Ten Leuconostoc mesenteroides and one Ln. citreum strains isolated from fresh fruit and vegetables were
tested for their antagonistic capacity against Listeria monocytogenes. Genetic differences among strains were
analyzed by Random Amplified Polymorphic DNA (RAPD). All the isolates clustered together and differed
from the type strain Ln. mesenteroides ATCC 8293 as well as from Ln. fallax and Ln. citreum. Organic acids,
hydrogen peroxide and bacteriocins were detected as main inhibition mechanisms. Characterization of
culture supernatants from the bacteriocinogenic strains, CM135 and CM160 revealed a high resistance of
antibacterial activity to temperature and pH, and a bactericidal mode of action against L. monocytogenes.
Produced bacteriocins belonged to the Class IIa and sequencing of genes showed complete homology with
mesentericin Y105. A study of the effect of the relative dose of pathogen and LAB on control of L.
monocytogenes in wounds of Golden Delicious apples and Iceberg lettuce leaf cuts was performed. A
comparison of the dose of bioprotective strain needed for a ten fold reduction of the viable pathogen
concentration (ED90) revealed that strain CM160 was the most effective against L. monocytogenes. ED90 values
varied from 1.3·104 to 5.0 ·105 cfu·g−1 or wound, at ranges of pathogen levels from 1.0·103 to 5.0 ·104 cfu·g−1
of lettuce or wound of apple. The efficiency of the strains was also calculated as the ratio of the ED90 value to
the pathogen dose inoculated. The lowest ratio was found for strain CM160 at 5 to 50 cells of LAB per cell of
pathogen. The strain offers potential application for prevention of the presence of L. monocytogenes in fresh
fruit and vegetables.