Selection of potential probiotic Enterococcus faecium isolated from Portuguese fermented food

Abstract

Four Enterococcus faecium strains isolated from fermented products were evaluated for potential use as probiotic strains. In addition to efaAfm gene, commonly found in E. faecium food isolates, none of the isolates possessed virulence genes and none had positive reactions for the production of tyramine, histamine, putrescine and cadaverine in the screening medium used. All of these four isolates proved to be resistant to 65°C. E. faecium 119 did not show antimicrobial activity against any of the target bacteria investigated. E. faecium 85 and 101 inhibited Listeria innocua and E. faecium DSMZ 13590. The strain E. faecium 120 inhibited seven target bacteria (Listeria monocytogenes 7946, L. monocytogenes 7947, L. innocua 2030c, L. innocua NCTC 11286, E. faecium DSMZ 13590, Enterococcus faecalis ATCC 29212 and Staphylococcus aureus ATCC 29213) and was chosen as the representative to assess the ability to survive gastrointestinal tract passage simulation, as well as the protective role of two food matrices (skim milk and Alheira) during its passage. For both matrices used, no significant differences (p<0.05) were obtained between the types of digestion — quick and slow passage simulation. In the skim milk matrix the isolate was reduced to values below the detection limit of the enumeration technique by the end of the two digestions, in contrast to the Alheira matrix, for which isolate 120 showed a reduction of only ca. 1logCFU/ml. The E. faecium strain 120 was shown to be a potential candidate for further investigations as a potential probiotic culture.