Tolerance of brewing microorganisms to silver nanosurfaces

Beer is a poor and rather hostile environment for most microorganisms comprising poor nutritional availability, ethanol concentration ranging from 4-5%, pH's ranging from pH 3.8 to 4.7, high carbon dioxide concentration (approximately 0.5% w/w) and extremely low oxygen content (<0.1 ppm). These conditions are ideal for strict anaerobes such as Pectinatus spp. And Megasphaera spp. Pectinatus spp play a major role in 20/30% of bacterial incidents, mainly in nonpasteurized beer rather than in pasteurized beer. The most characteristic feature of spoilage caused by Pectinatus spp. is extensive turbidity and an offensive 'rotten egg' smell brought by the combination of various fatty acids, hydrogen sulphide and methyl mercaptan. This spoilage activity can cause serious damages for breweries. Megasphaera has emerged in breweries along with Pectinatus and is responsible for 3-7% of bacterial beer incidents. Beer spoilage caused by this organism results in a similar extreme turbidity as Pectinatus and the production of considerable quantities of butyric acid together with smaller amounts of acetic, isovaleric, valeric and caproic acids as well as acetoin. Like Pectinatus, the production of hydrogen sulphide causes a fecal odor in beer. Titanium dioxide (TiO2) is receiving considerable research interest as a photocatalyst and consequently an antimicrobial coating. Titanium dioxide thin films have been formed on glass, steel and other surfaces by a wide range of techniques, especially by sol/gel and chemical vapour deposition. Commercial products making use of TiO2 photocatalyst include self cleaning glasses such as Pilkington Activ and Saint Gobain Bioclean, self cleaning tiles (TOTO Inc.) and in air purifiers. The ability of silver/titania thin films to act as antimicrobial coatings has received scant attention, although one report on preliminary antimicrobial tests showed that the coating halts E. coli colony formation. The use of silver as a microbicide is well known and a host of commercial products exist for use in wound dressings, ear-pieces, face masks, catheters, plasters and even for deodorisation of socks. A number of commercial antimicrobial surface treatments also exist which rely on the microbicidal activity of the Ag+ ion/these include AgION (AgION Technologies Inc.) and SilvaGard (AcryMed Inc.). In all of these instances the silver is impregnated in the products in its nanoparticulate form or as a silver salt such as silver nitrate. Recent presentations (European Brewing Convention, 2007 and American Society of Brewing Chemists, 2007, unpublished data) from Erna Storngaards (VTT, Finland) suggest that Silver may represent an effective antimicrobial agent against key brewery spoilage bacteria. It is suggested that silver and silver/TiO2 composite coatings may (1) prevent biofilm formation in brewery vessels and pipes, (2) limit microbial loading during final pack filling and (3) increase microbial stability in final pack. Specific Objectives of the Proposed Study 1) Materials scientists will develop nanoparticles or thin surface technologies to produce surfaces for assessment of antimicrobial activity (Prof Steve Howdle). 2) The surfaces will be assessed for durability, tolerance to brewery based cleaning agents and surface coverage using nanotechnology approaches (Prof Clive Roberts). 3) The susceptibility of production and wild yeast, lactic acid bacteria and anaerobic final pack spoilage microorganisms to the surfaces will be assessed (Prof Katherine Smart). 4) Action of the active surface components on cellular function on Pectinatus and Megasphaera spp will be established to identify mode of kill and potential for resistance acquisition to be established (Prof Katherine Smart).