An Ecological Study of Lytic Bacteriophages of Lactococcus lactis subsp, cremoris Isolated in a Cheese Plant over a Five Year Period

The development of bacteriophages lytic. or Lactococcus lactis subsp. cremoris was followed for. five years in a Danish Cheddar cheese factory, during which time the factory used the mixed Cheddar starter TK5 exclusively. All isolated lytic bacteriophages were small, isometric-headed phages; the host range, burst size and restriction endonuclease digestion pattern differed among these phages. The virulence of the phages was, in general, low. On the basis of DNA hybridization, the majority of the phages could be divided into two groups with a low degree of homology between them, but with a high degree of homology within each group. The first group consisted mainly of the phages that appeared between February 1982 and July 1984, while the second group consisted of phages isolated from January to April of 1986. The type phage P008 hybridized to the first group, while the type phage P335 hybridized to the second group. All phages from one group showed some DNA DNA homology with the phages from the other group. The results indicate that new phages appear with time and that a 'new' phage may develop in a cheese plant. from existing lytic phages or. from lysogenic strains.