The differentiation ofStreptococcus cremorisandStreptococcus lactisby means of bacteriophage action

Abstract

1. A series of lactic streptococci which were almost all capable of clotting milk in 24 hr. at 22°C. were divided into two groups on the basis of a few simple biochemical and morphological tests. The two groups corresponded to what some workers consider to be the speciesStr.lactisandStr.cremoris.2. A series of phage races were tested for their action on the streptococci under various temperature and growth conditions.3. The characteristics of phage attack on the organisms tended to confirm the division intoStr.lactisandStr.cremorisspecies. Each of the strains of the long-chainedcremoristype was attacked by only a few phages at the most, sometimes by a single phage only, whereas each of thelactis(short-chained) strains was attacked by a variety of phages. Furthermore, with two exceptions, the phage attacking thecremoristypes on the one hand and thelactistypes on the other formed quite separate and distinct groups.4. None of the phages acted upon the several available strains ofStr.faecalisand other group D (Lancefield) streptococci.5. The evidence obtained from the phage sensitivity tests seems to justify the division of the lactic streptococci into two species,Str. lactisandStr. cremoris.The author is indebted to Dr H. R. Whitehead for his interest in this work, and for helpful criticism and advice.