I'm no scientist, but logic states that bacteria is transmitted via oral & other contact, so whether a glass or whatever, if said object is not thoroughly cleaned afterwards then those little pesky bacterium will have a wild party!
Next person in contact with that object will surely know about it.
Disease spreads very easily, hence the use of anti-bacterial soaps in many wash-rooms, hospitals etc, all to stop bacteria being transmitted.
Hope that helps in your quest?!

Torque