Formation of a novel phagosome by the Legionnaires' disease bacterium (Legionella pneumophila) in human monocytes.

Abstract

Previous studies have shown that L. pneumophila multiplies intracellularly in human monocytes and alveolar macrophages within a membrane-bound cytoplasmic vacuole studded with ribosomes. In this paper, the formation of this novel vacuole is examined. After entry into monocytes, L. pneumophila resides in a membrane-bound vacuole. During the first hour after entry, vacuoles containing L. pneumophila are found surrounded by smooth vesicles fusing with or budding off from the vacuolar membrane and by mitochondria closely apposed to the vacuolar membrane. By 4 h, vacuoles are found less frequently surrounded by these cytoplasmic organelles, but now ribosomes and rough vesicles are found gathered about the vacuole. By 8 h, the ribosome-lined vacuole has formed. Erythromycin, at concentrations that completely inhibit the intracellular multiplication of L. pneumophila, has no effect on vacuole formation. Formalin-killed L. pneumophila also reside in a membrane-bound vacuole after entry into monocytes. In contrast to the situation with live L. pneumophila, cytoplasmic organelles are not found surrounding vacuoles containing formalin-killed L. pneumophila at any time after entry. Formalin-killed bacteria are rapidly digested, and by 4 h, few remain intact. The L. pneumophila-containing vacuole has certain features in common with other intracellular organisms that inhibit phagosome-lysosome fusion; these organisms may share a common mechanism for vacuole formation and inhibition of phagosome-lysosome fusion.

FliA expression analysis and influence of the regulatory proteins RpoN, FleQ and FliA on virulence and in vivo fitness in Legionella pneumophila

“…After inhalation of L. pneumophila by immunocompromised humans, bacteria survive and replicate within alveolar macrophages (Horwitz and Silverstein 1980). Within the host cell, the bacteria establish a specialized Legionella-containing vacuole (LCV) in which L. pneumophila starts to replicate (Horwitz 1983;Horwitz and Maxfield 1984;Sturgill-Koszycki and Swanson 2000). Finally, in the late replicative phase, when the LCV merges with lysosomes and nutrients become limiting, the bacteria enter the transmissive phase of the biphasic life cycle.…”

Legionella pneumophila inhibits acidification of its phagosome in human monocytes.

“…Bacteria: L. pneumophila, Philadelphia 1 strain, was grown in embryonated hens' eggs, then passed one time only on modified charcoal yeast extract agar for 80 h, harvested, suspended in egg yolk buffer, and counted in a Petroffhausser chamber (Arthur H. Thomas Co., Philadelphia, PA) as described (4). These bacteria were 75-100% viable as determined by measuring the number of colony-forming units in the bacterial suspension.…”

Legionella oakridgensis ATCC 33761 genome sequence and phenotypic characterization reveals its replication capacity in amoebae

“…2F, arrows), indicating that organelle recruitment to the LCV is also present in host cells infected by L. oakridgensis. The recruitment of organelles to the LCV is a phenotype which depends on a functional Dot/Icm secretion system, and is a prerequisite for intracellular replication (Horwitz, 1983;Marra et al, 1992;Berger et al, 1993;Sadosky et al, 1993;Kagan et al, 2002). The observed recruitment of mitochondria in U937 cells has also been reported by using Vero cells as host cells (Ogawa et al, 2001, Takekawa et al, 2012.…”