Food-Grade Bacteria Combat Pathogens by Blocking AHL-Mediated Quorum Sensing and Biofilm Formation

Abstract

Disrupting bacterial quorum sensing (QS) signaling is a promising strategy to combat pathogenic biofilms without the development of antibiotic resistance. Here, we report that food-associated bacteria can interfere with the biofilm formation of a Gram-negative pathogenic bacterium by targeting its AHL (acyl-homoserine lactone) QS system. This was demonstrated by screening metabolic end-products of different lactobacilli and propionibacteria using Gram-negative and biofilm-forming Chromobacterium violaceum as the QS reporter and our anti-QS microscale screening platform with necessary modifications. The method was optimized in terms of the inoculation technique and the concentrations of D-glucose and L-tryptophan, two key factors controlling the synthesis of violacein, a purple pigment indicating the activation of the QS system in C. violaceum. These improvements resulted in ca. 16-times higher violacein yields and enabled revealing anti-QS effects of Lactobacillus acidophilus, Lentilactobacillus kefiri, Lacticaseibacillus rhamnosus and Propionibacterium freudenreichii, including new cheese-associated strains. Our findings also suggest that acetate and propionate excreted by these species are the main factors that interrupt the QS-mediated signaling and subsequent biofilm growth without affecting the cell viability of the C. violaceum reporter. Thus, the present study reports a revised anti-QS screening method to accurately define new bacteria with an ability to combat pathogens in a safe and sustainable way.

Quorum Sensing in Biofilm

“…When tested extensively against AHL QS in P. aeruginosa, the novel phenolic derivative GM-50 reduces biofilm-related virulence, thereby enhancing antibiotic efficacy [111]. In addition, food-associated bacteria such as lactobacilli can exploit antibiofilm activity by interfering with AHL QS [112]. The efficacy of probiotics against QS has been indicated in previous studies.…”

Synthesis and Biological Evaluation of New Quinoline and Anthranilic Acid Derivatives as Potential Quorum Sensing Inhibitors

“…The developed compounds were first pre-screened for their anti-QS and bactericidal activities using the C. violaceum ATCC 31532 strain as the reporter and the previously established optimized conditions for 96-well format [39]. In this reporter strain, the activation of QS induces the expression of genes contributing to biofilm formation and the simultaneous synthesis of a deep-purple violacein [35] that can be quantitatively monitored [37,38].…”

“…Also, the concept of hybridization has been previously employed by various research groups within the subject area [32][33][34]. In this study, the generated hybrid compounds were first pre-screened for their anti-QS/biofilm and bactericidal activities using a Gram-negative Chromobacterium violaceum-based microscale screening platform, which allows compounds with genuine anti-QS activity to be distinguished from those with bactericidal activity in one single experiment [24,[35][36][37][38][39]. C. violaceum is also an opportunistic pathogen capable of causing severe and potentially fatal manifestations in both immunocompromised and non-compromised hosts [40], and, therefore, serves as a suitable reporter for screening therapeutic agents.…”

Quorum sensing-related activities of beneficial and pathogenic bacteria have important implications for plant and human health

“…QS-signalling can organize competing strategies to neighbouring microbes. For example Gram-positive Propionibacteria, like Propionibacterium freudenreichii , have promising probiotic properties (Rabah et al 2017 , Savijoki et al 2023 ). Progress in defining such metabolic interactions by in situ screening test was made possible by using biofilm-forming C. violaceum as a QS-reporter and a microscale screening platform.…”

“…Progress in defining such metabolic interactions by in situ screening test was made possible by using biofilm-forming C. violaceum as a QS-reporter and a microscale screening platform. In this way, anti-QS effects of Lactobacillus acidophilus, Lacticaseinbacíllus rhamnosus, P. freudenreichii , and other cheese-associated strains could be identified as potent competitors for virulent pathogens (Savijoki et al 2023 ).…”