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In vitro cellular toxicity predicts Pseudomonas aeruginosa virulence in lung infections
1Departments of Anesthesia and Medicine, Cardiovascular Research Institute, The University of California, San Francisco, California 94143, USA.
Abstract:
The role of quorum sensing by Pseudomonas aeruginosa in producing cytotoxicity has not been fully investigated. Strains of P. aeruginosa have been characterized as having an invasive or a cytotoxic phenotype (S. M. J. Fleiszig et al., Infect. Immun. 65:579-586, 1997). We noted that the application of a large inoculum of the invasive strain 6294 caused cytotoxicity of cultured epithelial cells. To investigate this dose-related cytotoxicity, we compared the behavior of 6294 to that of another invasive strain, PAO1, and determined whether the cytotoxicity could be related to quorum sensing. Both invasive strains, 6294 and PAO1, appear to have quorum-sensing systems that were operative when large doses of bacteria were applied to cultured lung epithelial cells or instilled into the lungs of animals. Nonetheless, only 6294 was cytotoxic. Cytotoxicity induced by 6294 correlated with increased elastase production. These experiments suggest that there are multiple mechanisms for the induction of cytotoxicity, pathology, and mortality in vivo. However, in vivo cytotoxicity and mortality, but not pathology, could be predicted by quantitative in vitro cellular damage experiments utilizing a range of bacteria-to-cell ratios. It appears that quorum sensing may inversely correlate with virulence in that strains that produced PAI [N-(3-oxododecanoyl) homoserine lactone] also appeared to attract more polymorphonuclear leukocytes in vivo and were possibly eliminated more quickly. In addition, exoproduct production in bacteriological medium in vitro may differ significantly from exoproduct expression from infections in vivo or during cocultivation of bacteria with tissue culture cells.
Insights
Pseudomonas aeruginosa strain 6294 caused cell damage through dose-dependent cytotoxicity linked to elastase, while quorum sensing may inversely correlate with virulence. In vitro models predicted in vivo outcomes for cytotoxicity and mortality.
Area of Science:
- Microbiology
- Bacterial Pathogenesis
- Cell Biology
Background:
- Pseudomonas aeruginosa exhibits invasive and cytotoxic phenotypes.
- The role of quorum sensing in P. aeruginosa cytotoxicity is not fully understood.
- High bacterial inoculums of invasive strains can induce cytotoxicity.
Purpose of the Study:
- To investigate the dose-related cytotoxicity of P. aeruginosa.
- To determine if cytotoxicity is linked to quorum sensing.
- To compare cytotoxic mechanisms between P. aeruginosa strains.
Main Methods:
- Comparing cytotoxic effects of P. aeruginosa strains 6294 and PAO1 on lung epithelial cells.
- Assessing quorum sensing activity in both strains.
- Measuring elastase production.
- Correlating in vitro cytotoxicity with in vivo outcomes (cytotoxicity, pathology, mortality) in animal models.
Main Results:
- Both invasive strains, 6294 and PAO1, utilized quorum sensing at high doses.
- Only strain 6294 demonstrated cytotoxicity, correlating with increased elastase production.
- In vitro cytotoxicity assays predicted in vivo cytotoxicity and mortality, but not pathology.
- Strains producing N-(3-oxododecanoyl) homoserine lactone (PAI) attracted more polymorphonuclear leukocytes and were cleared faster, suggesting an inverse correlation between quorum sensing and virulence.
Conclusions:
- Multiple mechanisms contribute to P. aeruginosa-induced cytotoxicity, pathology, and mortality.
- Quorum sensing may inversely correlate with virulence in P. aeruginosa.
- In vitro models can predict in vivo cytotoxicity and mortality.
- Exoproduct expression in vitro may differ from in vivo conditions.