Chemical Communication-Do We Have a Quorum?

There are two types of bacterial communication systems, those in which the signal produced by bacteria isdirected only at other organisms, and those where the signal is detected by others and self. The latter is involved inadaptation to the environment. The adaptation signals are autoinducers, the response is population density-dependent andhas been termed "quorum sensing". Our current knowledge of bacterial signaling systems indicates that Gram positivebacteria use small peptides for both types of signaling, whereas Gram negative organisms use homoserine lactones asautoinducers. Gram- negative bacteria internalize the signals which act upon an intracellular receptor. Gram-positivebacteria use the signals as ligands for an extracellular receptor of a two-component signaling system. Inhibitors of quorumsensing compounds for both Gram positive and Gram negative bacteria are being explored. Signal inhibitors could bepotentially effective in impeding biofilm formation, which might prolong the utility of the currently available antibioticsin this era of antibiotic resistance. In this review, we will explore both bacteria-host and bacteria-bacteria communicationsystems, with an emphasis on inhibitors of these systems both natural and synthetic.