Mitis group streptococci express variable pilus islet 2 pili.
Dorothea Zähner1, Ashish R Gandhi, Hong Yi
1Division of Infectious Diseases, Department of Medicine, Atlanta, Georgia, United States of America. dzahner@emory.edu
Plos One
|October 4, 2011
Summary
Pilus-islet 2 (PI-2) pili were identified in oral streptococci, revealing significant genetic diversity due to horizontal gene transfer. This pilus variation may explain differences in bacterial interactions and disease potential within this group.
Area of Science:
- Microbiology
- Genetics
- Molecular Biology
Background:
- Mitis group streptococci, including Streptococcus oralis, Streptococcus mitis, and Streptococcus sanguinis, are key players in oral biofilm formation, dental plaque, and infective endocarditis.
- These bacteria engage in complex bacteria-bacteria and bacteria-host interactions.
- The human pathogen Streptococcus pneumoniae utilizes pilus-islet 2 (PI-2) encoded pili for adhesion to host cells.
Purpose of the Study:
- To investigate the presence and characteristics of PI-2 pili in Mitis group oral streptococci.
- To explore the genetic diversity and evolutionary mechanisms, such as horizontal gene transfer, of PI-2 pili in these species.
- To understand the potential role of PI-2 pili in the pathogenic traits of Mitis group streptococci.
Main Methods:
- Identification and genetic analysis of PI-2 pilus-encoding islets in oral streptococci isolates.
- Sequencing and comparative analysis of pitA and pitB genes, encoding structural pilus proteins.
- Development of polyclonal antisera against PitA and PitB for immunodetection of pili.
- Electron microscopy to visualize pilus structures.
- Electronic multilocus sequence analysis for phylogenetic assessment.
Main Results:
- PI-2 pilus-encoding genetic islets were found in specific isolates of S. oralis, S. mitis, and S. sanguinis, but not universally.
- The identified PI-2 islets showed variations in pitA and pitB genes compared to S. pneumoniae, with multiple variants identified.
- Evidence of intra- and interspecies horizontal gene transfer was indicated by species-independent combinations of pitA and pitB variants.
- Electron microscopy confirmed the presence of pili on the bacterial surface, with lengths exceeding 700 nm.
- Antiserum cross-reactivity suggested distinct interactions between pilus variants and antibodies.
Conclusions:
- This study represents the first identification of PI-2 pili in Mitis group oral streptococci.
- The findings highlight horizontal gene transfer as a significant driver of genetic diversity for PI-2 pili within these bacteria.
- The observed diversity in PI-2 pili offers a potential link to strain-specific interactions, tissue tropisms, and pathogenic capabilities in Mitis group streptococci.
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