LEAFLET VIII 



SEROLOGICAL METHODS 

 THE USE OF SEROLOGY IN PURE CULTURE STUDY 



In the study of bacteria the facts that may be estabhshed with 

 the agency of serological reactions often have peculiar value, not 

 as substitutes for those to be gained from morphological, cultural, 

 or biochemical means, but as supplemental to them. This is espe- 

 cially true in so-called "pure culture" investigations. Thus, serologi- 

 cal studies may show that a group of organisms, apparently alike 

 morphologically and physiologically, in reality consists of different 

 sub-groups, which cannot be distinguished by other means. This 

 leaflet is intended to make readily available such serological pro- 

 cedures as are useful in pure culture studies. No implication is 

 made that these procedures are necessarily the best among the great 

 variety of serological methods now in use. They have, however, 

 proved practical in pure culture studies, and they are given herewith 

 the hope that they will be helpful to users of this Manual. 



The field designated "serology," as applied to pure culture study 

 of bacteria, deals with the reactions of the blood sera of animals 

 that have been injected with micro-organisms or their products. 

 Such substances, acting as antigens when injected into an animal, 

 stimulate the appearance of antibodies in its blood serum. This 

 serum when mixed with suspensions of unknown bacteria or their 

 products, gives a positive reaction only if the bacteria or their pro- 

 ducts are of the same type as those introduced or else are related 

 to them. This specificity is not absolute but may vary within certain 

 limits both quantitatively and qualitatively. It is often possible, how- 

 ever, by means of these relatively specific reactions to identify an 

 unknown organism, to group or sub-group closely allied forms, and 

 to study the relationship between the groups, sub-groups, and 

 strains. Divisions so established may or may not agree with previous 

 groupings based upon morphological, cultural or biochemical obser- 

 vations. As a rule the methods will be found supplemental to each 

 other and more often than not their results will coincide. Frequently, 

 when other procedures fail to show differences, serological reactions 

 will reveal them and varieties of a given species may be differentiated 

 by their antigenic properties. 



Immune sera can yield information in two ways: either a known 

 serum may be employed as the test agent for determining an unknown 

 antigen; or a known antigen may be used as a test agent to denote 

 the presence or absence of a specific antibody. Serological pro- 

 cedures that may be useful in the identification of pure cultures are: 



1) Agglutination: agglutinogen (antigen) -agglutinin reactions; ag- 



glutinin absorptions. 



2) Precipitation: precipitinogen (antigen)-precipitin reactions. 



3) Complement fixation : antigen-antibody-complement-hemolysin- 



RBC reactions. 



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