692 SHIGELLA 



It is now known that some strains of the Flexner Y variety contain somatic antigens 

 that are found in the Salmonella group. The presence of the vi.xiii combination has been 

 demonstrated by Bornstein, Saphra and Daniels (1941), who point out that care must 

 be taken in the identification of strains on the basis of agglutination. 



The antigenic structure of Sh. alkalescens is still in doubt. According to Neter 

 (1938) and Neter and Heide (1940), it contains two antigenic components, one 

 specific and the other shared with the Flexner bacillus. De Assis (19396) found 

 that two serological types could be established, distinguished by their specific 

 antigens, but that both shared the same group antigen with Sh. flexneri. Archer 

 (1942) noticed that Sh. alkalescens might form two types of colony ; against a dark 

 ground one appeared clear, the other opaque. Clear colonies were readily 

 agglutinated ; opaque colonies were hypoagglutinable, but were rendered almost 

 completely agglutinable by boiling. Boyd (1938) observed the occurrence of 

 cross-agglutination between Sh. alkalescens and an organism known as P274, which 

 was biochemically similar to Flexner's bacillus, but was not antigenically related 

 to it. Rothstadt, Fenner and Baker (1942) in Australia have brought strong 

 evidence to show that P274 is capable of giving rise to dysentery, and have suggested 

 that it should be classified with the Boyd variety. These results are conflicting. 

 On the one hand, there are observations pointing to the possession by Sh. alkalescens 

 of the group Flexner antigen and on the other to its relationship to the P274 

 type. From a study of this organism Stuart, Rustigian, Zimmerman and Corri- 

 gan (1943) conclude that there is a species-specific antigen A, a major antigen 

 B found also in paracolon and coliform bacilli, a minor antigen C found in Sh. 

 flexneri and in paracolon and coliform bacilli, and minor antigens D and E found 

 again in paracolon and coliform bacilli. These workers observed a series of 

 strains showing biochemical reactions ranging from those of the typical Sh. 

 alkalescens on the one hand to those of Bact. coU on the other, and their results 

 render it doubtful how far Sh. alkalescens can as yet be defined as a species. An 

 antigenic relationship between Sh. alkalescens and some paracolon bacilli was also 

 noted by Sevitt (1945). 



Soime's bacillus presents less difficulty. As has been mentioned, this organism 

 forms two types of colony which, as Large (1929) showed, are serologically distinct. 

 A serum prepared against organisms in the smooth colony phase agglutinates both 

 the smooth and the rough colony organisms, whereas a serum prepared against 

 organisms in the rough colony phase agglutinates only the rough colony organisms. 

 There is a close analogy with the 103 strain of Flexner's bacillus. For practical 

 identification of the organism it is important that a serum should be used con- 

 taining both types of agglutinins. Sh. dispar is antigenically heterogeneous, 

 though Carpenter (1944) found that 38 out of 44 strains he studied fell into one 



type. 



It may be noted that the agglutination of dysentery bacilli occurs rather slowly, 

 and that it is advisable to incubate all tests for 4-6 hours at 50° C, and to delay 

 the final reading till the tubes have been left at room temperature overnight. This 

 holds particularly for the newcastle, alkalescens, sonnei, and dispar types. 



Apart from the serological differentiation of the dysentery bacilli, certain indirect 

 tests may be used to distinguish between the types, such as Michaelis's (1917) 

 acid agglutination test, and susceptibility to action of the bacteriophage. The acid 

 agglutination test depends on the different H-ion concentrations necessary for 

 flocculation. Using the particular range employed by Michaelis, Andrewes and 



