Beer enemy number one: genetic diversity,physiology and biofilm formation of Lactobacillus brevis

Lactobacillus brevis is the most significant beer spoilage bacteria worldwide. It is found as a contaminant at all stages of brewing, including during primary and secondary fermentation, storage, filtration and the packaging process. In production with flash pasteurisation and subsequent hygienic filling, avoiding and tracing secondary contaminations is the key to a microbiologically stable product. However, L. brevis strains vary in their spoilage potential and can grow in many different beer types. This study presents a physiological test scheme for growth potential and biofilm formation in various media. It was determined that a large number of L. brevis strains can form biofilms as a first coloniser. The identification of the species alone is therefore not enough to be sure of the spoilage risk, which shows the need for a more in depth differentiation. DNA fingerprint techniques are crucial to differentiate isolates of this species at strain level. The rep‐PCR fingerprint system (GTG)₅ was used to differentiate a selected collection of 20 isolates, which were characterised in growth and biofilm formation in various media. The data showed a high variation within the selected isolates. As second step, generated fingerprint clusters of L. brevis were traced back to contamination sources in a German brewery, revealing a high number of isolates with potentially varying growth, spoilage and biofilm potential. L. brevis being the demonstrator species, the PCR system used is a powerful and compatible tracing and troubleshooting tool for all kinds of spoilage bacteria in the brewing industry. © 2019 The Institute of Brewing & Distilling