Antagonistic effect ofLactobacillusstrains againstEscherichia coliandListeria monocytogenesin milk

Abstract

The current work studied four types of binary antagonist/pathogen bacterial culture system, in order to determine the effect of interaction between two strains ofLactobacillus plantarumand two food-borne pathogens,Listeria monocytogenesandEscherichia coli, in whole UHT milk at 37°C. To determine the type of interaction between the two bacterial populations in co-cultures and to evaluate the antagonistic activity of the lactic acid bacteria (LAB) on the pathogenic bacteria, the growth curves, the kinetic parameters, and the pH profiles of mono- and co-cultures were compared. TheLb. plantarumstrains showed different bacteriocin-like inhibitory substance (BLIS) production, auto- and co-inducible. The antibacterial effect of neutralized supernatants of mono and co-cultures harvested at different times of incubation was assessed in order to establish the presence of bacteriocin-like inhibitory-substances (BLIS) and their possible relation to the growth inhibition of the pathogen. The LAB reduced the growth ofEsch. coliand ofList. monocytogenesby 4 and ∼5 log cycles, respectively and influenced other growth kinetic parameters, such as μmaxand lag phase, in the different binary combinations. The growth of the LAB was not relevantly altered by simultaneous growth with the pathogenic strains showing an interaction of amensalism. The pattern of inhibition exerted by the LAB on the pathogens was different;Lb. plantarumLB279 inhibited the growth ofList. monocytogenesmore effectively than that ofEsch. coli. The behaviour ofEsch. coliin co-culture withLb. plantarumWS4174 suggested the presence of metabolic crowding in the mechanism of growth suppression. This exploratory study showed the complexity and specific particularities of the inhibition phenomena between bacterial communities.