Bacteriophage evolution during phage therapy, the story of a ménage à trois
Bacterial pathogens infecting the human gastrointestinal tract must share their infectious site with a huge diversity of commensal bacteria. While the therapeutic potential of virulent bacteriophages in killing gut pathogens has already been demonstrated in experimental settings, nothing is known about their long-term evolution in such complex environment.
We setup a murine model of Escherichia coli gut colonisation where the commensal strain MG1655 and the Adherent-Invasive E. coli (AIEC) strain LF82 persist over several weeks. We then selected LDS_P1, a Felix01-like bacteriophage, unable to infect or adsorb to strain MG1655 but active against different AIEC strains including LF82. LDS_P1 was fed to co-colonised mice or added to liquid co-cultures of these strains, and populations were monitored during seven weeks.
Both settings led to continuous persistence of both bacteria as well as bacteriophage replication. Remarkably, LDS_P1 populations were isolated from mice faecal samples having acquired the ability to infect strain MG1655 while maintaining their infectivity towards strain LF82. However, in vitro-evolving LDS_P1 never adapted to infect strain MG1655.
Population genomics was analysed to compare experimental groups and understand adaptation mechanisms. Interestingly, all newly MG1655-adapted LDS_P1 populations shared a specific single nucleotide polymorphism (SNP) in one tail fiber gene. On the other hand, different evolved populations significantly broadened or decreased their host-range when tested against a collection of more than one hundred Enterobacteriacae and additional mutations were hypothesised as responsible for such drastic variations. Environmental factors and molecular mechanisms underlying such co-evolution are currently under investigation.
Our work shows that not only bacteriophage-bacteria co-evolution follows different dynamics in vivo compared to in vitro, but can also take routes leading to important phenotypic divergence. In light of that, more attention should be drawn towards the ecological impact of using therapeutic bacteriophages in the gastrointestinal tract or other complex microbial environments.
We setup a murine model of Escherichia coli gut colonisation where the commensal strain MG1655 and the Adherent-Invasive E. coli (AIEC) strain LF82 persist over several weeks. We then selected LDS_P1, a Felix01-like bacteriophage, unable to infect or adsorb to strain MG1655 but active against different AIEC strains including LF82. LDS_P1 was fed to co-colonised mice or added to liquid co-cultures of these strains, and populations were monitored during seven weeks.
Both settings led to continuous persistence of both bacteria as well as bacteriophage replication. Remarkably, LDS_P1 populations were isolated from mice faecal samples having acquired the ability to infect strain MG1655 while maintaining their infectivity towards strain LF82. However, in vitro-evolving LDS_P1 never adapted to infect strain MG1655.
Population genomics was analysed to compare experimental groups and understand adaptation mechanisms. Interestingly, all newly MG1655-adapted LDS_P1 populations shared a specific single nucleotide polymorphism (SNP) in one tail fiber gene. On the other hand, different evolved populations significantly broadened or decreased their host-range when tested against a collection of more than one hundred Enterobacteriacae and additional mutations were hypothesised as responsible for such drastic variations. Environmental factors and molecular mechanisms underlying such co-evolution are currently under investigation.
Our work shows that not only bacteriophage-bacteria co-evolution follows different dynamics in vivo compared to in vitro, but can also take routes leading to important phenotypic divergence. In light of that, more attention should be drawn towards the ecological impact of using therapeutic bacteriophages in the gastrointestinal tract or other complex microbial environments.
Reference:
Phage Therapy I-T10-Oft-01
Session:
Phage Therapy 1: updates on treating human bacterial pathogens
Presenters:
Luisa De Sordi
Session:
Phage Therapy 1: Updates on treating human microbial pathogens
Presentation type:
Offered talk - 15 min
Room:
Main Auditorium
Chair/s:
Catherine Rees
Date:
Thursday, 21 July 2016
Time:
08:45 - 09:00