The ultrastructural morphologic features of Pittsburgh pneumonia agent.

The fine structure of "Pittsburgh Pneumonia Agent" (PPA) was studied in infected human lung, guinea pig omentum, yolk sac membrane, Vero cell culture, and after cultivation of the organism on buffered charcoal yeast extract agar. The organism is a prokaryotic cell with the general features of a gram-negative bacillus. PPA is ultrastructurally distinctive because of an unusually thick, electron-dense band present within the periplasmic space adjacent to the outer membrane of the cell wall. This band, presumably a mucopeptide (peptidoglycan) layer, was seen in about 95% of organisms in human lung but less frequently under certain conditions of laboratory infection or cultivation. Future studies are required to determine whether this ultrastructural dimorphism of PPA is related to variation in other properties of this bacterium, eg, gram-variability, acid-fastness, colony morphology, and virulence.