Since the 1960s, group B streptococci (GBS) have lost genetic diversity, yet they cause more virulent neonatal infections and show high rates of tetracycline resistance. The puzzle is that tetracycline is not used to treat GBS. Nevertheless, since the 1950s, most GBS clones were wiped out by the collateral effects of the widespread use of tetracycline and other antibiotics, even though they were not the treatment target. Da Cunha et al. show that a few GBS clones survived by virtue of their persistence or virulence, and these clones also acquired mobile genetic elements carrying a mixture of antibiotic resistance genes, including those for tetracycline resistance….