VIII47-4 MANUAL OF METHODS FOR PURE CULTURE STUDY 



4) Toxin neutralization: toxin-antitoxin reactions. 



5) Hemolysis: hemolysin reactions. (See Leaflet VI, pages VI40-I6- 



18.) 

 The most frequently employed serological reactions for the identi- 

 fication of bacteria are those of agglutination and complement 

 fixation. The agglutination method is especially rapid and reliable. 

 Adequate controls on all reagents are essential for each procedure. 



DEFINITION OF TERMS 



An aniige7i is defined as a substance which, when introduced parenterally into an 

 animal body, stimulates the animal to produce specific bodies that react or unite with 

 the substance introduced. In this outline of methods the term will be limited to sus- 

 pensions of living or killed bacteria or their products. Agglutinogen, 'precipitinogen, 

 toxin, and toxoid are some of the names applied to antigens employed in the various 

 serological procedures. 



An antibody is the specific body above mentioned, produced by the animal in re- 

 sponse to the introduction of an antigen. These antibodies under the right conditions 

 may act as one of the principal factors in jireventing any injurious action which the 

 antigen might otherwise exert. For u.se in practical serology, antibodies are obtained 

 from the blood serum and appear in the globulin fraction. Agglutinin, precipitin, and 

 antitoxin are designations in common use. 



Complement is a third substance which may take part in serological reactions. It is 

 present in varying degree in the normal serum of all animals, combines with the anti- 

 gen-antibody union and may bring about lysis of the bacteria, is non-specific and is 

 not increased during immunization, and in contrast to bacterial antibodies which are 

 relatively heat stable, is inactivated by exposure at 56°C for 30 minutes and deterio- 

 rates in a few days at refrigerator temperature. 



A hapten or partial antigen is that portion of an antigen which contains the chemical 

 grouping upon which the specificity depends. The hapten reacts specifically with the 

 corresponding antibody, but by itself, when separated from the carrier molecule, is 

 incapable of stimulating the formation of antibodies in vivo. 



Heterophile antigen is the term applied to common antigens which may occur in the 

 tissues of animals which are not closely related. Several have been described of which 

 the Forssman heterophile antigen is an example. When guinea pig kidney emulsion 

 is injected into rabbits an antibody (Forssman antibody) is formed which reacts with 

 sheep erythrocytes. The Forssman antigen has been found in several species of 

 bacteria. Among bacteria, common antigens may be found in groups that are widely 

 divergent in morphological and biochemical characters. 



BACTERIAL DISSOCIATION 



Bacteria may produce variants which differ from the parent in one or more charac- 

 ters such as colony form, morphology, virulence, biochemical activity or antigenic 

 composition. Variation in serological reactivity may or may not be correlated with 

 other variation, may occur naturally or be induced, and may or may not be a stable 

 change. There is, for example, change from smooth (S) to rough (R) with intermedi- 

 ate phases, variation in motility or presence oi flagellar (H) antigens, form variation or 

 change of somatic (O) antigen, pliase variation of flagellar antigen involving change in 

 serological reactivity of motile forms. These and other variations in the antigenic con- 

 stitution of bacteria must be considered in pure culture study by serological methods, 

 and these variations arc often the explanation of anomalies observed in the results of 

 serological tests. 



AGGLUTINATION 



The antibodies in the blood scrum of immunized animals that cause 

 clumping or agglutination of bacteria are called agglutinins. Agglu- 

 tinins may occur naturally, but if present are usually weak. 



The agglutination of a suspension of bacteria by its homologous 

 immune serum may be observed either microscopically or macroscopi- 



