Related Experiment Videos
Infectivity of Legionella pneumophila mip mutant for alveolar epithelial cells
N P Cianciotto1, J K Stamos, D W Kamp
1Department of Microbiology-Immunology, Northwestern University, Chicago, IL 60611.
Abstract:
Legionella pneumophila can invade and grow within explanted alveolar epithelial cells. Given its potential clinical significance, an examination of the molecular basis of epithelial cell infection was initiated. The mip gene encodes a 24-kilodalton surface protein that promotes macrophage infection and virulence. To determine whether this gene is required for pneumocyte infection, we tested a strain bearing a mip null mutation for its ability to infect both explanted type II cells and type I-like cell lines. For infection of type II cells, the infective dose 50% for the Mip-strain was 25-fold higher than an isogenic Mip+ strain. Type I cell monolayers infected with the mutant for 3 days yielded approximately 50-fold fewer bacteria than did monolayers infected with the parental strain. These data indicate that Mip enhances infection of pneumocytes and that L. pneumophila employs some of the same genes (mechanisms) to infect epithelial cells and macrophages.
Insights
Legionella pneumophila uses the Mip protein to infect lung epithelial cells. This finding reveals shared mechanisms between epithelial and macrophage infections by this bacterium.
Area of Science:
- Microbiology
- Cell Biology
- Infectious Diseases
Background:
- Legionella pneumophila is an intracellular bacterium capable of infecting alveolar epithelial cells.
- The Mip gene encodes a surface protein crucial for virulence in macrophage infections.
Purpose of the Study:
- To investigate the role of the Mip gene in Legionella pneumophila infection of lung epithelial cells (pneumocytes).
- To determine if Mip is essential for L. pneumophila to invade and replicate within epithelial cells.
Main Methods:
- Utilized a mip null mutant strain of L. pneumophila.
- Assessed bacterial infectivity in explanted type II alveolar epithelial cells and type I-like cell lines.
- Compared the infective dose 50% (ID50) and bacterial counts between Mip-deficient and wild-type strains.
Main Results:
- The Mip-deficient strain showed a 25-fold higher ID50 for type II cell infection compared to the Mip+ strain.
- Type I cell monolayers infected with the Mip mutant yielded approximately 50-fold fewer bacteria after 3 days.
- These results demonstrate that Mip significantly enhances L. pneumophila infection of pneumocytes.
Conclusions:
- The Mip protein plays a critical role in L. pneumophila's ability to infect lung epithelial cells.
- L. pneumophila utilizes conserved virulence mechanisms, including the Mip protein, to infect both epithelial cells and macrophages.