102 BACTERIOPHAGES 



papain can reactivate phage which has been treated with serum 

 under conditions minimizing the possibility of specific aggrega- 

 tion. These successful attempts to reactivate neutralized phage 

 particles indicate that antibody does not kill or destroy phage 

 particles. Presumably, it interferes with some step in the inter- 

 action of the intact virus particle with the host cell. The nature 

 of this interference will be discussed in a later section. 



From the foregoing discussion, it is clear that neutralizing 

 antibody acts on the phage particles themselves, rather than 

 on the host cell. Pretreatment of host cells with phage anti- 

 bodies has no effect on the infectious process. Delbriick 

 (1945b) found that, following phage adsorption to the host cell, 

 the infected bacteria are immune to antiphage serum through- 

 out the latent period (see, however, Lieb, 1953; Gross, 1954a; 

 Nagano and Mutai, 1954a). The resistance of infected bacteria 

 to antiphage serum is of great importance in phage technology 

 because it permits the inactivation of unadsorbed phage with- 

 out affecting the multiplication of phage which is already ad- 

 sorbed. 



Although complement is not required for specific neutraliza- 

 tion, it can modify the neutralization of Tl and T2 (Hershey 

 and Bronfenbrenner, 1952). Complement and properdin to- 

 gether, but not separately, inactivate T2 in the absence of 

 specific antibody (Van Vunakis, Barlow, and Levine, 1956). 



4. Properties of Incompletely Neutralized Phage Preparations 



Following the treatment of phage preparations with anti- 

 serum, the surviving infectious particles are not normal. An- 

 drewes and Elford (1933b) reported that the survivors of anti- 

 body treatment produced smaller plaques than normal. They 

 interpreted this as indicating a delay in the initiation of the 

 infectious process. The surviving particles also failed to pass 

 through bacteriological filters and collodion n^embranes which 

 were freely permeable to the same phage particles prior to 

 serum treatment. This might be ascribed to increase of par- 

 ticle size or change of surface charge due to an antibody coating, 



