Microbiology of brewing production - bacteria of the order Enterobacterales and culture methods for their detection

Petra Kubizniaková,Kateřina Štulíková,Dagmar Matoulková,Eva Vontrobová,Katarína Hanzalíková,Martina Brožová

doi:10.18832/kp2019.66.345

Petra Kubizniaková, Kateřina Štulíková + Show 4 more

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https://doi.org/10.18832/kp2019.66.345

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Abstract

The growth of 7 strains belonging to the order of Enterobacterales, represented by the species of Citrobacter Freundii, Enterobacter cloacae, Escherichia coli, Klebsiella oxytoca, Obesumbacterium proteus, Rahnella aquatilis, Raoultella terrigena, Serratia marcescens and Shimwellia pseudoproteus, was monitored on selected cultivation media. Three types of agars - Endo, MacConkey and Chromocult Coliform agar together with two incubation temperatures of 28 and 37 °C were tested under aerobic conditions. The aim of the study was to detect such essential enterobacteria harmful to beer that cannot be proven at 37 °C, which is the temperature usually used in operational laboratories in breweries. Our results showed that most of the tested strains of enterobacteria were able to grow at 28 °C on all selected types of agar. The exception was just the representatives detection of which is problematic at 37 °C. Nevertheless, a little or no growth was always observed on just one of the tested media.

Highlights

This article follows a review paper entitled Microbiology of brewery production – bacteria of the order of Enterobacterales (Matoulková et al, 2018)
Members of Shimwellia, Obesumbacterium, Rahnella, Citrobacter, Klebsiella, Raoultella, Serratia and Enterobacter genera were found in breweries
Due to the sensitivity of enterobacteria to ethanol and acidic pH, their growth and ability to multiply in the finished beer is minimal and they occur mainly as a contamination of production yeast

Summary

Introduction

This article follows a review paper entitled Microbiology of brewery production – bacteria of the order of Enterobacterales (Matoulková et al, 2018). The Enterobacterales order contains 7 families with more than 40 bacterial genera that are isolated from diverse types of environments. Pathogenic species, including Escherichia coli, have not been detected in breweries (Van Vuuren and Priest, 2003). Contaminated water or unsatisfactory hygienic condition of surfaces and equipment (e.g. leakage of pipe connection) represent other usual sources of enterobacteria (Vaughan et al, 2005). These bacteria are harmful since they produce undesirable sensory substances (e.g. diacetyl and dimethyl sulphide) at the beginning of the main fermentation. Some species are involved in the formation of carcinogenic N-nitrosamines (Boulton and Quain, 2001)

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