SELECTION AND CHARACTERIZATION OF NATIVE Enterococcus STRAINS WITH ANTIMICROBIAL POTENTIAL ISOLATED FROM ARTISANAL MANUFACTURED CHEESES

Enterococcus are part of indigenous microbiota of artisanal cheeses and contribute to the development of the aroma and ripeness of cheeses. Some strains synthesize antimicrobial peptides called enterocins that can suppress the growth of foodborne pathogenic microorganisms. The aim of this research was to select and characterize native strains of Enterococcus with antimicrobial activity isolated from artisanal cheeses. For their isolation, the samples were seeded in bile esculin agar and MRS agar. Phenotypic characterization as well as the detection of antimicrobial substances were carried out by biochemical, bilayer and diffusion on agar methods, respectively. Of 68 strains isolated, Enterococcus faecium was the predominant species, followed by Enterococcus durans and Enterococcus faecalis. Nine strains also showed antimicrobial activity against taxonomically related bacteria and food-borne pathogens. Enterococcus faecium Qpa.1 and Qpa.2 strains exerted a very effective antagonistic effect against Listeria monocytogenes. The antimicrobial substance produced by E. faecium QPa.1 was inactivated by trypsin and a-chymotrypsin, but not by catalase. In addition, this activity was stable at pH 3 and 9, at 100 degrees C for 20 min and at 4 and -20 degrees C for 180 days. In conclusion, Enterococcus faecium QPa.1 produced an active and specific bacteriocin against Listeria monocytogenes, which could be used as a bioprotective culture for the preservation of cheeses.