Switches, cross-talk and memory in Escherichia coli adherence.

Escherichia coli is a successful commensal and pathogen. Its pathogenic diversity stems from the acquisition and expression of multiple virulence-associated loci. Many of the key virulence factors are surface structures involved in adherence and motility. These are important antigens and their expression is limited by phase-variable genetic switches that are considered to act randomly. This review considers the possibility that such stochastic expression within a bacterial population belies sequential or co-ordinate control at the level of the individual bacterium. Co-ordinated expression or cross-talk between virulence loci can lead to a programmed set of events within a bacterium analogous to a simple form of electronic memory that is of benefit during infection.