Methods for selectively manipulating a growth rate of a selected bacterium comprising the step of contacting the selected bacterium with a predetermined amount of a quorum sensing molecule to affect a change in the growth rate of the selected bacterium, wherein the quorum sensing molecule is species specific, and the change in the growth rate is dependent on the amount of quorum sensing molecule in a dose-dependent fashion. Also provided are methods for treating or protecting against bacterial infections by utilizing the dose-dependent response of bacterial quorum sensing systems. The methods can be applied to a wide range of bacteria species including Streptococci, Staphylococci, and Bacilli. Compositions, medicaments and oral formulations for use with the methods are also disclosed.