BEHAVIOR OF LISTERIA-MONOCYTOGENES DURING THE MATURATION OF NATURALLYAND ARTIFICIALLY CONTAMINATED SALAMI - EFFECT OF LACTIC-ACID BACTERIASTARTER CULTURES

The antimicrobial activity of a bacteriocin-producing Lactobacillus pl antarum MCS strain against Listeria monocytogenes in naturally and art ificially contaminated salami was evaluated in comparison with that of other non bacteriocin-producing lactic-acid bacteria (i.e., L. planta rum MCS1 mutant strain and two commercial starter cultures). In salami not inoculated with lactic-acid bacteria, moderate L. monocytogenes g rowth was observed after 7-14 days. The addition of the starter cultur es prevented growth, but not always the survival of Listeria. During t he maturation of artificially-contaminated salami, Listeria counts ten ded to decrease, but no significant differences were observed between samples inoculated with L. plantarum MCS or with the MCS1 bacteriocin- negative mutant strain. However, at the end of the maturation period, in naturally-contaminated salami, differences in the survival of Liste ria (recovered by enrichment) were observed in the batches inoculated with the different lactic-acid bacteria: Listeria appeared to be absen t only in salami inoculated with the L. plantarum MCS strain.