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ANNUAL CONFERENCE :: Abstract Library
Abstract Library
2003 Conference Abstract
| Type of Submission |
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Submission Type: |
Poster Presentation |
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Subject Category: |
Infection and Immunity |
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| Session Information |
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Presentation Date: |
May 27, 2003 |
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Abstract ID: |
D23 |
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Session: |
Poster 2 |
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Time: |
15:00 |
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| Presenting Author |
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| Other Authors |
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E. GARDUNO, Dalhousie University
S.G. BERK, Tennessee Technological University (USA)
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| Title |
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Ecological aspects of the transmission of Legionella pneumophila to humans |
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| Abstract Text |
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Legionella pneumophila (Lp) is a Gram-negative intracellular parasite of freshwater amoebae that accidentally infects humans to cause the atypical pneumonia known as Legionnaires’ Disease. Interestingly, Legionnaires’ Disease can only be acquired via exposure to Lp-laden freshwater aerosols, and human-to-human transmission has not yet been demonstrated. It is believed that intracellular growth in protozoa or the exposure to freshwater may be a requirement for predisposing Lp to infect humans. We report here that virulent Lp experiences morphological and tinctorial changes when suspended in distilled-deionized water (ddH2O), whereas salt-tolerant avirulent mutants remained largely unchanged. When suspended in ddH2O, mature differentiated forms of Lp (exclusively produced by virulent Lp upon intracellular growth) also experienced changes in morphology and protein composition (as determined by labelling with radioactive amino acids and SDS-PAGE), indicating Lp’s capability to distinguish ddH2O from the intracellular environment, and respond to it. Whether these changes are linked to an enhancement of Lp virulence towards humans remains to be determined. On the other hand, we have found that aerosolizable Lp-laden pellets can be produced by the ciliate Tetrahymena in the absence of Lp replication. Importantly, these pellets were ingested whole by murine J774 and human U937 macrophage cell lines, resulting in intracellular infection. Pellets also produced plaques on monolayers of L929 cells in standard in vitro infection assays. While the efficiency of plaque formation and electron microscopy observations suggested that the pellets (or bacteria released from them) were the cause of infection, the possibility that free (non-packed) Lp initiated the infections could not be unequivocally ruled out. The packed Lp showed an ultrastructure typical of the mature differentiated forms, suggesting that differentiation occurred concurrently to packaging in the absence of bacterial replication. In conclusion, Lp experiences unique signals and(or) biological events that are restricted to the freshwater environment and may, at least in part, explain the exclusive transmission of Lp to humans via water aerosols. |
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