Pasteurella is a common bacteria carried by many bunnies - in some bunnies it can overgrow and cause a problem called 'snuffles' or other infections. Once it has taken hold it is very difficult to cure totally although some people have a pasteurella bun who never has further episodes. One of mine is a chronic snuffler and for her it is quite bad now - but she is a netherland dwarf so she has tiny nasal passages which get bunged up quite quickly.
If you put a snuffles bun with another bun they may or may not 'catch' it - mine has lived happily with another chap for the past 2 years and he has never had any problems, it seems that most are naturally immune to it. But the problem is you can't tell which ones will and which ones wont, so generally a lot of people err on the side of caution and will only let a snuffly bun be rehomed either on their own or with another snuffly bun.
I've met Brody and she really is gorgeous