< 



f 



Electron Microscopy of the Legionnaires' Disease Bacterium 







Figure 3. Electron micrograph of Legionnaires' disease bacteria witliin phagocytic vacuole (blunt arrow) of 

 degenerating alveolar inflammatory cell. Extracellular organisms are also seen (arrows) (XI 2,750). Inset: Detail 

 of dividing organism within alveolar macrophage. Note central pinching (arrows) and enclosure by a double 

 envelope (uranyl acetate and lead citrate, X61,712). 



debris and fibrin (Fig. 3). Multiplying as well as degenerating organisms are observed intracellu- 

 larly and extracellularly. We have seen fewer LD bacteria within neutrophils and, when present, 

 only one to six organisms usually occupy a phagocytic vacuole in one plane of section. 



Because the ultrastructural features of the LDB are not unique, it may be impossible to 

 differentiate this organism from other small gram-negative bacilli by fine structure alone. How- 

 ever, our studies confirm the characteristic gram-negative ultrastructure of the LDB and earlier 

 reports of its gram-negative staining when isolated from cultures. 



45 



