CH391L/S13/Phage Therapy

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Introduction to Phage Therapy




Year Discoverer, country, microbe sensitive to phage
1896 Hankin, British, Vibrio cholerae
1898 Gamaleya, Russian, Bacillus subtilis
1915 Twort, British, Staphylococcus
1917 d'Herelle, French-Canadian, Shigella



The first well-controlled phage therapy study in the West was in 2009, where the treatment group received bacteriophage targeting antibiotic resistant P. aeruginosa in chronic ear infections[2]. Bacterial counts were significantly reduced, with several patients cured.

Previous and Current Research Directions


Regular use of phage therapy occurs primarily in the Republic of Georgia, due to the presence of the Eliava Institute, which has researched phage therapy since the 1920s. However, synthetic biology has enabled entirely new approaches to phage therapy, such as engineering new abilities into the phage. One such ability is the degradation of the extracellular polysaccharides (EPS) produced by bacteria during infections[3]. Production of the EPS results in a biofilm, which protects the bacteria within from external harm, such as antibiotics and bacteriophages, limiting the damage to the cells on the surface. To break through this barrier, researchers modified T7 with the gene for dispersin B, an enzyme that degrades one of the key components of EPS. After bacteria on the surface of the biofilm are infected, they produce DspB along with new phage. After the cells lyse, the DspB can degrade the EPS, which exposes more bacteria to infection.

One concern of phage therapy is the rapid lysing of pathogenic cells which may contain endotoxins. Sudden, massive releases of toxin can cause dangerous amounts of inflammation. Therefore, phage that kill the targeted pathogen without disrupted the cell's integrity are of interest. This can be accomplished by that by modifying phage to express endonucleases and holins, which are toxic to the cell (chopping DNA and making non-catastrophic disruptions to the cellular membrane)[4]. Toxin release was minimized, which decreased inflammation and increased the survival rate of treated mice.

Featured Paper

Enhancing antibiotic killing via modified phage. The M13 phage carries a copy of lexA3, which controls the activation of the SOS DNA damage repair response. Production of LexA3 prevents the cell from responding to the action of the antibiotic ofloxacin.

Phage therapy can be combined with conventional antibiotic treatment as a lethality enhancer. This is especially useful when trying to avoid quickly evolving resistance to the phage being used. In this approach, the antibiotics provide the killing blow, while the phage assist by suppressing gene networks that are not directly impacted by the antibiotics. One example of this was the combination of ofloxacin (which damages DNA by inhibiting the ligation action of DNA gyrase, while preserving the DNA cutting ability) with phage suppressing the SOS response, which repairs damaged DNA[5]. M13 phage (a non-lytic, filamentous phage) were engineered to overproduce LexA when infecting E. coli, which prevents the SOS response from occurring. When combined with ofloxacin, lexA phage increased killing by 2.7 orders of magnitude compared with using the non-LexA phage, and increased killing by 4.5 orders of magnitude compared to using ofloxacin alone.

The modified M13 phage was designed to be used in conjunction with quinolones, since they result in DNA damage. However, the lexA phage was also found to enhance other antibiotics, such as gentamicin (a aminoglycoside, which inhibit protein synthesis) and ampicillin (a beta-lactam, which interferes with cell-wall formation). The lexA phage could also restore the action of antibiotics against mutated, resistant bacteria, and against persisters (survivors from a previous round of antibiotic treatment).

The same study also targeted other non-essential genes to influence other systems within the cell (oxidative stress response and carbon storage regulation) to demonstrate the flexibility of this system. Similar to the earlier approach, genes controlling these pathways were over-expressed, preventing the cells from appropriately responding to the damage done to them.



Future Directions

Phage therapy can be used to rapidly (as compared to small-molecule research) develop anti-bacterial treatments, to both supplement and complement antibiotic usage. As the featured paper shows, synthetic biology can add novel features to phage, going far beyond what could be discovered in nature. In the future, there may be customized phage preparations for pathogens, and the adaptability and flexibility of phages ensures that new treatments can be developed as the pathogens evolve. In this way, phage are the ultimate weapon in the arms race between medicine and bacterial infections.

Phages also present an opportunity for preventive medicine, either in the form of modified phage preparations (which could be continually tweaked and updated, depending on current infection trends), or through the use of probiotics as described in the iGEM section. Future doctor visits could include a checkup on our microbiome, where the current members of the community are isolated, modified with friendly phage, and reintroduced to help ward off infections.



    Recent minireview of phage research.

  2. Wright A, Hawkins CH, Anggård EE, and Harper DR. A controlled clinical trial of a therapeutic bacteriophage preparation in chronic otitis due to antibiotic-resistant Pseudomonas aeruginosa; a preliminary report of efficacy. Clin Otolaryngol. 2009 Aug;34(4):349-57. DOI:10.1111/j.1749-4486.2009.01973.x | PubMed ID:19673983 | HubMed [ear]

    First well-controlled phase I/II study of bacteriophages in the West, to treat chronic ear infections.







All Medline abstracts: PubMed | HubMed