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.
Centre National de Référence des Légionelloses, Laboratoire National de la Santé, Faculté de Médecine, Lyon, France.
F
F
Vandenesch
M
M
Surgot
N
N
Bornstein
J C
JC
Paucod
D
D
Marmet
P
P
Isoard
J
J
Fleurette
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