The isolated L. monocytogenes strain demonstrated hemolytic activity. Lopez et al. (2006) suggested that between 8 and 21% of the food and environmental isolates of L. monocytogenes have attenuated virulence or are completely avirulent. In vitro assays that detect phenotypic markers, such as hemolytic activity, provide information
about virulence. The hemolytic activity found in the isolated strain evidenced an active virulence. Thus, it represents a risk for pigs consuming these feeds. The antimicrobial activity between LAB remains a significant criteria for the selection of the most promising strains to be employed in later studies with other microorganisms. Our results
are in agreement with a previous study presented by Oliveira et al. (2008b). However, different results to those found in this study were presented by Saidi et al. (2011), who tested homologous antimicrobial activity between LAB and observed that only 22.93%
of them had an inhibitory effect on the growth of other lactic bacteria. This percentage is much lower than that observed in this study with LAB isolated from brewer's grains (59%). Listeriosis in animals is mainly related to the consumption of feeds contaminated with L. monocytogenes. Preservation methods such as drying or using chemical preservatives can prevent microbial growth. Nevertheless, these types of solutions have many drawbacks such as the alteration of the organoleptic and nutritional properties of foods, among other. Currently, alternative methods are being developed. LAB have been recognized as beneficial microorganisms and it is well known that produce many antimicrobial metabolites such as organic acids, bacteriocins, hydrogen peroxide,
among others. The present study shows that LAB isolated from brewer's grains produce antilisterial compounds which inhibit L. monocytogenes growth. As in this study, Teixeira de Carvalho et al. (2006) and Kivanc et al. (2011) found that all tested lactic bacteria inhibited a strain of L. monocytogenes. However, the number of indicator strains was higher in our work. On the other hand, Albano et al. (2007) and Singh and Prakash (2009) obtained results that do not coincide with those reported in this study. They found that certain strains of LAB did not inhibit the growth of L. monocytogenes.