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Location in the brewery: biofilms and microbial communities

Anaerobic GNB most likely have long been brewery inhabitants and emerged as beer spoilers when the conditions in beer permitted anaerobic growth, rather than these bacteria coming into breweries coincidentally with the implementation of improved beer packaging which produced greatly reduced oxygen content. This hypothesis is indirectly supported by the same temporal emergence of spoilage by Pectinatus and Megasphaera in well-separated countries on different continents. Pectinatus spp. are widely distributed, perhaps due to their slightly higher oxygen tolerance than Meg- asphaera spp. Pectinatus spp. have been isolated in breweries in at least a dozen countries, including the USA; Japan; Finland, Norway, and Sweden; Belgium, France, Germany, Spain, the Netherlands, and the United Kingdom; and most recently, the Czech Republic (Lee et al., 1978; Matoulkova et al., 2012b; Paradh et al., 2011; Suikho and Haikara, 2001). In contrast, Megasphaera isolates have been reported in fewer, but still widely separated countries, including in Australia, Finland, Germany, Sweden, and the United Kingdom; and most recently, Canada (Bergsveinson et al., 2017; Paradh et al., 2011; Suikho and Haikara, 2001).

Additional evidence for Megasphaera and Pecti- natus having a long-term association with breweries is based on the relative ease and frequency with which these bacteria are found. The recent papers by Paradh et al. (2011) and Matoulkova et al. (2012b) document this, as isolation of Megasphaera and Pectinatus (particularly P frisingensis) was readily achieved directly from beer, and even fermenting wort and yeast slurries, and from various sampling points within the brewery packaging environment. Both research groups emphasized that Megasphaera and Pectinatus are likely maintained within biofilms in the brewery and if stringent cleaning and hygiene are not maintained, such biofilms persist, continually acting as a potential source from which the bacteria can spread and contaminate yeast suspensions, fermenting wort, and most importantly, packaged beer. That at least Pectinatus isolates appear to be able to spread via aerosols within the brewery emphasizes the need for continued vigilance for the presence of biofilms and anaerobic GNB in all areas of a brewery, not just in the filling area (Back, 1994).

It has been suggested that brewery biofilms containing anaerobic GNB also include aerobic bacteria and yeast (to consume the oxygen in the immediate locale), as well as lactic acid bacteria (LAB; to provide lactate used as a carbon source for the anaerobic GNB growth) (Back, 1994). The frequent finding of both LAB and anaerobic GNB within a given brewery setting fits with this scenario (Back, 1994; Paradh et al., 2011). In contrast, research specifically focused on microbes composing biofilms has not been as supportive, in that anaerobic GNB were found in only 3 of 78 samples taken from the bottling areas of two breweries in one study (Timke et al., 2005a) and in none of the samples similarly collected from a single brewery in a second study (Timke et al., 2005b). In contrast, a more recent analysis of 58 isolates obtained from sampling biofilms in a single brewery filling hall were analysed by MALDI-TOF MS, and P frisingensis and S. lacticifex were identified 3 and 19 times, respectively (Vavrova et al., 2014). This variability in frequency of anaerobic GNB isolation and identification is probably primarily due to differences in hygiene operating procedures in the different breweries sampled in the respective studies. Of secondary importance are the sampling and bacterial identification methods used. The limited and variable information available strongly suggest the need for more research on the role of biofilms in maintaining anaerobic GNB in the brewery setting.

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