1 56 BACTERIOPHAGES 



Similar observations were made by Goebel (1950) using phage 

 T3 and the purified somatic antigen of phase II Sh. sonnei. 

 Phage T3 was rather slowly inactivated by the somatic antigen 

 and a residue of the population, about 1 in 10^, proved to be 

 completely resistant to inactivation. The original T3 phage 

 population plated with equal efficiency on E. coli strain B and on 

 Sh. sonnei, phase II. However, the PIA-resistant survivors 

 showed a 40 times greater plaque count on E. coli than on Sh. 

 sonnei. PIA-resistance and the property of plating only on E. 

 coli were not hereditary. 



There are many references to qualitative observations on the 

 phage-inhibiting activities of bacterial extracts among which are 

 Freeman (1937), Rountree (1947b), Beumer (1947, 1953), 

 Weidel (1953a, b), and Mondolfo and Hounie (1948). 



There have not been many experimental studies of the 

 physical and chemical properties of the phage-inhibiting agents 

 of bacterial extracts. Gough and Burnet (1934) reported on the 

 properties of PIA isolated from Sh. fiexneri. The material was 

 soluble in half-saturated ammonium sulfate but was precipitated 

 by saturated ammonium sulfate, and by 2.5 volumes of alcohol. 

 Material repeatedly precipitated by these agents was active 

 serologically and as PIA. It gave a strong Molisch test for 

 carbohydrate, a weak biuret test, and no pentose color reaction. 

 Treatment with hot one per cent NaOH liberated the poly- 

 saccharide hapten which was serologically active but had no 

 phage-inhibiting activity. Heat treatment at 90° C. and pH 9 

 caused a rapid loss of PIA with no change in serological activity. 

 The inhibitory activity toward different phages was lost at 

 widely different rates suggesting that not all phages reacted with 

 the same part of the PIA. Attempts at further purification in- 

 variably resulted in decreased PIA activity. 



Meanwhile a great deal of chemical work on the somatic anti- 

 gens of the enteric pathogens demonstrated that these antigens 

 are not simple polysaccharides, but are, rather, a complex as- 

 sociation of polysaccharide, phospholipid, and protein. The 

 phospholipid can be separated by use of polar solvents without 



