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Quorum sensing (QS) refers to the ability of bacterial pathogens such as Pseudomonas aeruginosa to regulate their gene expression based on cellular density. One such cell–cell signaling system — the Pseudomonas quinolone signal (PQS) system — responds directly to quinolone selection pressure.
Xia et al. used QS receptor gene knockout bacteria to show that the PQS system is a key component in the development of quinolone resistance under sublethal ciprofloxacin selection pressure. Phenazine biosynthesis was upregulated with the emergence of quinolone resistance (including pyocyanin, a phenazine pigment virulence factor produced by P. aeruginosa). A pyocyanin-deficient strain exhibited attenuated quinolone resistance under selection pressure t…