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Streptococcus iniae phosphoglucomutase is a virulence factor and a target for vaccine development
John T Buchanan1, Jason A Stannard, Xavier Lauth
1Department of Pediatrics, University of California, San Diego, School of Medicine, La Jolla, 92093, USA. jtbuchan@ucsd.edu
Infection and Immunity
|September 24, 2005
Summary
Researchers identified a key gene (phosphoglucomutase or pgm) in Streptococcus iniae essential for virulence. Disrupting this gene created an attenuated mutant, showing potential as a live vaccine for fish aquaculture.
Area of Science:
- Microbiology
- Fish Immunology
- Bacteriology
Background:
- Streptococcus iniae causes significant health and economic losses in global fish populations.
- Identifying virulence factors is crucial for developing effective disease control strategies in aquaculture.
Purpose of the Study:
- To identify genetic factors contributing to Streptococcus iniae virulence.
- To evaluate the potential of attenuated S. iniae mutants as live vaccines.
Main Methods:
- Random Tn917 mutagenesis and high-throughput screening in hybrid striped bass (HSB) model.
- Genetic analysis of S. iniae mutants, including disruption of the phosphoglucomutase (pgm) gene.
- In vitro assays for antimicrobial peptide resistance and in vivo challenge studies in HSB.
Main Results:
- A phosphoglucomutase (pgm) gene mutant (DeltaPGM) exhibited reduced capsule thickness and cell wall rigidity.
- The DeltaPGM mutant was more susceptible to HSB blood clearance and cationic antimicrobial peptides.
- In vivo, the DeltaPGM mutant was severely attenuated, with 1000x lethal dose causing only 2.5% mortality.
- Reintroduction of the pgm gene restored virulence and antimicrobial peptide resistance.
Conclusions:
- The pgm gene is essential for S. iniae virulence, impacting cell wall structure, capsule expression, and resistance to innate immunity.
- The attenuated DeltaPGM mutant stimulated protective immunity in fish, indicating its potential as a live attenuated vaccine for aquaculture.