Sporeforming bacteria in beer: Occurrence, diversity, presence of hop resistance genes and fate in alcohol-free and lager beers

Abstract

The aim of this study was to assess the occurrence of sporeforming bacteria in different types of beers (n = 163) and to assess the presence of hor genes in the isolates. Additionally, the study aimed to evaluate the fate of five representative sporeforming bacteria harboring horA and horC genes in alcohol-free and lager beers. Two hundred and sixty (n = 260) sporeforming bacteria belonging to eight different genera were isolated from beers, i.e., Bacillus (n = 118), Paenibacillus (n = 89) and Brevibacillus (n = 41), Lysinbacillus (n = 6), Cohnella (n = 3), Rummeliibacillus (n = 1), Alicyclobacillus (n = 1), and Anoxybacillus (n = 1), respectively. A predominance of members within the Bacillus cereus sensu lato (n = 72; 27.1%), followed by B. megaterium (n = 18; 7%), P. validus (n = 16; 6.1%), P. humicus (n = 13; 5%), P. alginolyticus (n = 13; 5%) and Br. brevis (n = 13; 5%) was observed in beer samples analyzed. Only 5% (n = 14) out of 260 sporeforming bacterial isolates recovered from beers harbored one or both horA and horC genes. Only one (0.3%) isolate, i.e., Bacillus cereus sensu lato (identified as B. thuringiensis LMQA 206) presented both horA and horC genes. None of the five bacterial sporeforming strains harboring horA or horC genes inoculated was able to grow in the beers throughout the storage period studied, and no spoilage was detected. The results of this study indicated a widespread occurrence of sporeforming bacteria in several types of beers from different brands, highlighting that measures should be taken to reduce the occurrence of sporeforming bacteria considering stability and safety concerns.