This study, by Sydney Finegold, M.D. and Stephen Pandol, M.D, suggests that hops have antibacterial effects on both Staphylococcus Aureus and Streptococcus Mutans. Further investigation is needed, however, there is promise in developing antimicrobial agents from hops.
See the following link:
http://gtp.autm.net/technology/view/9880