I'd go with the plague, that one is cool and I think there is a fear that it will be used as a bioweapon. Many of the stuffed microbes are pathogens but not used (that I know of) as bioweapons. Oh wait I think there was a case of salmonella being used by some religious cult on the west coast. Then you could always see if one is the same shape as a bioweapon and use it instead.
~~Nonpathogenic microbes are our friends~~