Well, I don't think padding would breed bacteria any more than any other material. Of course, I don't think about stuff like that, for anything, really. All my sports bras get washed in hot water and hung up to dry...
You may think it is silly, but it's not to me. If something makes me feel better about the way I look, than I am going to do it. There's always a lot of discussion about finding larger sized bras and the problems inherent with having large breasts. Frankly, it's almost impossible to even find bras in an A cup size, especially sports bras. Thankfully, I live near a real lingerie shop where I buy my regular bras, after years and years of wearing ill fitting ones.
Off topic, but...
It's the same with petite sized clothes. I am short, always have been. I like stylish clothes. I cannot just walk into a store and buy a t shirt. Even stores that have petite sized pants or skirts rarely have petite sized t shirts/tops. There are 2 places that I can buy things at. On the other hand, there's plenty of larger sizes. Stores increase their plus size departments and get rid of the petites. I know as a society we are getting taller and heavier, but please, there are plenty of flat chested women under five foot four who would appreciate some choices.