Infection and Immunity, September 2001, p. 5335-5344, Vol. 69, No. 9
0019-9567/01/$04.00+0 DOI: 10.1128/IAI.69.9.5335-5344.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Infectious Diseases Laboratories, Institute of Medical and Veterinary Science, Adelaide, South Australia 5000, Australia1; Department of Microbiology-Immunology, Northwestern University Medical School, Chicago, Illinois 606112; and AstraZeneca Research and Development, Waltham, Massachusetts 024513
Received 19 January 2001/Returned for modification 14 March 2001/Accepted 22 May 2001
A guinea pig model of experimental legionellosis was established for assessment of virulence of isolates of Legionella longbeachae. The results showed that there were distinct virulence groupings of L. longbeachae serogroup 1 strains based on the severity of disease produced in this model. Statistical analysis of the animal model data suggests that Australian isolates of L. longbeachae may be inherently more virulent than non-Australian strains. Infection studies performed with U937 cells were consistent with the animal model studies and showed that isolates of this species were capable of multiplying within these phagocytic cells. Electron microscopy studies of infected lung tissue were also undertaken to determine the intracellular nature of L. longbeachae serogroup 1 infection. The data showed that phagosomes containing virulent L. longbeachae serogroup 1 appeared bloated, contained cellular debris and had an apparent rim of ribosomes while those containing avirulent L. longbeachae serogroup 1 were compact, clear and smooth.
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