Antagonistic effect ofpediococcusspp. againstlisteria monocytogenes

A total of 37 strains of Pediococcus were screened for antagonistic effect against the growth of eight strains of Listeria monocvtoaenes (CA, V7, Scott A, 19111, 19113, 19115, F5027, F5069). Using an agar plate diffusion method, 28% of the 296 pairings were positive with distinct, clear zones of inhibition evident. The positive reactions were primarily seen with Pediococcus acidilactici strains isolated from or associated with meat fermentations and from abdominal related sites in humans. Strains of Pediococcus pentosaceus and Pediococcus damnosus also showed an inhibitory effect against Listeria. Studies employing growth extracts of P. acidilactici PO2 versus growth of L. monocvtoaenes 19113 showed that the inhibitory substance was retained by a molecular sieve with a pore size of 12,000 daltons, that P02 growth extract in late stationary phase (48 hour culture) was most effective, and that apparent resistant sub‐populations of L. monocytoaenes 19113 eventually arose after continued exposure to the growth extract.