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In vitro bioassay of endotoxin using fluorescein as a pH indicator in a macrophage cell culture system

Dong Hee Lee1, Hak-Joon Sung, Dong-Wook Han

  • 1Department of Medical Engineering, Yonsei University College of Medicine, 134 Shinchon-dong, Seodaemun-gu, Seoul 120-752, Korea.

Yonsei Medical Journal
|April 30, 2005
PubMed

Insights

A novel endotoxin detection method utilizes macrophage culture media and fluorescein, showing dose-dependent reductions in spectra. This system effectively detects lipopolysaccharide (LPS) and bacteria, complementing the Limulus Amebocyte Lysate (LAL) test.

Area of Science:

  • Biotechnology
  • Microbiology
  • Cell Biology

Background:

  • Endotoxins, primarily lipopolysaccharide (LPS) from Gram-negative bacteria, are potent pyrogens.
  • Current detection methods like the Limulus Amebocyte Lysate (LAL) test have limitations in detecting certain bacterial types or endotoxin concentrations.

Purpose of the Study:

  • To develop and evaluate a new endotoxin detection method using macrophage culture media and a pH-indication system.
  • To compare the efficacy of the novel method with the established LAL test for detecting various bacterial endotoxins and lysed bacteria.

Main Methods:

  • RAW 264.7 macrophage cells were cultured and treated with purified bacterial lipopolysaccharide (LPS) from Salmonella minnessota, Escherichia coli, and Pseudomonas aeruginosa.
  • Fluorescein was added to the LPS-treated macrophage culture media, and its absorption and emission spectra were measured.
  • The novel method's performance was compared to the LAL test, including its ability to detect lysed Gram-positive bacteria (Staphylococcus aureus).

Main Results:

  • Lipopolysaccharide (LPS) treatment of RAW 264.7 cells led to a reproducible, dose-dependent reduction in fluorescein's absorption and emission spectra.
  • The novel macrophage culture system detected reduced fluorescein intensity with lysed Staphylococcus aureus, which is often undetectable by the LAL test.
  • The new method demonstrated a dose-response relationship for both Gram-negative bacterial LPS and Gram-positive lysed bacteria.

Conclusions:

  • A novel endotoxin detection method based on a macrophage culture system and pH-indication using fluorescein has been developed.
  • This method shows promise as a sensitive and versatile tool for detecting lipopolysaccharide (LPS) from Gram-negative bacteria and lysed Gram-positive bacteria.
  • The proposed system could serve as a valuable supplement to the existing Limulus Amebocyte Lysate (LAL) assay for broader bacterial detection.

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