Detection of spoilage bacteria in beer by polymerase chain reaction

Cultivation methods for the detection of bacteria in beer, although simple and sensitive, are time-consuming and lack specificity. In this study, the sensitivity of a polymerase chain reaction (PCR) assay consisting of an easy sample treatment and specific primers for Lactobacillus lindneri, L. brevis, Megasphaera cerevisiae, and Pectinatus spp. was improved by pre-enrichment. A pre-enrichment broth supporting the growth of lactobacilli and anaerobic beer spoilers better than currently used media was formulated. For determination of the pre-enrichment times needed for PCR detection of these contaminants, artificially contaminated beer samples were mixed with the pre-enrichment broth and incubated anaerobically at 30°C. Low levels of lactobacilli (≤10 CFU/100 ml) were detected after 1–3 days, Pectinatus spp. after 2–4 days, and M. cerevisiae after 2–3 days of pre-enrichment, depending on the strain and the alcohol content of the beer. After the pre-enrichment, the PCR analysis took <8 hr. The time saving compared to corresponding conventional methods requiring up to several weeks is marked, especially for L. lindneri, M. cerevisiae, and Pectinatus spp. Moreover, the assay described allows species- or genus-level detection of the most harmful beer spoilage bacteria in finished beer and is sensitive and simple enough for routine work.