BACTERIOPHAGES INFECTING DAIRY PROPIONIBACTERIA

Nineteen bacteriophages infecting P freudenreichii have been isolated from 32 Swiss-type cheeses. They all present a similar morphology and belong to the B1 group of Bradley's classification. According to their restriction patterns, obtained with the endonuclease Pstl, they can b e grouped into 3 clusters, 1 of which contains the majority of the pha ges. Sixteen of the 32 cheeses studied were infected with bacteriophag es. We observed that all the cheeses made from raw milk and ripened in a warm curing room for several weeks which are known to contain high concentrations of propionibacteria, were infected with bacteriophages. Moreover, the multiplication of bacteriophages occurred in cheese dur ing the multiplication stage of propionibacteria in a warm curing room . We have shown that raw milk contains bacteriophages and thus it can be a source of phages in facto:ies. However, these bacteriophages are sensitive to the milk heat treatment used for cheesemaking.