Evaluation of live-culture-producing lacticin 3147 as a treatment for the control of Listeria monocytogenes on the surface of smear-ripened cheese

Abstract

A live Lactococcus lactis culture, producing the two-component broad spectrum bacteriocin lacticin 3147, was assessed for ability to inhibit the food pathogen Listeria monocytogenes on the surface of smear-ripened cheese. In initial experiments, the addition of Listeria to a lacticin 3147-containing fermentate produced with L. lactis DPC4275 (a transconjugant strain derived from L. lactis DPC3147) resulted in at least a 4 log reduction of the pathogen in 30 min. Two separate trials were performed in order to assess the most suitable method for application of the potential protective culture to smear-ripened cheese. In the initial trial, the L. lactis was sprayed onto the surface of the cheese either before or after Listeria was deliberately applied. Application of the culture following Listeria challenge, yielded up to a 1000-fold reduction of the pathogen in contrast to the pretreatment where Listeria numbers were unaffected. In a further trial, three applications of the live lacticin 3147-producing culture was used on a cheese surface containing Listeria. Listeria numbers were found to be up to 100-fold lower than in the cheese treated with L. lactis DPC4268 (control). While application of the live lacticin 3147 producer did not give complete elimination of the pathogen the results nonetheless demonstrate the potential of the bioprotectant for improving the safety of smear-ripened cheeses and particularly those that contain low level contamination with Listeria. The application of lacticin 3147 as a live-culture can serve as a bioprotectant for the control of L. monocytogenes on the surface of smear-ripened cheese.