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​63. Investigating the possibility to control brewery biofilms by inhibiting quorum sensing

Erna Storgårds, VTT Technical Research Centre of Finland

 

ABSTRACT: Bacteria are no longer regarded as undifferentiated cells focused on multiplication. Cell-to-cell signaling, known as quorum sensing, is common both within and between bacterial species. Quorum sensing has also been shown to participate in biofilm formation. Because quorum sensing is not involved in bacterial growth, inhibition of signaling provides a potential means to control microbial biofilms without development of resistance. A multitude of compounds that inhibit quorum sensing signaling in bacteria have been found, many of them non-toxic secondary metabolites of fungi, plants, or algae. This study investigates the possibilities to control brewery biofilms by inhibiting quorum sensing signaling in bacteria, and it is part of a larger project aiming at reducing microbial attachment on brewery surfaces using novel methods. Several signaling molecule groups exist among bacteria. Acyl homoserine lactones (AHLs) are produced solely by Gram-negative bacteria, whereas autoinducer-2 (AI-2) molecules are produced and detected by both Gram-positive and Gram-negative bacteria. AI-2 is described as the universal signaling molecule for interspecies communication. Signaling molecules are produced and active in very low concentrations, which is why they are generally detected by bioassays. Production of AI-2 was detected from bacteria isolated from brewery filling machinery surfaces by measuring changes in the bioluminescence of Vibrio harveyi BB170, a reporter bacterium. Altogether 9 out of 20 screened strains produced AI-2. The biofilm formation ability of isolates producing AI-2, or isolates previously found to produce AHLs, was screened with a microtiter plate crystal violet assay. Fourteen strains had significant biofilm formation capability. In summary, 11 strains both produced AHL or AI-2 signaling molecules and had biofilm formation capability. Subsequently, inhibition of quorum sensing signaling with arctic berry extracts, resiniferous extracts of conifer trees, and hop extracts were studied with reporter bacteria and microtiter plate assays. Two hop extracts inhibited AI-2 mediated quorum sensing, but also the growth of the reporter bacterium at concentrations ranging from 1 to 10 mg L^–1. The principle of quorum sensing inhibitors is that they should only affect the signaling of bacteria, not their growth. Studies on the effect of berry extracts and resiniferous extracts on the detection of signaling molecules by bacteria and on their biofilm formation capability are ongoing and will be reported. This work demonstrates that AHL- and AI-2-producing bacteria are common on brewery process surfaces, and quorum sensing inhibitors could be potential means to control them. The objective is to find compounds that are suitable for incorporation into functional coating materials in brewery production plants. Incorporation of quorum sensing inhibitors into washing chemicals would be another option. Quorum sensing inhibitors have also been found to have synergistic effects with existing biocides. Eventually the breweries could employ quorum sensing inhibitors as part of novel synergistic means to control production hygiene in a sustainable and efficient way.