CHAPTER X 

 The Detection of Bacterial Pathogenicity 



Joel Warren 



INTRODUCTION 



The determination of bacterial pathogenicity for animals requires not 

 only a knowledge of those factors which contribute to microbial virulence 

 but skill in the technical procedures of inoculation, autopsy, and bacterio- 

 logical examination. In recent years there has been a diminished interest 

 in pathogenic studies in animals, and with a few exceptions, they are no 

 longer required in routine diagnostic bacteriology. The use of selective 

 and enriched media and the advent of antibiotics have made nearly 

 extinct such formerly routine procedures as pneumococcus typing by 

 mouse intraperitoneal inoculation or guinea-pig toxicity tests for diph- 

 theria. On the other hand, certain diagnostic procedures still depend 

 upon pathogenicity determinations, e.g., in tuberculosis, and will prob- 

 ably continue in use. In research bacteriology, especially medical and 

 veterinary, the mouse, rabbit, and guinea pig are widely employed for 

 studies of natural or induced bacterial infection, and these reports com- 

 prise a large segment of the literature. 



The section which follows is designed to provide only an introduction to 

 the study of bacterial pathogenicity. For more specific information the 

 reader should consult the literature on a particular microorganism or one 

 of the standard bacteriological texts such as Topley and Wilson (1946) or 

 Dubos (1948). For good diagrams of animal anatomy and inoculation 

 sites, see Haudauroy (1948). 



In a general sense, pathogenic bacteria are those capable of causing the 

 death of an animal when they reach a site which permits their multi- 

 plication. Bacteria which may multiply but do not cause fatal disease 

 (as, for example, Leuconostoc mesenteroides) are eliminated by this defini- 

 tion, since illness alone is generally difficult to establish in the smaller 

 animals. Thus, from a pragmatic point of view this chapter is primarily 

 concerned with those organisms which, when introduced into a host, will 



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