http://www.midwiferytoday.com/articles/garlic.asp
http://www.moondragon.org/mdbsguidelines/strepb2.html
About half way down the second link is the remedy I used- the tea tree oil and olive oil on a small tampon. I did that leading up to my GBS test, and also occassionally between the test and the birth (because testing negative does not mean you'd necessarily be negative at the time of birth, just as testing positive doesn't automatically mean you'd test positive at the time of birth, either).
The chance of transmitting GBS is only 1 in 200 if you are positive and don't receive antibiotics. If GBS is something that makes you uncomfortable enough to not want to ignore it, you could try natural remedies before the test, or natural remedies if you test positive and then retest. If you feel that the antibiotics are important for you to have, if you are birthing in a hospital you could show up in early labor for the first round of abx, leave, and then return once labor picks up for the second round. You could also have a hep lock so that you won't be tethered to an IV pole, and have it removed once the abx are complete.