Effects of epiphytic Enterobacteriaceae and pseudomonads on the growth of Listeria monocytogenes in model media

Four Enterobacteriaceae (Enterobacter agglomerans and Rhanella aquatilis) a nd six pseudomonads (Pseudomonas flu orescens, Pseudomonas chlororaphis, Ps eudomonas putida) isolated from minimally processed green endive were coino culated at 10 degreesC with Listeria monocytogenes in a minimal medium. Pse udomonads did not modify the growth of L. monocytogenes, whereas Enterobact eriaceae reduced its maximal population by 2 to 3 log CFU/ml, The same effe ct was observed in a diluted yeast extract medium supplemented with amino a cids and glucose, in which L. monocytogenes grown alone reached 10(9) to 10 (10) CFU/ml. In the same diluted yeast extract medium, not supplemented wit h glucose and amino acids, the maximal population of L. monocytogenes in th e presence of both Enterobacteriaceae and pseudomonads was only slightly re duced (less than 0.5 log CFU/ml). Culture filtrates of the Enterobacteriace ae had no inhibitory activity on L, monocytogenes, The effect of the Entero bacteriaceae on L. monocytogenes growth was presumably due to a competition for glucose and/or amino acids.