Ultrastructure of the Agent of Legionnaires’ Disease in the Human Lung

Abstract

This report confirms the gram-negative ultrastructural characteristics of the Legionnaires' disease organism by direct examination of pulmonary tissue from six confirmed cases--two from the original Philadelphia epidemic of 1976 and four from more recent sporadic cases. All microorganisms seen in all six lungs were identical ultrastructurally and were predominantely within intra-alveolar macrophages, as previously observed by light microscopy. They appeared as short, blunt rods that were clearly prokaryotic; i.e., they had diffuse electron-lucent nucleoid areas interspersed among areas of well-defined ribosomes, a pinching nonseptic division, and enclosure within a double envelope consisting of two three-layer "unit" membranes, each approximately 75 A wide. This structure, together with a pinching division, is typical of gram-negative bacteria. The Legionnaires' disease organism multiples both intracellularly and extracellularly in tissue and has no unique ultrastructural features that would aid in its specific identification. These findings are compared with recent reports describing the ultrastructure of what was considered to be the Legionnaires' disease organism in yolk sac and culture medium, and in one human lung.

Physiology and morphology of Legionella pneumophila in continuous culture at low oxygen concentration

“…Although the presence of intracellular granules has not been commented on previously by physiologists and biochemists working with legionellae, such granules have been observed in vivo by microscopists. For example, Chandler et al (1979) noted the presence of lipid granules in legionellae growing in alveolar macrophages at 37 "C. Similar observations were made for legionellae growing in yolk sac membranes (Rodgers, 1979), the protozoon Tetrahymena pyrijiormis (Fields et al, 1986) and the amoeba Acanthamoeba palestensis at 35 "C (Anand et al, 1983). By contrast, few granules were observed in legionellae growing in Acanthamoeba polyphaga at a lower temperature of 30 "C (Rowbotham, 1984).…”

“…The alterations in phospholipid composition are less easy to interpret. The reduced content of phosphatidylcholines at low temperature seems surprising, as phosphatidylcholines have a 20°C lower melting temperature than phosphatidylethanolamines with identical acyl substituents (Chapman et al, 1967;Wilkinson & Nagle, 1981). However, since this is due to packing effects and the greater ability of the ethanolamine head group to form inter-molecular hydrogen bonds, the effect is likely to be less pronounced in mixed phospholipids.…”

Collagen IV-derived peptide binds hydrophobic cavity of Legionella pneumophila Mip and interferes with bacterial epithelial transmigration

“…To improve the clinical situation, the identification of alternative bacterial targets for the development of a complementary therapy strategy remains an important goal. L. pneumophila is an intracellular pathogen of human alveolar macrophages, where it replicates efficiently to high numbers (Chandler et al ., 1979; Baskerville et al ., 1983). However, 93% of the alveolar surface is lined by lung epithelial cells, which receive structural support from the underlying basement membrane (Dunsmore and Rannels, 1996).…”

Development of the BIOLOG substrate utilization system for identification of Legionella spp

“…Many researchers have reported the presence of electron translucent granules in Legionella spp. The appearance and staining properties of these granules have led the authors of these reports to suggest that the inclusions resemble PHB granules (6,23). Our finding that L. pneumophila contained PHB provides direct evidence for PHB accumulation by legionellae (17).…”