CHAPTER IX 

 Serological Methods 



E. Edward Evans 



INTRODUCTORY 



The in vitro reactions between antigens and their homologous anti- 

 bodies have been widely used in the classification and identification of 

 microorganisms. Serological reactions may disclose marked differences 

 among cultures that appear to be similar on the basis of morphology and 

 physiology, and conversely, serological classification may bring a certain 

 order and unity to a biochemically heterogeneous collection like the 

 Klebsiella-Aerobacter group (Edwards and Ewing, 1955). 



Not only have serological methods, refined by the immunochemist, 

 been of value for extending our knowledge of microbial antigenic struc- 

 ture; they are of potential value as research tools in other areas of micro- 

 biology like genetics, metaboUsm, and cytology. A stimulating applica- 

 tion of immunological methods to the study of protein biosynthesis is 

 presented in Cohn (1952). 



The present chapter has been written primarily for those trained in 

 areas other than immunology in the hope that original applications for 

 serological methods may be found in other fields. No attempt has 

 been made to present all the fundamentals of immunology or the more 

 advanced aspects of immunochemistry. Those interested may consult 

 several good textbooks covering these disciplines. 



PREPARATION OF ANTISERUM 



Antiserum for use in the study of microbial antigens is usually prepared 

 by immunizing one of the common laboratory animals with a suspension 

 of microorganisms or with a solution of antigenic material derived from 

 them. Suspensions of intact organisms are called "vaccines," *'bacte- 

 rins," or simply ''antigens." 



Antigens. In the case of nonpathogens, immunization can be accom- 

 plished by injecting suspensions of living or killed organisms into a suit- 



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