Technical Session 18: Microbiology II Session
Erna Storgårds, VTT Technical Research Centre of Finland
Co-author(s): Outi Priha and Riikka Juvonen, VTT Technical Research
Centre of Finland, Finland; Kaisa Tapani, Sinebrychoff, 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.
Erna
Storgårds holds a Ph.D. degree in microbiology from Helsinki
University. She joined the VTT Technical Research Centre of Finland in
1988. From 1988 to 2007 she worked with brewery microbiology and process
hygiene, first as a research scientist or senior scientist, later as
group manager and team leader. In 2008 she took over responsibility for
the VTT Culture Collection; in addition to that, she also takes part in
projects in her field of expertise. She has been a member of the EBC
Microbiology Group, later the EBC Brewing Science Group, since 1992 and
its chair (2004–2008); chair of the EBC Microbial Contaminants Subgroup
(1993–2004); and a member of the Microbiology Subcommittee of the EBC
Analysis Committee (1998–2008). She has been a member of ASBC since
2004.
