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Role of exotoxin A in inducing severe Pseudomonas aeruginosa infections in mice
S Miyazaki1, T Matsumoto, K Tateda
1Department of Microbiology, Toho University School of Medicine, Tokyo, Japan.
Abstract:
The effects of exotoxin A (EXA) from Pseudomonas aeruginosa on polymorphonuclear leucocytes (PMNLs) were studied in a mouse model and in vitro. P. aeruginosa PA103, which produced EXA, was 20 times more virulent for normal mice than was its EXA-deficient mutant, PA103-29. EXA was detected in the plasma of mice infected with P. aeruginosa PA103, and its presence correlated with increasing numbers of bacteria in the blood and internal organs. A monoclonal antibody (MAb) against EXA prevented the death of the mice if it was given simultaneously with, or 2 h before, infection with strain PA103. The number of PMNLs in murine blood decreased by 50% within 30 min of intravenous injection of EXA, but this decrease was prevented by simultaneous or prior injection of MAb to the toxin. EXA inhibited in-vitro phagocytosis and killing of P. aeruginosa by human and murine PMNLs and decreased the number of the PMNLs by between 60 and 68%. Collectively, these results not only confirm that EXA is toxic in vivo, but also suggest that this toxin accelerates the growth of virulent P. aeruginosa in mice.
Insights
Pseudomonas aeruginosa exotoxin A (EXA) significantly increases virulence in mice and impairs polymorphonuclear leucocytes (PMNLs). Neutralizing EXA protects against infection, indicating its critical role in disease progression.
Area of Science:
- Microbiology
- Immunology
- Toxicology
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen.
- Exotoxin A (EXA) is a key virulence factor produced by P. aeruginosa.
- Polymorphonuclear leucocytes (PMNLs) are crucial immune cells involved in combating bacterial infections.
Purpose of the Study:
- To investigate the in vivo and in vitro effects of Pseudomonas aeruginosa exotoxin A (EXA) on polymorphonuclear leucocytes (PMNLs).
- To determine the role of EXA in the virulence of P. aeruginosa infections in a mouse model.
Main Methods:
- Infection of mice with virulent P. aeruginosa and its EXA-deficient mutant.
- Detection of EXA in plasma and correlation with bacterial load.
- Administration of a monoclonal antibody (MAb) against EXA to assess protective effects.
- In vitro assays to evaluate the impact of EXA on PMNL function (phagocytosis, killing) and viability.
Main Results:
- P. aeruginosa producing EXA was 20 times more virulent than its EXA-deficient mutant.
- EXA presence in plasma correlated with bacterial dissemination.
- MAb against EXA conferred protection against lethal infection.
- EXA significantly reduced PMNL counts in vivo and inhibited PMNL phagocytosis and killing of P. aeruginosa in vitro.
Conclusions:
- Exotoxin A is a major virulence factor for Pseudomonas aeruginosa in vivo.
- EXA directly impairs the function and viability of polymorphonuclear leucocytes.
- Targeting EXA with neutralizing antibodies is a potential therapeutic strategy against P. aeruginosa infections.