Is there an indirect or polite way to say "A rotten potato spoils the whole bag" ?

I looked up online but didn't found a good one.

UPDATE

I want to use it in a situation as below:

Suppose you notice someone in your team acting as a "rotten potato". As a leader you gathered the team to behave nicely and be aware of such potato but in a indirect way so that everyone including the "rotten potato" will be aware of and do not take it badly.