454 BACTERIOPHAGES 



Stability of Viruses and Selection of Diluents 



Most bacterial viruses are remarkably stable when diluted 

 in broth, serum, ascitic fluid and similar diluents, not being 

 inactivated at an appreciable rate even at 60 °C. However, 

 when diluted in salt solutions or chemically defined media, all 

 the phages are less stable and some are strikingly unstable. 

 All the coli-dysentery phages in the T system are rapidly in- 

 activated at gas-liquid interfaces when diluted in media free of 

 protein (Adams, 1948). If dilute suspensions of phages in 

 protein-free media are to be subjected to bubbling or shaking, 

 they should be protected from "surface inactivation" by addition 

 to the medium of a few ^ug./ml. of gelatin or other protein. 



The chemical nature and concentration of salts present in a 

 diluent also affect the stability of some bacterial viruses. The 

 coli-dysentery phages Tl and T5, when diluted in 0.9 per cent 

 saline, are rapidly inactivated even at room temperature. 

 However, addition to the saline of divalent cations such as 

 Mg "'"''" or Ca"^"^ at a concentration of 10~^ Af results in a striking 

 increase in stability of these phages (Adams, 1949a). 



Viruses in general, when suspended in salt solutions, are 

 subject to very rapid inactivation by small amounts of toxic sub- 

 stances such as cationic and anionic detergents (Stock and 

 Francis, 1943), oxidizing agents and heavy metals (Knight 

 and Stanley, 1944). These materials are much less effective 

 in destroying virus infectivity when the viruses are diluted in 

 broth. When viruses are to be diluted in salt solutions, the 

 most scrupulous care must be exercised to make certain that 

 glassware and solutions are free from traces of acid-dichromate, 

 detergents, heavy metals, and chlorine (which inay appear in 

 distilled water). 



Preparation of High Titer Phage Stocks 



The ability to produce a high tiler phage stock at will is 

 largely the result of considerable experience with the particular 

 phage and host cell under consideration. However, certain 

 general principles can be stated which may be of help. Strain 



