Little is known about the microbial ecology of the surface flora, which develops on smear cheeses during ripening, and which is considered to be composed of several different species of bacteria and yeasts. The growth of the yeast results in an increase in the pH of the surface layer of the cheese which, in turn, allows growth of spoilage and pathogenic bacteria, particularly, Listeria monocytogenes to occur. Such cheeses support growth of listeria and have been implicated in listeriosis. This has obvious implications for the health of consumers. Some strains of brevibacteria from the surface of smear cheese have been shown to produce bacteriocins but this only reduce the growth of listeria by 1-2 log cycles. Whether yeast also inhibit listeria has not been studied.
Very little is known about the microbial ecology of the surface flora of smear cheeses. These cheeses support growth of listeria and they have been implicated in listeriosis and death. This has obvious implications for human health. In this project we will: 1) characterise the surface microflora (both yeast and bacteria) of Limburger, Reblochon, Livarot, Tilsit and Gubbeen cheese using chemotaxonomic and molecular methods, to determine if the floras are the same or different. It is expected that several new taxa of yeast and bacteria will be described. 2) identify strains of yeast which have anti-listerial activity and which do not inhibit the growth of other bacteria in the smear, 3) show that they are useful in controlling growth of listeria in commercially made cheeses and 4) identify the inhibitor produced by the yeast.
The microflora of five European smear cheeses will be characterised. It is expected that several new species of yeast and bacteria will be described. Yeasts that inhibit the development of L. monocytogenes in commercial cheese will be identified and evaluated in commercial cheese production. Such yeasts will control the growth of listeria in the cheese and have no effect on the development of the smear bacteria. Thus, these cheeses will be safer to eat.