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Although unicellular, bacteria are highly interactive and employ a range of cell-to-cell communication or ‘quorum sensing (QS)’ systems for promoting collective behaviour within a population. QS is generally considered to facilitate gene expression only when the population has reached a sufficient cell density and depends on the synthesis of small molecules that diffuse in and out of bacterial cells. As the bacterial population density increases, so does the synthesis of QS signal molecules and consequently, their concentration in the external environment increases. Once a critical threshold concentration is reached, a target sensor kinase or response regulator is activated, so facilitating the expression of QS-dependent target genes. Several chemically distinct families of QS signal molecules have been described, of which the N-acylhomoserine lactone (AHL) family in Gram-negative bacteria have been the most …