No abstract

Lysis from without (LFW) occurs in two steps: (1) sensitization of cells by phage, which renders the cells susceptible to (2) destruction of an essential cell structure by an extracellular lytic enzyme. Virolysin, from phage-infected cells, was used in these studies. Normal cell autolysin is also effective.Evidence is presented that: 1. Neither phage nor lysin alone causes LFW. 2. Sensitization requires phage adsorption. 3. It can be caused by non-infectious particles. This establishes a new biological activity of the particle.4. Heat, U.V., detergents, penicillin, and other damaging agents also sensitize cells. 5. Sensitization involves a non-lethal, reversible reaction. 6. Sensitization by phage prevents vires synthesis. Following adsorption, a cell can undergo sensitization or infection but not simultaneously. When only a few particles are adsorbed, infection can occur; when sufficient particles are adsorbed, sensitization takes place.7. Quantitative aspects of LFW are described. Lysis proceeds logarithmically. The lysis end-point depends upon the phage concentration but is independent of the enzyme concentration.

SUMMARYThe formation and role of enzyme, virolysin, in StaphyZococcus aureus K, infected with phages P, and PI, are described. Virolysin is a by-product of the metabolism of the cell which is actively producing phage, not of the normal cell. Virolysin is first detected within 10-15 min. in a 40-50min. latent period and increases linearly until lysis. Normal cell autolysin remains constant during infection. Observations on lysis and phage release show that (1) certain inhibitors which prevent lysis of the cocci by external virolysin also prevent lysis and phage release when added at the end of the latent period; (2) the rate of premature lysis of, and phage release from, cocci chilled during the latent period depends upon their virolysin content. Both observations suggest that virolysin functions in phage release.

A series of phage P1 variants was isolated from plaques developing on S. aureus WF 145. One in particular, phage 14, was studied in detail because its host range appeared to be dependent on the previous host of production; i.e., it was subject to a host control. When this phage was produced on host K1 its lysate assayed equally well on both 145 and K1 cells. When produced on host 145, however, it assayed manyfold higher on 145 than on host K1. All its particles adsorbed on K1 cells, but only a small percentage were able to produce plaques. No differences could be found in adsorption rates, latent periods, or burst sizes of the phage on the two hosts. No extracellular inactivating substances could be detected which could account for such changes, nor could the results be explained readily on a mutational basis, since distinct phage strains could not be isolated. The change in virus properties was found to occur in the first burst of singly infected host 145 cells, regardless of the previous host or its prior lytic abilities. Heat inactivation destroyed activity for K1 cells more rapidly than for 145 cells. This was found to be a property of both the stock phage P1 and phage 14. Phage 14 could be heated until there remained particles which could multiply only on strain 145. When the plaques of such survivors were examined they were found to contain phage which could multiply on both hosts in a ratio characteristic of the original unheated preparation. The data suggest that the observed changes were caused by a host control over the formation of a phage material(s) necessary for successful infection of host K1. Such a substance theoretically could be related to the labile material destroyed by heat and required for plaque formation on host K1.

By simultaneously titrating phage on two susceptible hosts, the authors have been able to detect and isolate variants from a stock staphylococcus phage PI. The dual host assay system has provided a sensitive means of studying certain unusual activities of one of the phage variants.Experimental procedures and results. I. Isolation of phage variants from stock PI.When aliquots of stock P1, prepared on host strain Staphylococcus K1 in tryptose-phosphate both, were titrated by plaque count( 1) on two hosts-strains K1 and WF 1 4 5 L a slightly but consistently higher titration value was found with the latter. This difference could not be ascribed to rates of adsorption, latent periods, or burst sizes of the pbage for the two hosts. Stock phage P1 was then produced on strain 145 in trypticase soy broth. At intervals aliquot samples were titrated on the two hosts. The ratio of titer per ml on 145 to titer per ml on strain Kl (hereafter designated 145/K1) was found to incre>ase to approximately 4 during the growth period of