cycloheximide

Cycloheximide is an antibiotic. It interferes with protein synthesis by inhibiting the peptidyl transferase activity of the 60S ribosomal subunit in eucaryotes. Thus, this includes inhibition of growth of fungi, yeasts and protozoa (and other eukaryotes).
Researchers use this stuff for "counter selection": when you want just a certain type of organisms one way is to give them their favourable food, another way is to kill off their competitors.

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