Influence of Background Microflora on Listeria monocytogenes on Minimally Processed Fresh Broad-Leaved Endive ( Cichorium endivia var. latifolia )

Interactions between Listeria monocytogenes and the background microflora of endive leaves was studied by (i) testing the effect of disinfecting endive leaves on the fate of L. monocytogenes , and (ii) challenging L. monocytogenes along with each of 10 strains of pseudomonads and Enterobacteriaceae isolated from endive leaves on both leaves of endive and in a model sterile medium based on an exudate of endive leaf. There was a higher increase in the population of L. monocytogenes on endive leaves with a background microflora reduced by a chemical disinfection. High numbers (10⁶ to 10⁷ CFU/g) of some strains reduced the growth of L. monocytogenes on endive. None of the 10 strains tested promoted the growth of L. monocytogenes . In the medium made of endive leaf exudate, the 10 strains tested reduced the maximum growth of L. monocytogenes to extents that varied with the strains. A complex bacterial population extracted from endive leaves completely inhibited the growth of L. monocytogenes in the medium.