Characterization of enterococci isolated from homemade Bulgarian cheeses and katuk

A collection of 107 lactic acid bacteria (LAB) isolates was obtained from traditional Bulgarian dairy products—homemade cheeses and katuk samples, produced from heat-treated cow, goat, ewe and buffalo milk without the addition of any bacterial starter culture. The samples were collected from mountain region of Rhodope (south part of Bulgaria), Tracian valley and mountain region of Stara Planina (west part of Bulgaria). These LAB produced bacteriocin-like inhibitory substances (BLIS) and proteinases. Preliminary strain determination was performed according to their fermentation ability using API 50CHL and API 20 Strep. Most of the characterized strains (58) belong to genus Enterococcus; 21, 20 and 11 strains were identified as Lactobacillus sp., Streptococcus sp. and Lactococcus sp., respectively. Isolated enterococcal strains were characterized using phenotypic features as well as by DNA typing. The strains were identified as Enterococcus faecium (34), Enterococcus durans (22) and Enterococcus faecalis (2). The proteolytic activity varied from 0.094 to 0.455 mM/L Gly into the group of E. faecium and from 0.109 to 0.487 mM/L Gly into the group of E. durans strains, while both E. faecalis strains showed relatively high proteolytic activity. The samples obtained after 3 h of hydrolysis of β-casein by E. faecalis B1 strain were further used for mass spectrometry analysis, and 31 peptides were identified.