The opportunistic bacterial pathogen Pseudomonas aeruginosa causes chronic lung infections in cystic fibrosis (CF) patients. Importantly, virulence factor expression and biofilm formation in P. aeruginosa is coordinated by quorum sensing (QS) and one of the key QS signaling molecules is 3-oxo-C12-HSL. Remarkably, a tetramic acid, (C12-TA), with antibacterial properties is formed spontaneously from 3-oxo-C12-HSL under physiological conditions. Seeking to better understand this relationship, we sought to investigate whether 3-oxo-C12-HSL and C12-TA may be contributing factors to the overall pathogenicity of P. aeruginosa in CF individuals and if their detection and quantitation in sputum samples might be used as an indicator to assess disease states and monitor therapy success in CF patients. To this end, 3-oxo-C12-HSL and C12-TA concentrations were initially analyzed in P. aeruginosa flow cell biofilms using liquid chromatography coupled with mass spectrometry (LC–MS). A liquid chromatography tandem mass spectrometry (LC–MS/MS)-based method was then developed and validated for their detection and quantification in the sputa of CF patients. To the best of our knowledge, this is the first report to show the presence of both the quorum sensing molecule (3-oxo-C12-HSL) and its rearranged product (C12-TA) in human clinical samples such as sputum. A total of 47 sputum samples from 20 CF and 2 non-CF individuals were analyzed. 3-Oxo-C12-HSL was detected and quantified in 45 samples with concentrations ranging from 20 to >1000 nM; C12-TA was found in 14 samples (13–900 nM). On the basis of our findings, quorum sensing autoinducers merit further investigation as biomarkers for infectious disease states.

Simultaneous activation of signaling pathways requires dynamic assembly of higher-order protein complexes at the cytoplasmic domains of membrane-associated receptors in a stimulus-specific manner. Here, using the paradigm of cellular activation through cytokine and innate immune receptors, we demonstrate the proof-of-principle application of small molecule probes for the dissection of receptor-proximal signaling processes, such as activation of the transcription factor NF-κB and the protein kinase p38.

•Quorum quenching could be an alternative to or act synergistically with antibiotics.•Prophylactic quorum quenching approaches have demonstrated efficacy in vivo.•Quorum sensing antigens might warrant inclusion in microbial vaccination strategies.•Neutralization of quorum sensing molecules may restore proper host immune function.•Development of drug-resistance against quorum quenching strategies remains unclear.With the emergence of microbial pathogens increasingly resistant against commonly used antibiotics, new treatment strategies are desperately needed. Bacterial quorum sensing has attracted a lot of attention over the last decade as a potential new target for antimicrobial therapy. Interference with quorum sensing signaling, or quorum quenching, might offer new avenues to prevent and/or treat bacterial infections via inhibition of virulence factor expression and biofilm formation. While many inhibitors of quorum sensing signaling have been described, only few have been evaluated in vivo and none has been clinically developed. This review will highlight recent findings and discuss interesting future areas where quorum quenching might be a promising strategy.