HOST SPECIFICITY 123 



3. Host Specificity in Adsorption 



D'Herelle (1926) demonstrated that centrifugation of a mix- 

 ture of phage and host bacteria, following a brief incubation, re- 

 sulted in sedimentation of 98 per cent of the phage with the 

 bacteria. Because of the generality of this phenomenon, 

 d'Herelle concluded that adsorption is an essential first step in 

 phage multiplication. He also showed that bacteria which are 

 not able to adsorb a given phage cannot serve as hosts for its 

 multiplication. The reverse, however, is not necessarily true. 



Burnet (1927) in an extensive study of the host ranges of a 

 group of salmonella phages noted a high correlation between the 

 possession of certain heat stable agglutinogens (the O or somatic 

 antigens) and susceptibility to certain bacteriophages. Smooth 

 to rough mutation in these salmonella strains was correlated with 

 a loss of the heat stable antigens and with loss of susceptibility to 

 the phages. At the same time the bacteria acquired sensitivity 

 to a new group of phages, specific for rough salmonellas (Burnet, 

 1929b). Certain of these rough salmonella strains were able to 

 undergo the reverse mutation to smooth, simultaneously becom- 

 ing resistant to the "rough-specific" phages and reacquiring 

 susceptibility to the "smooth-specific" phages. Although the 

 correlation between antigenic structure and phage susceptibility 

 was not complete, it was evident that susceptibility or resistance 

 to certain groups of phage was dependent on the presence or ab- 

 sence of certain host cell antigens (Burnet, 1930). The suscepti- 

 bility to other phages was dependent on surface substances 

 which apparently were not agglutinogens. 



An interesting example of phage specificity is seen in the 

 typhoid phage reported by Sertic and Boulgakov (1936b) which 

 attacks H (flagellated) strains but not O (nonflagellated) strains. 

 Phage-resistant mutants are invariably nonmotile, nonflagel- 

 lated, and lacking in H-antigen. The growth of phage-suscepti- 

 ble, motile strains on agar containing phenol results in the loss of 

 flagella and confers phage resistance on the population. The 

 phage is also inhibited in typhoid strains possessing Vi antigen. 



