Molecular and functional characterization of Enterococcus faecalis OB15: A hypoallergenic and antimicrobial starter from Tunisian Rigouta cheese

Abstract

Screening lactic acid bacteria from traditional foods is vital for identifying functional strains. Enterococcus faecalis OB15, isolated from Tunisian Rigouta cheese, was characterized for its technological, antimicrobial, and hypoallergenic properties. The strain displayed significant proteolytic activity against bovine α- and β-caseins and β-lactoglobulin, with optimal activity at pH 6.5 and 37–42 °C. Inhibitor assays indicated a metalloprotease mechanism, consistent with gelatinase (GelE) activity. In silico docking analyses confirmed that GelE targets immunodominant β-casein epitopes, generating fragments too short for antibody recognition. This structural degradation correlated with a 61% reduction in IgG immunoreactivity. Antimicrobial activity, assessed by agar diffusion assays, revealed inhibitory effects against both Gram-positive and Gram-negative foodborne pathogens, including Escherichia coli (9.5 ± 0.3 mm), Listeria innocua (8.5 ± 0.2 mm), Staphylococcus aureus (8.2 ± 0.2 mm) and Salmonella Typhimurium (8.0 ± 0.5 mm). In addition, the strain lacked vancomycin resistance (vanA/vanB) and histamine decarboxylase (hdc) genes. These findings highlight the potential of E. faecalis OB15 as a promising starter culture for the development of hypoallergenic fermented dairy products.