Competition Studies Confirm Two Major Barriers That Can Preclude the Spread of Resistance to Quorum-Sensing Inhibitors in Bacteria

Abstract

The growing threat of antibiotic resistance necessitates the development of novel antimicrobial therapies. Antivirulence agents that target group-beneficial traits in microorganisms (i.e., phenotypes that help the cells surrounding the producer cell instead of selfishly benefiting only the producer cell) represent a new antimicrobial approach that may be robust against the spread of resistant mutants. One prominent group-beneficial antivirulence target in bacteria is quorum sensing (QS). While scientists are producing new QS inhibitors (QSIs) at an increasing pace for use as research tools and potential therapeutic leads, substantial work remains in empirically demonstrating a robustness against resistance. Herein we report the results of in vitro competition studies in Pseudomonas aeruginosa that explicitly confirm that two separate barriers can impede the spread of resistance to QSIs: (1) insufficient native QS signal levels prevent rare QSI-resistant bacteria from expressing their QS regulon, and (2) group-beneficial QS-regulated phenotypes produced by resistant bacteria are susceptible to cheating by QSI-sensitive neighbors, even when grown on a solid substrate with limited mixing to mimic infected tissue. These results underscore the promise of QSIs and other antivirulence molecules that target group beneficial traits as resistance-robust antimicrobial treatments and provide support for their further development.

Control of Biofilm Formation: Antibiotics and Beyond

“…of biofilm-viable cells (70) Quorum-sensing inhibitors Inhibition of cell-to-cell or cell-to-surface attachment QSIs possess high species specificity and effectively act against certain pathogens (138) Reported toxicity of and resistance to QSI (136) Essential oils Attack cellular ATP and ATPase, acting on cytoplasmic enzyme and membrane proteins/fatty acids leading to the leakage of metabolites and ions (94) Have a broad-spectrum activity against a wide range of pathogenic microbes (93) Some EOs produce oxidative stress and possess toxic properties, inducing killing activity against eukaryotes (141) Anti-quorum-sensing activity by downregulation of QS genes leading to reduced virulence factor production and biofilm formation (94) Have been used as ethnomedicine against bacterial infection and cancer for a long time (95,96) Increased albumin level and skin irritation (see review by Patel et al [141])…”

Can resistance against quorum-sensing interference be selected?

“…In these studies, the QS-deficient mutants mimic those cells sensitive to the quencher (sensitive or S cells) because these cells have QS turned off, whereas the wild-type strain mimics those resistant individuals (resistant or R cells) able to produce QS signals and public goods in the presence of the quencher. (Gerdt and Blackwell, 2014) The method of using mimics originated with Mellbye and Schuster (2011). Like in precedent studies, adenosine-dependent growth of P. aeruginosa was studied, (Gerdt and Blackwell, 2014) and competition experiments in mixtures of QQ-sensitive (S) and QQ-resistant (R) variants were performed using different R/S ratios.…”

A surprising range of modified-methionyl S-adenosylmethionine analogues support bacterial growth

“…Our original interest in the range of AdoMet derivatives that can support growth derived from the fact that AdoMet is also required for production of bacterial quorum signalling molecules, such as acylhomoserine lactones (Churchill & Chen, 2011) and furanosyl borate diesters (Galloway et al, 2011), that control virulence in many Gram-negative pathogens. There is particular interest in identifying agents that would reduce bacterial pathogenicity [possibly without strong selection for resistance (Gerdt & Blackwell, 2014)] by interfering with quorum sensing but not with growth or viability (Defoirdt et al, 2010;Hodgkinson et al, 2012;Kalia, 2013;Rutherford & Bassler, 2012). Our approach has been to identify methionine analogues that are substrates for the bacterial MAT orthologues (called MetK in many bacteria), and that yield AdoMet analogues which are selectively non-functional in acylhomoserine lactone (AHL) biosynthesis.…”