Quorum Sensing inhibition
Many small molecules can inhibit cGMP biosynthesis, such as the terpenoid saponin, nitric oxide generating compounds, azathioprine, or sRNAs.
Based on this, an effective strategy for eradicating food-associated bacterial biofilms is to prevent their formation by using Quorum Sensing (QS) inhibition.
Unlike bactericidal strategies, compounds targeting QS and biofilm formation cause less selection pressure and, therefore, do not develop resistance to the inhibitory compound.
Different strategies used to interfere with bacterial QS based on the inhibition of cell-to-cell communication include; competitive binding of inhibitors to the QS receptors, enzymatic degradation of QS signals, post-transcriptional control of QS genes via sRNAs and inhibition of QS signals biosynthesis.
Another strategy involves the use of paraoxonases. Paraoxonases are a type of QQ enzymes found in root-associated fungi and various plants. Plant compounds with QSI activities include the red alga Delisea pulchra and disulphide compounds from garlic and rosmarinic which prevent biofilm formation in P. aeruginosa.
Organic acids are another type of QQ in the food industry. For example, 2% of lactic acid produced a 1 log reduction in E.coli and Salmonella spp. numbers. Citric acid and acetic acid have also QS potential but to a lesser extent than lactic acid.
Examples from other natural sources include:
- Extracts from grapefruit and grapefruit juice which showed QS inhibition in Vibrio harveyias well as in coliO157:H7, S. enterica and P. aeruginosa.
- Extracts from different North American plant species (Bucidabuceras, Callistemon viminalis, and Conocarpus erectus) were effective against aeruginosabiofilm formation.
- Green tea polyphenols diminished protease activity and trimethylamine production in Shewanella baltica, inhibiting its biofilm formation.
- Nigella sativa seed extract binding to zinc NPs interfered with motility and matrix production during the initial attachment and also during the biofilm maturation by coli, L. monocytogenes, and P. aeruginosa.
Further reading about quorum sensing and biofilms
Li, Y. H., & Tian, X. Quorum sensing and bacterial social interactions in biofilms. Sensors (Basel, Switzerland), 12(3), 2519–2538, 2012. https://doi.org/10.3390/s120302519.
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