Behaviour of Listeria monocytogenes during the maturation of naturally and artificially contaminated salami: effect of lactic-acid bacteria starter cultures.

The antimicrobial activity of a bacteriocin-producing Lactobacillus plantarum MCS strain against Listeria monocytogenes in naturally and artificially contaminated salami was evaluated in comparison with that of other non bacteriocin-producing lactic-acid bacteria (i.e., L. plantarum MCS1 mutant strain and two commercial starter cultures). In salami not inoculated with lactic-acid bacteria, moderate L. monocytogenes growth was observed after 7-14 days. The addition of the starter cultures prevented growth, but not always the survival of Listeria. During the maturation of artificially-contaminated salami, Listeria counts tended 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 Listeria (recovered by enrichment) were observed in the batches inoculated with the different lactic-acid bacteria: Listeria appeared to be absent only in salami inoculated with the L. plantarum MCS strain.