Lactobacillus plantarumisolated from kefir protects vero cells from cytotoxicity by type-II shiga toxin fromEscherichia coliO157:H7

Abstract

Kefir is a fermented-milk beverage originating and widely consumed in the Caucasus as well as in Eastern Europe and is a source of bacteria with potential probiotic properties. EnterohaemorrhagicEscherichia coliproducing Shiga toxin is commonly associated with food-transmitted diseases; the most prevalent serotype causing epidemics isEsch. coliO157:H7. The aim of this study was to evaluate the antagonism ofLactobacillus plantarumisolated from kefir against the action on Vero cells of supernatants of theEsch. coliO157:H7 strain 69160 expressing the type-II Shiga toxin (Stx2) and to study the role of theLactobacilluscell wall in that inhibition. Spent culture supernatants ofEsch. coliO157:H7 strain 69160 led to cytotoxic effects on cultured eukaryotic cells as evidenced by the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide–cleavage assay or by lactate-dehyrogenase release.Lb. plantarumCIDCA 83114 reduced the cytotoxic activity of Stx present in strain-69160 supernatants, and this protection was markedly higher than those ofLactobacillus kefirCIDCA 83113 and 8348 andLb. delbrueckiisubsp.bulgaricusCIDCA 333. This antagonism of cytotoxicity was mimicked byLb. plantarumcell walls but was reduced after heating or protease treatments, thus indicating a protein or peptide as being involved in the protection mechanism. The cell surface of the lactobacilli bound the subunit B of Stx thereby decreasing the cytotoxicity. These interactions could constitute the first step in preventing the damage induced byEsch. coliO157:H7 supernatants, thus representing a valuable means of potentially mitigating the noxious effects of this food pathogen.