Legionella spp.

  • Douglas I. Johnson


  • Genomics:
    • Legionella pneumophila chromosome: 3,397,754 bp; 2,943 predicted ORFs (Chien et al. 2004)

  • Cell morphology:
    • Thin, rod-shaped cells; appear as coccobacilli in tissue (Fig. 20.1)

    • Atypical LPS:
      • Fifteen different O-chains

      • LipidA: more hydrophobic and less endotoxic than typical LPS

    • Pili: long type IV; PilE subunits

    • Flagellum: monopolar; associated with increased virulence

  • Gram stain:
    • Gram negative

  • Growth:
    • Aerobes: catalase positive, oxidase positive

    • Prefers high temperatures: 32–45 °C

    • Requires cysteine, iron, low sodium (Na):
      • Lacks cysteine biosynthetic genes

      • Sodium (Na) sensitivity:
        • Na-sensitive cells – virulent

        • Na-resistant cells – avirulent

    • Two growth phases:
      • Replicative (intracellular) phase: nonmotile, long filamentous rods

      • Active infective (transmissive) phase: motile, short rods; monopolar flagellum

    • Normal reservoir: primarily aquatic environments; protozoans (amoeba) living in lakes and ponds:
      • Endosymbiotic relationship with freshwater amoeba (e.g., Acanthamoeba castellanii).

      • Same genes needed to grow in amoeba and human macrophage.

      • Has access to DNA from a variety of bacterial, viral, and protozoan sources – “global mobilome” (Gomez-Valero and Buchrieser 2013).

      • Has the most eukaryotic-like genes of any prokaryote; acquired through horizon gene transfer (HGT).

    • Sources of contaminated H2O: biofilm formation on piping and other abiotic surfaces:
      • Premise plumbing: tap H2O in schools, hospitals, and public and private housing

      • Cooling towers (40–60% tested)

      • Air-conditioning systems

      • Humidifiers

      • Hot tubs, spas, showers

      • Misting equipment for vegetables

    • Excellent biofilm former: abiotic and biotic surfaces (lung epithelial cells)

    • Fifty eight species with three subspecies and ~60 serotypes


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Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  • Douglas I. Johnson
    • 1
  1. 1.Department of Microbiology & Molecular GeneticsUniversity of VermontBurlingtonUSA

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