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Distribution of mip-related sequences in 39 species (48 serogroups) of Legionellaceae
S Riffard1, F Vandenesch, M Reyrolle
1UPRES EA1655, Faculté de Médecine René Laennec, Lyon, France.
Abstract:
The macrophage infectivity potentiator gene (mip) from Legionella pneumophila is a major virulence factor of the species. Thus, mip-detection by amplification has been proposed to assess the presence of L. pneumophila in clinical and environmental samples. The distribution of mip-related sequences within the Legionellaceae was studied by DNA amplification using mip-specific primers followed by Southern blot hybridization with an internal probe. Thirty-nine species (48 serogroups) of Legionellaceae were screened in this attempt. Using this approach, sequences related to mip were observed in 89% of the tested species including the most recently described L. fairfieldensis, L. lansingensis and L. shakespearei. In several cases, cloning and sequencing of the amplified products confirmed the high levels of similarity between the sequence found in non-pneumophila species with that of the L. pneumophila mip gene. This confirms previous reports that mip related genes are widespread among Legionellaceae and therefore specific detection of the species L. pneumophila cannot be based on mip-targeted amplification.
Insights
The macrophage infectivity potentiator gene (mip) is widespread in Legionellaceae, not exclusive to Legionella pneumophila. Therefore, mip-targeted amplification is unreliable for specifically detecting L. pneumophila in samples.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- The macrophage infectivity potentiator (mip) gene is a key virulence factor in Legionella pneumophila.
- Detection of mip is used to identify L. pneumophila in clinical and environmental samples.
Purpose of the Study:
- To investigate the distribution of mip-related sequences within the Legionellaceae family.
- To determine if mip-targeted amplification is a specific method for detecting L. pneumophila.
Main Methods:
- DNA amplification using mip-specific primers.
- Southern blot hybridization with an internal probe.
- Screening of 39 Legionellaceae species (48 serogroups).
- Cloning and sequencing of amplified products.
Main Results:
- Mip-related sequences were found in 89% of tested Legionellaceae species.
- High similarity was confirmed between mip sequences from non-pneumophila species and L. pneumophila.
- Recently described species like L. fairfieldensis, L. lansingensis, and L. shakespearei also contained mip-related sequences.
Conclusions:
- Mip-related genes are broadly distributed across the Legionellaceae family.
- Mip-targeted amplification is not a specific method for identifying Legionella pneumophila.
- Rethinking diagnostic strategies for L. pneumophila detection is necessary.