The Rôle of Intracellular Bacteriophage in Lysis of Susceptible Staphylococci

In a previous paper on the kinetics of the bacterium-bacteriophage reaction (1) it was shown that under certain set conditions lysis of susceptible staphylococci occurs when the total phage i.e., extracellular plus intracellular phage, present in a bacterium-bacteriophage mixture attains a value of 125 activity units (2, 3) per organism, and that lysis is not determined by the total quantity of phage per ml. of suspension. This is true both for cultures actively growing in the presence of phage and for suspensions in which resting cells are exposed to the critical number of phage units by addition of the requisite amounts of phage. In a suspension of bacteria containing phage, the phage is distributed in such a way that the concentration of phage in the bacteria is directly proportional to the concentration of phage in the surrounding solution (4). The phage is therefore partly inside and partly outside the bacterial cell and lysis may conceivably depend on any one of the following four conditions. Total phage per bacterium (P/B), external phage per bacterium (Pe/B), internal phage per bacterium (Pb/B) or external phage per ml. [Pe]. These latter two values are proportional to each other as mentioned above and therefore cannot be separated by any experiment carried out under equilibrium conditions. I t is possible however to decide whether o.r not the total phage per bacterium is the essential condition by diluting a suspension of phage and bacteria containing slightly more than the amount of phage necessary for lysis. When this is done the total phage per bacterium will evidently be constant in all 329