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The virtue of training: extending phage host spectra against vancomycin-resistant Enterococcus faecium strains using
Julien Lossouarn1, Elsa Beurrier1, Astrid Bouteau1
1Université Paris-Saclay, INRAE, AgroParisTech, Micalis Institute, Jouy-en-Josas, France.
Abstract:
Phage therapy has (re)emerged as a serious possibility for combating multidrug-resistant bacterial infections, including those caused by vancomycin-resistant Enterococcus faecium strains. These opportunistic pathogens belong to a specific clonal complex 17, against which relatively few phages have been screened. We isolated a collection of 21 virulent phages growing on these vancomycin-resistant isolates. Each of these phages harbored a typical narrow plaquing host range, lysing at most 5 strains and covering together 10 strains of our panel of 14 clinical isolates. To enlarge the host spectrum of our phages, the Appelmans protocol was used. We mixed four out of our most complementary phages in a cocktail that we iteratively grew on eight naive strains from our panel, of which six were initially refractory to at least three of the combined phages. Fifteen successive passages permitted to significantly improve the lytic activity of the cocktail, from which phages with extended host ranges within the E. faecium species could be isolated. A single evolved phage able to kill up to 10 of the 14 initial E. faecium strains was obtained, and it barely infected nearby species. All evolved phages had acquired point mutations or a recombination event in the tail fiber genetic region, suggesting these genes might have driven phage evolution by contributing to their extended host spectra.
Insights
Phage therapy offers a promising solution for multidrug-resistant infections. Evolving phages through specific protocols can broaden their host range against challenging bacteria like vancomycin-resistant Enterococcus faecium.
Area of Science:
- Microbiology
- Bacteriology
- Virology
Background:
- Multidrug-resistant bacterial infections, particularly vancomycin-resistant Enterococcus faecium (VRE), pose a significant global health threat.
- Phage therapy is re-emerging as a viable alternative to antibiotics for combating these resistant strains.
- Limited phage effectiveness against specific VRE clonal complexes necessitates strategies to broaden phage host ranges.
Purpose of the Study:
- To isolate and characterize virulent phages effective against vancomycin-resistant Enterococcus faecium.
- To enhance the host spectrum of isolated phages through an iterative protocol.
- To investigate the genetic basis for the extended host range of evolved phages.
Main Methods:
- Isolation of 21 virulent phages targeting vancomycin-resistant Enterococcus faecium.
- Application of the Appelmans protocol involving iterative phage cocktail passages on resistant strains.
- Genetic analysis of evolved phages to identify mutations or recombination events.
Main Results:
- Initial phages exhibited narrow host ranges, lysing a maximum of 5 strains each.
- Iterative passages significantly improved the lytic activity and host range of the phage cocktail.
- Evolved phages demonstrated an extended host range, with one phage lysing up to 10 of 14 clinical isolates.
- Genetic analysis revealed mutations or recombination in the tail fiber region of evolved phages.
Conclusions:
- Phage therapy can be enhanced to target specific multidrug-resistant pathogens.
- Iterative evolution protocols, like the Appelmans protocol, are effective in broadening phage host ranges.
- Tail fiber genes play a crucial role in the evolution of phage host specificity.
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