690 



SHIGELLA 



Flexner V. 

 Fig. 144 



FlejtnerVJ. FlexnerX. Flexner Z. Flexner Y. 



Diagram representing the Variation in Antigenic 

 Structure of Shigella fiexneri. 

 (After Andrewes.) 



1938) in India. Studying a strain of dysentery bacillus known as 103, which 

 was biochemically similar to Flexner's bacillus, but which, when newly isolated, 

 was not agglutinated by antisera to the V, W, Y, and Z races, and only very 

 feebly by an X antiserum, Boyd observed that after some time in artificial culture 

 it gave rise to two types of colony. One of them, referred to as 103A, was in 

 all respects identical with the smooth circular colonies of the freshly isolated 

 strain, and was virtually inagglutinable by V to Z antisera. The other, referred to 

 as 103B, was slightly larger than normal and somewhat rough in outline, and 

 was agglutinated readily by antisera of the V to Z group. This variant differed 

 further from 103A in that it bred true, whereas 103A behaved like the parent 

 strain in consistently giving rise to a variant of the 103B type. Further study 

 showed that a serum prepared against 103A agglutinated both 103A and 103B, 

 but that a serum prepared against 103B had practically no action on 103A. Absorp- 

 tion of agglutinin experiments confirmed the suggestion that 103A contained 

 two antigens — a type and a group — but that 103B contained only the group 

 antigen. Since 103B grew uniformly in broth and was perfectly stable in saline, 

 Boyd concluded that the variation he had observed was more of the phasic than 

 of the smooth-rough order. It differed from the type-group variation seen in the 

 flagellar antigens of organisms of the Salmonella genus in that it was irreversible. 

 The time at which the A — > B variation occurs varies greatly from strain to strain. 

 Sometimes the parent culture may remain stable for mouths or years ; at others it 

 throws off B variants on first subculture or even in the body. 



Similar observations were made with other strains of Flexner's bacillus, such 

 as PI 19 and the 88 strain of the Newcastle-Manchester bacillus. Absorption of 

 agglutinin experiments seemed to show that the V, W, and Z races each contained 



a specific and a group antigen. The Y race 

 contained group antigen only. The group 

 antigen was not completely homogeneous ; 

 in fact Boyd obtained evidence of at least 

 six different components. The X race was 

 at first thought to be similar to the others, 

 but later Boyd (1940) came to regard it not 

 as a separate race but as an incomplete 

 variant of Z. It will be seen that in con- 

 tradistinction to Andrewes and Inman who 

 regarded V, W, X, and Z as each containing 

 the same four antigens, one of which alone 

 was dominant in each race, Boyd believes 

 that V, W, and Z share some components of 

 a common group antigen but that their 

 specific antigens are distinct (Fig. 145). On 



Fig. 145.— Diagram representing the 

 Variation in Antigenic Structure 

 OF Shigella flexneri. 



The different components of the com- 

 posite group antigen has been omitted 

 for the sake of simplicity. 

 (After Boyd.) 



