You are frequently in a situation where samples or cultures must be ‘clean’ or ‘sterile’ or monoxenic’. Assess what the needs are. Making axenic cultures is time-consuming. If you can get away with one eukaryotic species among many prokaryotes, then go for that.

Many protozoa eat other protists and probably cannot be grown clean.

Standard bacteriological practices apply.

Use autoclaved (120°C heat = about 15 psi pressure for 20 minutes) media and equipment that is sterile. Remember not to autoclave plastic containers.

If you need to control contamination, an open flame over a 70% alcohol-swabbed bench is often sufficient; but remember that the air contains protozoan and fungal spores. Sterilize your hands and arms with alcohol (don’t make the mistake of doing this just before reaching over the flame). Open culture vessels and other containers only near the flame, and flame the openings before and after transfers.

You can also use sterile fume hoods.

The simplest procedure for making sterile media is to pass source water through a 0.2 µm filter, although this is not absolutely guaranteed to create a fully sterile medium.

Simple media

For protozoa

0.2 µm filtered source water

'Eau de Volvic' or other low mineral content spring water if freshwater

Heat sterilized rice or barley grains can be added to finance the bacterial growth that many protozoa depend on

For algae

F2 or G medium

Soil water biphasic medium

Agar plates

2% agar in filtered source medium