Relationship between free amoeba and Legionella: studies in vitro and in vivo.
In 1980, Robowtham demonstrated that Legionella multiplies in free amoeba cytoplasm and hypothesized that the amoeba could act as a reservoir of virulent bacteria. In this paper we report various aspects of the relationship between amoeba and Legionella. A liquid medium co-culture method was applied to Acanthamoeba sp. and Legionella pneumophila serogroup 1. Within 4 days, Legionella growth increased by 2 log s CFU/ml. Using a direct immunofluorescence assay and electron microscopy, Legionella was shown to grow abundantly inside phagosomes, and bacteria and/or antigen were present on the cytoplasmic membrane of the amoeba. These aspects are very similar to those observed with Legionella-infected alveolar macrophages. The morphology and structure of Legionella cells were modified after 20 days of co-culture: - viable bacteria showed large fatty cytoplasmic inclusions, - gas liquid chromatography analysis demonstrated a decrease in the i16:0 fatty acid ratio. Cystic forms of amoeba were abundant but none contained viable Legionella. In an in-vivo study using a guinea-pig aerosol infection model, we compared the virulence of Legionella in co-culture with Legionella grown on charcoal dialysed yeast extract (CDYE) agar medium. The Legionella obtained by co-culture had an LD 50 (50% lethal dose) similar to that obtained for those grown on CDYE, showing that bacterial virulence is preserved in the cellular model.
Vandenesch
F
F
Centre National de Référence des Légionelloses, Laboratoire National de la Santé, Faculté de Médecine, Lyon, France.
Surgot
M
M
Bornstein
N
N
Paucod
J C
JC
Marmet
D
D
Isoard
P
P
Fleurette
J
J
D000048:Acanthamoeba / Q000502:physiology* / Q000648:ultrastructure; D000336:Aerosols; D000818:Animals; D002849:Chromatography, Gas; D003470:Culture Media; D005227:Fatty Acids / Q000032:analysis; D005455:Fluorescent Antibody Technique; D006168:Guinea Pigs; D007700:Kinetics; D007875:Legionella / Q000254:growth & development* / Q000472:pathogenicity / Q000648:ultrastructure; D007877:Legionnaires' Disease / Q000382:microbiology*; D008297:Male; D008854:Microscopy, Electron; D014774:Virulence
D000336:Aerosols; D003470:Culture Media; D005227:Fatty Acids