This is the first report on the isolation of L. monocytogenes from brewer's grains used for swine feed. This finding is important because we were able to isolate this microorganism despite the acidic conditions of the fermented substrate. Adaptation of
L. monocytogenes to acidic environments involves mechanisms that maintain intracellular pH homeostasis by directing Hþ ions out of the cell and by consumption of internal Hþ through decarboxylation reactions, generation of ammonium ions, and macromolecule repair by heat shock proteins (Ivy et al., 2012). Currently, there is no available information on the isolation of L. monocytogenes from brewer's grains. L. monocytogenes is pathogenic to animals and humans and often contaminates food and feed, leading to losses in pig production. L. monocytogenes also represents an indirect risk to healthy people that consume contaminated pork meat. In a related study, Belceil et al. (2003) isolated L. monocytogenes in 6 (14%) samples of wet feedstuff for swine production. This result differs from that found in the present work. In addition, Oliveira et al. (2008a) found a higher incidence of L. monocytogenes (15%) in silage samples from the north of Portugal using microbiological methods. This substrate shares some similarities with brewer's grains as both suffer fermentation processes and are used for animal nutrition. However, the incidence of L. monocytogenes found in this study is coincident with that presented by Konosonoka et al. (2012), who obtained a percentage of 4.7 from silage samples destined for feeding pigs.