Pathogenicity of Legionella pneumophila

Nicholas P Cianciotto*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

108 Scopus citations


The bacterium Legionella pneumophila is the principal etiologic agent of Legionnaires' disease, a form of lobar pneumonia. Ubiquitous in aquatic environments, the gram-negative Legionella organism is a facultative, intracellular parasite of protozoa. The pathogenesis of legionellosis is largely due to the ability of L. pneumophila to invade and grow within alveolar macrophages, and it is widely believed that this ability results from a prior adaptation to intracellular niches in nature. Indeed, intracellular legionellae display a remarkable capacity to avoid endosomal and lysosomal bactericidal activities and to establish a unique replicative phagosome. In recent years, much progress has been made toward identifying the bacterial factors that promote intracellular infectionand virulence. Surface structures that enhance infection include LPS, flagella, type IV pili, an outer membrane porin, and the Mip propyl-proline isomerase. Both type II and type IV protein secretion systems are critical for L. pneumophila pathogenesis. Whereas the type II (Lsp) system secretes a collection of degradative enzymes, the type IV (Dot/Icm) system likely exports effector proteins that are especially critical for trafficking of the Legionella phagosome. In addition to facilitating pilus formation and type II secretion, the inner membrane prepilin peptidase (PilD) of L. pneumophila appears to mediate a third, potentially novel pathway that is operative in the mammalian host. Periplasmic and cytosolic infectivity determinants include a catalase-peroxidase and the HtrA and Hsp60 stress-response proteins. The stationary phase response and the iron acquisition functions of L. pneumophila also play key roles in pathogenesis, as do a number of other loci, including the pts, mil and enh genes.

Original languageEnglish (US)
Pages (from-to)331-343
Number of pages13
JournalInternational Journal of Medical Microbiology
Issue number5
StatePublished - Jan 1 2001


  • Intracellular parasitism
  • Legionella pneumophila
  • Legionnaires' disease
  • Macrophages
  • Type II and type IV protein secretion

ASJC Scopus subject areas

  • Microbiology
  • Microbiology (medical)
  • Infectious Diseases


Dive into the research topics of 'Pathogenicity of Legionella pneumophila'. Together they form a unique fingerprint.

Cite this