Judith,
You are right on point! Ignoring issues can create negative energy. Managers sometimes struggle with redirecting people with negative energy or addressing negative people, which have strong opinions. One on one coaching works well, as opposed to confronting them in front of the group. It is also important to be specific. Telling an employee to, "stop being negative" is not that helpful. Rather, focus on the specifics of the behavior and how it is impacting the team. For example, "rolling your eyes when other employees make suggestions is making people uncomfortable" or "I have noticed that you are not prepared for the meetings and your read your emails during the meeting. These behaviors convey that you are not interested in our projects."
The direct approach can work wonders for turning around or minimizing negative activities.
Good luck!
Dr. Jamie Morley