Population-level virulence factors amongst pathogenic bacteria: relation to infection outcome.

The study of population-level virulence traits among communal bacteria represents an emerging discipline in the field of bacterial pathogenesis. It has become clear over the past decade-and-a-half that bacteria exhibit many of the hallmarks of multicellular organisms when they are growing as biofilms and communicating among each other using quorum- sensing systems. Each of these population-level behaviors provides for multiple expressions of virulence that individual free-swimming bacteria do not possess. Population-level virulence traits are largely associated with chronic or persistent infections, whereas individual bacterial virulence traits are associated with acute infections. Thus, there is a natural dichotomy between acute and chronic infectious processes, which helps to explain the medical community's success in combating the former, but its utter failure in dealing with the latter. The recent recognition of multicellularity among chronic bacterial pathogens will lead the way towards new multimodality therapies.