380 Microbes and You 



lives as a result of infections with the typhus fever organisms during 

 the course of their studies. Rocha-Lima contracted the disease but 

 he was fortunate enough to recover. Since these pioneer dis- 

 coveries, other rickettsial diseases have been demonstrated, and 

 they will be discussed as the chapter progresses. 



CHARACTERISTICS OF RICKETTSIAE 



MORPHOLOGY 



Bergey's Manual of Determinative Bacteriologij ( 1948 ) describes 

 rickettsiae as "small, rod-shaped, coccoid, spherical, and irregularly- 

 shaped microorganisms which stain lightly with aniline dyes. 

 Gram negative. Usually not filterable. Cultivated outside of the 

 body, if at all, only in living tissue, embryonated eggs, or rarely 

 in media containing body fluids. Parasitic organisms intimately 

 associated with tissue cells and erythrocytes, chiefly in vertebrates 

 and often in arthropods which act as vectors .... May cause 

 diseases in man or animals, or both." 



These microbes are non-motile and range in size from about 

 0.3 fx in diameter to as much as 2.0 fx in length, although 0.5 /x is 

 more common for the length. With the exception of the rickett- 

 siae causing "Q" fever, none of these organisms is filterable. That 

 is, they are retained by the types of filters usually employed to 

 hold back bacterial cells. When stained with Giemsa's stain 

 rickettsiae appear as lavender, blue, or purple-stained bodies, and 

 when Macchiavello's staining technic is employed, the basic fuchsin 

 colors the rickettsiae red and the background material retains the 

 color of the methylene blue. 



CULTURAL REQUIREMENTS 



These minute organisms have not been grown in a cell-free 

 medium, but in contrast to viruses which require young, actively 

 growing cells for their development, rickettsiae prefer older, slowly 

 metabolizing cells for their cultivation. Some investigators believe 

 that rickettsiae are forms of bacteria which have adapted them- 

 selves to intracellular life. 



