1. Grp B strep is a common bacterium often carried in the lower genital tract, and is almost always harmless.
2. Yes, it can be transmitted this way, but because it can be contracted other ways and is typically harmless it is not considered an STI.
3. It can move back and forth between partners, but you both likely have antibodies against it by now, so there is little risk of it causing serious illness. For women, it is usually only an issue during pregnancy.
1. Makes sense to take an antibiotic if you are having symptoms that might be related. You could clear the infection...at least temporarily.
2. The immune system can usually clear it on its own, or keep it in check so that it does not spread.
3. She could get tested and treated if her doctor agrees, but it should not stop you from having sex, as it is not harmful.
4. That's a tough one. :-) The prostate can harbor bacteria, some good, some not so good. Antibiotics can upset the balance, but can also prevent more serious infections. I would seek your urologist's advice on this. He most likely will not change his approach based on the strep B as it is considered not pathogenic in otherwise healthy individuals.