Inhibition of Listeria monocytogenes in a smear-surface soft cheese by Lactobacillus plantarum WHE 92, a pediocin AcH producer

The anti-listeria monocytogenes activity of Lactobacillus plantarum WHE 92, a pediocin AcH producer, was investigated in Munster cheese, a smear-surface soft cheese. The appearance of L. monocytogenes in the cheese, which naturally occurs solely in the crust and never before 1 week of ripening, could be prevented by spraying a cell suspension of L. plantarum WHE 92 (ca. 10(5) CFU/ml) on the cheese surface at the beginning of the ripening period. 1,. monocytogenes was sometimes detected at low levels (<5.0 x 10(1) CFU/g) after 7 to 11 days of ripening. However, this pathogen was not able to grow, nor did it survive the presence of L. plantarum WHE 92 in any of the samples examined until the end of ripening (21 days), whereas it often reached counts higher than 10(4) CFU/g in control samples. In other respects, L. plantarum WHE 92, which exists naturally in Munster cheese, did not adversely affect the evolution of the ripening process. This procedure has allowed manufacturers to successfully put an antilisterial treatment into practice in their ripening rooms.