Turn-ons and turn-offs: Control of bacterial virulence gene expression

Bacteria have diverse mechanisms for establishing residence within the human host. Adhesion proteins, degradative enzymes, toxins, and other proteins ensure that the bacterial colony has food and a place to grow. The detrimental actions of these bacterial products on the human body make them virulence factors. Virulence factors are not essential to the viability of the microbe but are important for their parasitism of humans. The expression of the virulence proteins is regulated by an intricate web of turn-ons and turn-offs initiated by the signals from bacterial sensor proteins which monitor the environment of the bacteria. Osmolarity, pH, oxygen tension, and the concentrations of specific ions denote the location of the bacteria, whether inside or outside and where in the human body, and activate appropriate bacterial systems. Quorum sensors activate processes that are important for larger colonies of bacteria. The importance of these control networks for bacterial growth and disease production in the human body suggests that they may be good targets for antimicrobial drug development.