An evaluation of the Bacillus content in beer

anglais. The aim of this project was to investigate how Bacillus can survive in the finished beer. This was evaluated by producing batches of beer with starter cultures that were deemed to be interesting in terms of their Bacillus content. This beer, together with beer from microbreweries and store-bought beer were plated onto Bacillus Chromoselect agar, a selective agar for Bacillus. Samples were then taken to isolate specific colonies and send them for 16S rRNA sequencing. The colony count was higher on the produced beer than in the other types. There were minor differences in CFU between the starter cultures. Since the pure cultures presented with radical differences, the similarity in finished beer would indicate that the malt contributes more to Bacillus content than the starter cultures. Bacillus cereus, or B. thuringensis, appeared to be present to a great extent in the produced beer. B. subtilis and B. smithii were dominant in the beer from microbreweries based on the 16S rRNA sequencing results. The produced beer had an average of 108.89 ±0.2 CFU/330mL, the microbreweries had an average of 104.6 ±1.23 CFU/330mL and the store-bought beer had an average of 103.8 ±0.22 CFU/330mL. Beer from larger companies was lower than those from microbreweries, this is most likely due to filtration. The amount of CFU present in these beers were close to what is used in probiotic supplements with Bacillus. Since the sequencing showed that some of the survivors were B. subtilis it is reasoned that it could have an effect on the microflora in the intestines. This is likely since B. subtilis is currently used as a probiotic supplement. There were a lot of bacteria that could not be identified below genus level. There were only two opportunistic pathogens but they were only found once.

anglais. When you take a sip of a beer from your local microbrewery you would imagine it to be safe from a hygiene point of view with no risk of getting sick from drinking the beer. In this project the main goal was to discover if a specific family of bacteria known as Bacillus can be alive in beer. Some members can cause sickness but others are used as probiotics. Which ones are alive in the beer? By checking what is growing on a specific type of nutrient solution the bacteria that are still alive in a bottle of beer are found. Judged by the way they grow and what colour they have the specific type of Bacillus can be identified but they were also sent to have their DNA analysed since this is a more specific method. Beer that have been produced in this project had a high number of living bacteria, of which some could probably be harmful. Meanwhile, beer from microbreweries and large commercial breweries had much less bacteria and they had other types which are probably not harmful. The beer from larger companies had lower amounts of Bacillus than the ones from microbreweries which could be due to that these companies do filtrations. The microbreweries do not want to do this since the yeast adds a unique flavour profile. The yeast that were used to produce beer looked different on the nutrient plates than the finished beer. The raw wort, the liquid just before adding yeast, had a lot of growing Bacillus on them. These two results together point to the raw materials having more to do with how much Bacillus is in the beer than the original idea that the starter cultures were the source of these bacteria. Since these bacteria build a hard shell around themselves when they feel threatened or starved they will survive a lot easier and could thus be present despite the boiling that is a part of the beer production. They would also be much more resistant to the low pH and the alcohol level which usually is enough to destroy microorganisms in the beer. The number of microorganisms found were close to the amount used in probiotics. Many of the identified samples were a type of Bacillus that is used as a probiotic supplement. Since the probiotic supplements have had their effects evaluated in a pill-form and not when taken as a beer it is not known how this would affect the healthy bacteria living inside of you. Judging by the probiotic ability it is not impossible that it could have an effect but there needs to be more knowledge on this subject.