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.
The CFS of all of the LAB strains assayed showed antilisteria
activity on LM1. By comparison, some strains showed a lower
antagonistic effect while others showed none when LAB supernatants
were neutralized. These results agree with those recently
reported by Aguilar and Klotz (2010). They reported antimicrobial
activity of CFS from Lactobacillus species and found a higher
inhibitory effect with untreated supernatants, as compared to