number.