Modulating Gram-positive bacteria quorum sensing systems

Developing methods to manipulate bacterial quorum sensing systems have attracted significant interest as a potential strategy for attenuating infection. In contrast to antibiotics or antimicrobial agent, which aim at killing bacteria or inhibiting their growth, blocking cell-to-cell signalling mechanism, could attenuate bacterial pathogenicity without imposing the level of selective pressure on a bacterial population to develop resistance. We explore the quenching of the PlcR – PapR quorum-sensing system in Bacillus cereus group as a model bacterium for Gram-positive human pathogens. A set of synthetic 7‑mer PapR-derived peptides (PapR₇; ADLPFEF) have been shown to inhibit efficiently the PlcR regulon activity and the production of virulence factors, reflected by a loss in hemolytic activity without affecting bacterial growth. Interestingly, these inhibitors involved D-amino acids or alanine replacements of either proline (P) glutamic acid (E) or phenylalanine (F) of the heptapeptide PapR. Using amino acids substitution strategy, we designed and characterized the second PapR₇-derived combinations, alternate double and triple alanine and D-amino acids replacement at these key positions. We found the role of proline and glutamic acid on PlcR regulon activation and demonstrated that the D-Glutamic acid substitution is crucial for the design of better PlcR antagonists. Our findings demonstrate the potential of two PapR₇-derived peptide generations to serve as quorum-quenching agents of B. cereus QS. We propose our approach to explore other QS system in human Gram-positive pathogens.