Lactobacillus plantarum LB95 impairs the virulence potential of Gram-positive and Gram-negative food-borne pathogens in HT-29 and Vero cell cultures

Listeria monocytogenes, Salmonella enterica and verocytotoxigenic Escherichia coli (VTEC) are amongst the most important agents responsible for food outbreaks occurring worldwide. In this work, two Lactobacillus spp. strains (LABs), Lactobacillus plantarum (LB95) and Lactobacillus paraplantarum (LB13), previously isolated from spontaneously fermenting olive brines, and two reference probiotic strains, Lactobacillus casei Shirota and Lactobacillus rhamnosus GG, were investigated for their ability to attenuate the virulence of the aforementioned pathogens using animal cell culture assays. In competitive exclusion assays, the relative percentages of adhesion and invasion of S. enterica subsp. enterica serovar Enteritidis were significantly reduced when the human HT-29 cell line was previously exposed to LB95. The relative percentage of invasion by Listeria monocytogenes was significantly reduced when HT-29 cells were previously exposed to LB95. In the cytotoxicity assays, the cell-free supernatant of the co-culture (CFSC) of VTEC with LB95 accounted for the lowest value obtained amongst the co-cultures of VTEC with LABs, and was significantly lower than the value obtained with the co-culture of VTEC with the two probiotic reference strains. The cytotoxicity of CFSC of VTEC with both LB95 and LB13 exhibited values not significantly different from the cell-free supernatant of the nonpathogenic E. coli B strain. Our results suggested that LB95 may be able to attenuate the virulence of Gram-positive and Gram-negative food-borne pathogens; together with other reported features of these strains, our data reveal their possible use in probiotic foods due to their interesting potential in preventing enteric infections in humans.