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Abstract
The present study focused on probiotic characterization and safety evaluation of Enterococcus isolates from different artisanal dairy products. All the isolates exhibited inhibitory activity against several food spoilage bacteria and food-borne pathogens, including Shigella flexneri, Staphylococcus aureus, Listeria monocytogenes, Yersinia enterocolitica, Klebsiella pneumoniae, Escherichia coli, and Bacillus subtilis. The PCR results indicated the presence of at least one enterocin structural gene in all the tested strains. The Enterococcus isolates were further evaluated regarding their safety properties and functional features. The isolates were susceptible to vancomycin, gentamycin, and chloramphenicol. The results of PCR amplification revealed that all the tested isolates harbored none of the tested virulence genes except E. faecalis (ES9), which showed the presence of esp gene. The Enterococcus isolates showed cholesterol lowering properties. The selected isolates showed a high tolerance to low pH, and toward bile salts. They also demonstrated hydrophobicity activity, auto-aggregation, and adhesion ability to the human intestinal Caco-2 cell line. These properties may contribute the bacteria colonizing the gut. This study revealed that the Enterococcus isolates, especially E. durans ES11, ES20 and ES32, might be excellent candidates for production of functional foods to promote health benefits.
Highlights
Enterococci are belonging to genera of lactic acid bacteria (LAB)
The highest survival rate was observed for isolate ES20 (81.6 ± 0.3%), followed by isolates ES32 (77.4 ± 0.3%) and ES11 (76.3 ± 0.2%), while the lowest survival rate was observed for isolate ES16 with 10.3 ± 0.1% survival rate
After treating with protease enzymes, the clear zones around the halos were disappeared. It could be because of proteinaceous nature of secreted metabolites by isolates. It has been shown by some studies (Balla et al, 2000; Cintas et al, 2000) that bacteriocins secreted by Enterococcus isolates are strong inhibitors of food-borne pathogens such as S. aureus, L. monocytogenes and Clostridium tyrobutyricum
Summary
Enterococci are belonging to genera of lactic acid bacteria (LAB). They are Gram-positive, catalase negative, cocci-shaped, facultative anaerobe, and non-spore forming bacteria (Haghshenas et al, 2016). Based on phylogenetic evidence and molecular studies (16S-rDNA sequencing or DNA– DNA hybridization), more than 26 species were classified in this genus. These microorganisms are ubiquitous bacteria which present as common microbiota in the intestine of humans, mammals, and other animals gastrointestinal tracts, but they are exist in soil, water, vegetable products, meats, fermented and cooked meat and dairy products (Li et al, 2018; Zommiti et al, 2018). Significant role of E. faecium, E. faecalis, and E. durans in the ripening of traditional cheeses have
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