PROBIOTIC PROPERTIES OF ENTEROCOCCUS STRAINS ISOLATED FROM THE SILAGE

This study aimed to identify and evaluate the probiotic properties of five Enterococcus strains isolated from the silage using in vitro screening assays. Their metabolites, antibiotic susceptibility, antimicrobial activity, as well as their survival in the gastrointestinal tract (GIT) and adhesive ability to human intestinal cells were investigated. Among eight selected antibiotics, all the isolates showed sensitive traits to six particular antibiotics including tetracycline and vancomycin. L2-L5 showed inhibition zones against Escherichia coli and Salmonella except that L6 only inhibited the growth of E.coli. The GIT proved that all the strains were able to survive in low pH and bile salt conditions and they all can adhere to LS-174T intestinal cells. L2 and L5 were then chosen to examine their competition activity toward E.coli and inflammatory response. The results showed that both strains exhibited strong competition activities toward E.coli. The displacement ratios were 98.4 and 97.7%, respectively. Compared with E.coli, L2 showed lower stimulation of interleukin (IL)-8 and IL-1, while L5 induced higher levels of cytokines to provoke an inflammatory response. Finally, the in vivo effect of L2 was investigated. The data showed that L2 was harmless. The results obtained suggest that L2 is potentially probiotic. Practical ApplicationEnterococci are lactic acid bacteria that occur frequently in large numbers in various foods including vegetable, meat and dairy products. However, some of these bacteria are also recognized as nosocomial pathogens. Several properties may be evaluated to prove the potential of the bacteria before using them as probiotics. Results of this study indicated that five Enterococcus strains isolated from the mixed grass and corn stalk silage exhibited different capacties of antibiotic susceptibility, antimicrobial activity, tolerance to gastrointestinal conditions, adhesion to intestinal cells, and competitive exclusion of E.coli adhesion to epithelial cells and stimulation of immunity. Among these strains, L2 shows above-average results in all probiotic criteria observed in vitro. Additionally, L2 was evaluated to be safe in mice feeding. The findings of our study suggest that L2 isolated from the silage may be potentially used as probiotic in humans.