[nousermane]

It's discomforting to see "bad apple" metaphor being used to say "isolated instance with no influence to its surroundings".

That is exact opposite of how rot in literal bunch of apples behave. Spoil spreads throughout the whole lot very, very quickly.

[bobthepanda]

Also the common phrase is “a bad apple spoils the bunch.”

[btilly]

Both variations are common. "It was just a few bad apples" is the one you more often see today. But it only became common after refrigeration made it so that few people now experience what is required to successfully pack apples for the winter.