Negativity

I have come to realize that some people are not happy unless they are complaining.  I find myself working with staff members who always have an issue with something.  I can not remember anytime they were positive about anything.  The days become stressful and they start complaining about any and everything.  How do you change this person, can you change a persons personality?  If not, how do you work with people who are the counter opposite of you?