However, the relationship is not always a happy one. Sometimes "bad" bacteria get inside people - and cause them to commit anti-social acts - such as leaving a trail of liquid feces behind them whereever they go. This is good for the bacteria, but not so good for the humans. We say that such people have diarhoea.
Memes are not always good for their host humans either. One of the manifestations of some types of bad memes is verbal diarhoea. You've probably encountered the type: pyramid marketing enthusiasts, conspriacy theorists, apocalyptic missionaries, people trying to recruit you for their preferred cause or religion. Of course a certain amount of talking can be good for you - but too much talking is probably good for the associated memes, but not so good for their hosts. Those with verbal diarhoea are taking their talking too far.
The expression verbal diarhoea is an interesting case of folk cultural epidemiology.