Mauro Libi Crestani: Does one bad apple really spoil the whole bunch?

The answer is a big YES. The riper a piece of fruit is, the more ethylene it produces. This leads to a concentration of the gas that’s enough to over ripen all the fruit. Given the right conditions and enough time, one apple can push all the fruit around it to ripen—and eventually rot.
Additionally, an apple that is infested with mold will contaminate other fruit it's stored with as the mold seeks additional food sources and spreads. In both cases, it actually does take just one single apple to start a domino chain that ruins the rest of the bunch.
This example has been used so many times as an analogy for an employee with a bad attitude.  If a company has an employee who doesn't care about the company it its customers, comes in late every day, doesn't carry her weight of the work load, that will affect the attitude of the other employees. Why should I do all the work when she gets the same salary and does nothing. That attitude will spread among the employees. Soon you will have many more employees that have bad attitude and it will continue to spread. 
When creating an office team of positive motivated employees , it is important to keep them motivated. Reward good behavior to show the team that good attitude and hard work is rewarded. It is equally important to get rid of the employees with bad negative attitude as they are truly are bad apples and if allowed to stay on the team they will spoil the whole bunch.