Elcctrdn Microscopy of the LcL'ionnaires" Disease Bacterium 



Figure 2. Whole preparation of Legionnaires' disease bacteria grown on bacteriologic medium. Note dividing 

 organism (arrows indicate region of central pinching) and delineation of outer envelope (blunt arrows) (uranyl 

 acetate. X43. 700). 



which appear to be extensions from the inner envelope are seen in the LDB cytoplasm. However, 

 membranous inclusions or other organelles, such as those seen in some gram-positive bacteria 

 (9), are not found in the LDB. 



Autopsy specimens from patients with LD included lung tissues obtained diu-ing the 1976 

 Philadelphia outbreak as well as those from patients associated with sporadic or epidemic cases 

 of LD since then. A confirmed diagnosis of LD was based either on results of indirect immuno- 

 fluorescent serodiagnosis, direct immunofluorescence of lung sections or smears, isolation on 

 artificial media, guinea pig inoculation, or some combination of the four as described elsewhere 

 in this manual. The electron microscopic features of the LDB in areas of typical pulmonary 

 consolidation, determined by light microscopy of hematoxylin-eosin and Dieterle silver impregna- 

 tion stained sections ( J .2), are consistent. However, the concentration of organisms varies from 

 specimen to specimen and case to case. The LDB is predominately found in phagosomes of 

 degenerating or necrotic alveolar macrophages (Fig. 3). Enormous phagosomes, which occupy 

 most of the host cell cytoplasm, may contain as many as 40 organisms in a single plane of section. 

 Extracellular LD bacteria may also be present and are often intimately associated with cellular 



44 



