SYLLABUS 107 



The serological specificity of a given strain of a bacteriophage is 

 retained by it on whatever bacterial strain it has propagated. This 

 specificity is not related to the host range activity of the bacteriophages. 

 Strains of phages active on the same bacterium may belong to very 

 different serological groups. For instance, the seven phages of the T 

 series, all active on E. coli, strain B, have been shown to belong to 

 four serological groups (see Table I, p. 147). Phages of the same group 

 cross-react with a serum prepared against any one of them. The titer of 

 such a serum is generally 5 to 100 times lower when tested with an 

 heterologous strain than with the homologous one. 



The serological classification of phages has proved to be the only 

 significant one (Burnet et al., 1937; Delbriick, 1946). Phages which 

 belong to the same serological class are generally closely related as far 

 as size, shape, and other morphological characters are concerned (cf. 

 taxonomy). Mutations involving changes in plaque size, host range, 

 etc., are well-knownn (cf. mutants), but no mutant of a given strain of 

 bacteriophage has been found involving any detectable modifications 

 in antigenic properties. 



Phage anti-phage reactions. — In a mixture of virus and antiserum, 

 the fraction of active virus decreases exponentially with time in many 

 but not in all cases (Andrewes and Elford, 1933; Hershey, 1943)- 

 The rate of inactivation is proportional to the concentration of the 

 serum. 



The rate constant of inactivation is a characteristic of the activity 

 of a given antiserum against a given phage. A good antiserum will 

 inactivate 99% of a phage suspension in one minute at a dilution i: 100. 



The combination of antibody with phage is irreversible in the 

 sense that the complex is not dissociated upon dilution. The activity 

 of neutralized phage, however, appears to be recoverable by treatment 

 of the complex with papain (Kalmanson and Bronfenbrenner, 1943)- 

 Serum inactivated T3 can also be recovered by treatment with sonic 

 vibrations (Doermann and Anderson, 1950, unpublished). 



It has been shown that a bacteriophage particle is able to adsorb 

 up to 5,000 molecules of antibody, but an adsorption of an average of 

 90 molecules is sufficient to suppress reproduction of the virus. Since 

 the inactivation curve is approximately a one-hit curve one has to 

 imagine that of the 90 antibody molecules adsorbed at the time of in- 

 activation only one or two are adsorbed to really crucial spots on the 

 phage. Just barely neutralized particles are still able to adsorb onto 



