NOTE: The original question asked for a
"Soft version or alternative for 'A rotten potato spoils the whole bag.'"
After I posted an idiomatic English alternative, a moderator edited the question and left a comment saying,
"I don't understand how changing potatoes to apples makes this politer."
Obviously, it does not. This was my answer to the original question with a new EDIT at the end to better address the update made to the question by gtiwari333:
The common English idiom is
"a rotten apple spoils the barrel."
Proverb. Example: "A bad person influences everyone he or she comes into contact with, making them bad too. Helen is the rotten apple that spoils the barrel in our office. Everyone sees her come in late to work and take long coffee breaks, and they think, "'Why can't I do the same?'"
"One rotten (or bad) apple spoils the barrel."
"A single bad influence can ruin what would otherwise remain good."
"Or take the one about 'a few bad apples,' the reflexive defense whenever misconduct surfaces in the midst of some organization, from Enron to Abu Ghraib to Haditha to the mortgage meltdown. It's an ancient bit of counsel, whether it's said of bad apples or rotten ones, or of bushels, barrels, baskets or bins. Benjamin Franklin had it as 'the rotten apple spoils his companion,' which goes back to Shakespeare's time."
Historically, this blog claims
The saying hails from John Northebrooke in his book entitled, “A Treatise Wherein Dicing, Dauncing (etc.) Are Reproved” published in 1577. The exact passage was:
A penny naughtily gotten, sayth Chysostoms, is like a rotten apple laid among sounde apples, which will rot all the rest.
Long before John Northebrooke, however, there was Geoffrey Chaucer (1343 – 25 October 1400). In his “Canterbury Tales” readers come across the following passage in unfinished “The Cook’s Tale.”
Uppon a proverbe that seith this same worde:
“Better ys rotten appulle out of an hurde
Than for to let hem rote alle the remenaunte.”
And ryght so it fareth by a ryotes servaunte.
This passage loosely translates as this:
About an old proverb, the words that say:
“A rotten apple‘s better thrown away
Before it spoils the barrel.” That is true
When dealing with a bad apprentice too.
EDIT: In response to your update, perhaps you could gather your team together and talk about how the attitudes and actions of each team member affect everyone else on the team, pointing out that when one team member has a negative attitude or bad work habits, others tend to become discouraged and the whole team suffers.
You might point out that none of us wants to be the proverbial bad apple or rotten potato that spoils the whole bag, so each of us needs to make a concerted effort to be more positive, more collegial, and more productive.
If this doesn't work, you may need to speak with the difficult person privately. Listen compassionately and offer kind suggestions for how to improve their interactions and performance in the workplace. Perhaps the person is dealing with problems outside of work, with family or with health issues. Together, you can write down the areas in which improvement is needed. Then both of you can sign, date and keep a copy of the list so that you have documentation of the discussion and can review it together again on a specific date, perhaps the following month. Participating in the review and knowing when the list will be re-visited are important motivators for improvement.