688. Phage-organism relationships among strains ofStreptococcus cremoris: the selection of strains as cheese starters

Abstract

The relationships between nineteen strains of Str. cremoris and nineteen phage races were investigated. It was found that in addition to clear-cut lytic reactions there were other actions between some phage races and bacterial strains whereby in some cases a phage could show adaptation to a strain and become changed in host range, and in other cases could inhibit growth of a strain without any phage multiplication.There is some evidence to indicate that bacterial strains and phage races fall into family groups within which most of the phages act in one way or another on most of the strains. The suggestion is made that the strains and races in a group may have originated from a parent bacterial strain and parent phage race.The selection of strains of Str. cremoris for use as cheese starters is discussed in the light of the findings reported in the present paper. The diffculty of isolating a large number of strains unrelated in every respect is indicated.