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Identification and characterization of hemolysin-like proteins similar to RTX toxin in Pasteurella pneumotropica

Hiraku Sasaki1, Eiichi Kawamoto, Yoshikazu Tanaka

  • 1Animal Research Center, Tokyo Medical University, 6-1-1, Shinjuku, Tokyo, Japan. h-sasaki@tokyo-med.ac.jp

Journal of Bacteriology
|April 14, 2009
PubMed

Insights

Researchers identified two RTX toxins, PnxIA and PnxIIA, in the rodent pathogen Pasteurella pneumotropica. These toxins showed hemolytic activity and were present in a majority of isolates, suggesting they are virulence factors.

Area of Science:

  • Microbiology
  • Bacterial Pathogenesis
  • Molecular Biology

Background:

  • Pasteurella pneumotropica is an opportunistic pathogen causing severe pneumonia in immunodeficient rodents.
  • The specific virulence factors contributing to P. pneumotropica pathogenicity are largely unknown.

Purpose of the Study:

  • To identify and characterize RTX toxins in P. pneumotropica.
  • To investigate the genetic organization and expression of these toxins.
  • To assess the prevalence and hemolytic activity of these potential virulence factors.

Main Methods:

  • Gene identification and sequencing of RTX toxins (pnxIA, pnxIIA) from P. pneumotropica ATCC 35149.
  • Analysis of gene organization, including operon structures and RTX repeat sequences.
  • Quantitative PCR to determine gene expression levels during bacterial growth phases.
  • Recombinant protein expression in Escherichia coli to assess hemolytic activity.
  • Southern blotting to evaluate the prevalence of toxin genes in clinical isolates.

Main Results:

  • Two RTX toxin genes, pnxIA and pnxIIA, were identified. PnxIA is part of an operon including secretion system genes, while pnxIIA encodes only the toxin.
  • Both PnxIA and PnxIIA contain RTX repeat sequences, indicative of their toxin nature.
  • pnxIA gene expression increased from early to late log phase, while pnxIIA expression rose from late log to early stationary phase.
  • Recombinant PnxIA and PnxIIA exhibited weak hemolytic activity against sheep and murine erythrocytes.
  • The pnxIA gene was detected in 82% of isolates, and pnxIIA in 39%.

Conclusions:

  • The identified RTX toxins, PnxIA and PnxIIA, are likely virulence factors in Pasteurella pneumotropica.
  • The differential expression and prevalence of these toxins suggest their roles in the pathogenesis of rodent pneumonia.
  • Further studies are warranted to elucidate the precise mechanisms of these RTX toxins in P. pneumotropica infections.

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