Figure 1.

QS mechanism in gram-categorized species. The canonical QS signaling and the Agr system are the most typical processes involved in the biofilm formation in gram+ bacteria S. aureus. This system includes four genes (AgrA-D) under the control of one operon. The products of this operon include virulence factors such as toxins and proteases. AgrD is converted to autoinducer peptides (AIPs) during secretion through AgrB to out of the cell where it activates the transmembrane AgrC by phosphorylation. The activated AgrC further activates AgrA that promotes the expression of targeted genes by influencing two promoters (P2 and P3). P2 regulates the Agr operon system, and P3 activates the expression of RNAIII which is the key regulator of different factors relating QS and biofilm formation. RNAIII upregulates virulence factors and inhibits factors contributing to bacterial dispersal. The balancing function Agr proteins on bacterial swarming and infection makes them promising targets for developing therapeutic antibiofilm agents [69].