neutralized supernatants. Similar findings were obtained by Sica
et al. (2010), who stated that all CFS from LAB showed antimicrobial
activity on L. monocytogenes, and only some supernatants
maintained their inhibitory activity after being neutralized with 5 N
sodium hydroxide. The authors explained that the loss of antimicrobial
activity after neutralizing the supernatant was due to the
fact that the strainswere only capable of producing organic acids. In
contrast, Botina et al. (2008) found that the supernatants of 11 LAB
did not show antimicrobial activity on L. monocytogenes when
tested by the well diffusion method. Also, Mezaini et al. (2009)
demonstrated that only 2 LAB supernatants inhibited the growth
of the pathogen. In a recent study with lactic bacteria from fish,
Marguet et al. (2011) showed that 7 of 74 CFS (9.45%) presented
antilisterial activity. While the percentage found by these authors is
very low, our results are in agreement because CFS of some strains
maintained their activity on Listeria spp. after being neutralized.
In conclusion, the isolation of lactic acid bacteria with antilisterial
activity from brewer's grains is promising based on their
capacity to produce antimicrobial compounds and not only organic
acids. The production of antimicrobial metabolites by LAB in the
substrate would generate an unfavorable environment for the
growth of the pathogenic bacterium under study. Further studies
are needed in order to determine the potential efficacy of these
bacteria as antilisterial agents.