Cytotoxicity of Bacteriocins Produced by Four Enterococcus faecium Strains Isolated from Cheese

Introduction: Bacteriocins are compounds produced by several bacterial strains in order to compete with other microorganisms contained in the same micro-habitats. In recent years, these compounds have been proposed for use as biological preservatives for certain food products. Bacteriocin-producing bacteria are relatively common but often these substances may have in addition of bactericide effect, a profile of toxicity to humans and animals that impedes the use of these substances.

Purpose: Therefore, the aim of this study was to analyze the cytotoxicity of partially purified bacteriocins isolated from four different bacterial strains.

Methods: Bacteriocins produced by Enterococcus faecium ST209GB, ST278GB, ST315GB and ST711GB were partially purified from 24-hour cultures grown in MRS broth by precipitation with ammonium persulfate and hydrophobic chromatography separation column SepPakC18. Huh7.5 cells derived from human hepatocarcinoma were seeded in 96-well plate and subsequently treated with increasing concentrations of bacteriocins. Two days after initial treatment, MTT was added to cells and colorimetric intensity was obtained at wavelength of 562 nm. The values obtained were transformed into percentage of viability compared to negative control (untreated).

Results: The tested bacteriocin concentrations ranged from 10 µg/ml to 160 µg/ml. In two strains (ST315GB and ST711GB) of four tested bacteriocin the CC₅₀ value was close to 80 µg/ml. Moreover, for the substance produced by the strain ST209GB CC₅₀ was approximately of 160 µg/ml. Finally, the viability of the bacteriocin produced by the strain ST278GB, at the highest tested concentration was 85%, and therefore it was not possible to estimate the value of CC₅₀. All strains showed cell viability above 90% when tested at a concentration of 10 µg/ml.

Significance: In several studies attention has focused on the antimicrobial properties of bacteriocins, however, as evidenced in this work, often these compounds have a cytotoxicity profile that would impede the use of these substances as biopreservatives.