I know that you've put the implications of over use of antibiotics, but what about the implications of have GBS (correct name is actually Streptococcus agalactiae) untreated? It can cause a urinary tract infection (which is of increased risk with pregnancy), premature labour, and PROM (premature rupture of the membranes) in the mother. As well as sepsis, meningitis, fever and respiratory distress in newborns, it can also cause a post partum infection for the mother - such as endometritis, with can lead to a pelvic abscess and septic shock.

Not only can having a LVS/HVS (low vaginal swab/high vaginal swab) taken and screened for GBS, it can also be used to screen for other organisms (such as for colonisation of Escherichia coli). Also, when I was working in a microbiology laboratory attached to a maternity ward, we *occasionally* found colonisation of Listeria monocytogenes in vaginal swabs.

Information taken from Bailey & Scott's et al Diagnostic Microbiology