Analysis of the bacterial surface ripening flora of German and French smeared cheeses with respect to their anti-listerial potential.

The anti-listerial potential of 19 different French smeared cheese bacterial consortia was analyzed semi-quantitatively. Comparison of the total viable cell count to the direct microscopic count yielded no indication that non-culturable bacteria contribute significantly to the undefined, complex ripening floras. From 2613 isolates, 48 showed clear inhibition of one or more Listeria monocytogenes strains on solid medium, while only three isolates excreted an anti-listerial, soluble substance when grown in liquid culture. From a total of 299 strains isolated from German dairy products, 30 strains inhibited at least one L. monocytogenes indicator strain on solid medium. Bacteria with antilisterial potential were members of the genera Arthrobacter, Brevibacterium, Corynebacterium, Enterococcus, Micrococcus and Microbacterium. Cluster analysis of inhibition pattern revealed that similar anti-listerial substances are produced by species belonging to different genera. Half of the strains inhibited six or more out of 12 Listeria indicator strains and are promising candidates for the development of a defined red smear cheese ripening flora. L. monocytogenes originating from red-smear cheese had a tendency to be more resistant towards anti-listerial activity than those isolated from other sources.