Further Studies on the Mechanism of Transmissible Lysis of Bacteria. 20

Abstract

Observing carefully the progress of lysis under the microscope we noticed that disappearance of individual bacteria under the influence of phage is usually preceded by more or less marked swelling of the cells. 1 A more detailed inquiry indicated that the swelling itself was due to imbibition of water which in turn appeared to be the result of intracellular digestion of bacterial cytoplasm, 2 and consequent increase of osmotic pressure within the cells. The actual disappearance of cells from the field was therefore interpreted as due to bursting. 3 We found further that if bacteria are grown on media in which free water was immobilized by the addition to the medium of hydrophilic colloids, the swelling was prevented and consequently lysis did not occur. On the contrary, in place of a marked fall in the number of bacteria (as would be the case if lysis had occurred), we observed actual increase in the number of bacteria when compared with control cultures grown on the same medium but in the absence of phage. 4 While the above observations were made with Gram-positive and Gram-negative bacteria, the changes were always more constant and more marked in the latter and therefore Gram-negative bacteria were used to illustrate the phenomenon. 5 Recently there appeared a paper in which the authors, 6 working with cultures of Staphylococcus, failed to observe either the swelling or the increased rate of growth of these organisms in the presence of phage. It was imperative to reinvestigate the subject.

The experiments here reported were performed to show that phenomena observed by us during the growth of Gram-negative bacteria in the presence of phage occur also with Gram-positive bacteria.