A total of 13,802 samples over seven years were investigated using real‐time PCR for the presence of beer spoilage bacteria, providing a rare large‐scale overview of the incidence of individual species. At the same time, the isolation site (early stages of the brewing process = type I and late stages = type II) and the type of contaminated beer and intermediate products (bottom‐fermented or top‐fermented) were evaluated using chi‐squared analysis. The most frequently occurring species were Lactobacillus brevis (7 year average 41.9%), Lactobacillus (para‐)casei (10.4%) and Lactobacillus backii (9.5%). L. (para‐)casei was found at significantly higher rates in the early stages of the brewing process, whereas Lactobacillus lindneri, the Lactobacillus [L. (para‐)plantarum and L. coryniformis] and the Pectinatus (P. cerevisiiphilus, P. frisingensis and P. haikarae) groups and Megasphaera cerevisiae predominated in the later stages and in package (significance level 95%). On a significance level of 95%, Pediococcus damnosus, M. cerevisiae and L. lindneri together with the Pectinatus and Lactobacillus groups grew predominantly in bottom fermented samples. L. brevis, in contrast, was found most frequently in top fermented beers. Copyright © 2018 The Institute of Brewing & Distilling
Aims: Over the past few years, the lactic acid bacteria (LAB) species Lactobacillus rossiae has appeared on occasion as a beer spoiler, in addition to its role as an inhabitant of sourdough and other foods. Many authors have described the L. rossiae sourdough isolates as phenotypically and genotypically extremely versatile. This characterization was confirmed in a comprehensive genotypic and phenotypic study based on 11 beer-related L. rossiae isolates. Materials and methods: The beer-related isolates and the L. rossiae type strain were classified in a polyphasic approach applying 16S rRNA, rpoA and pheS housekeeping gene sequence comparisons, DNA-DNA hybridization and rep-PCR technique. Additionally, carbohydrate fermentation and amino-acid metabolism were examined. In terms of the beer-spoilage ability, the growth in two different beer types was examined and the presence of three prominent hop resistance genes (horA, horC and hitA) and of one gene presumably responsible for the production of exopolysaccharides (gtf) was checked. Conclusion: The carbohydrate fermentation pattern (GTG) 5 rep-PCR and the pheS gene sequence comparison showed deviations between sourdough and beer-related isolates. DNA-DNA hybridization values and the pheS gene sequence comparison between beer-related isolates point towards the need for expansion of the limits for species description. Significance and Impact of the Study: Lactobacillus rossiae shows great phenotypic and genotypic variability stretching the limits of species description. The correlation between pheS gene sequence and the presence of the horC gene is important for brewing microbiologists and the search for beer-spoilage prediction methods.
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