4. Discussion
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.