How is phage cocktail prepared?

One of the major advantages of bacteriophages as antimicrobials is their specificity. A consequence of this characteristic is that they are not only innocuous to eukaryotic cells, but also to all prokaryotic cells outside their host range. This would ensure that the normal microbiota remains intact during therapy/application, which in turn would be expected to help prevent secondary infections and probably accelerate recovery. Indeed, there is growing proof that the microorganisms inhabiting our bodies play very important roles in our overall health. Antibiotic treatment, by contrast, can severely affect our normal microbiota due to their more general, broad-range action, which often results in serious side effects. But being specific brings in a problem to phage preparations too, most single preparation won't be able to clear a wide range of pathogens especially phage resistant strains. Phage cocktail is applied to widen the host range.
Phage cocktail art by Dr. Ellie Jameson Twitter account

What is a phage cocktail?

A phage cocktail can be simply referred to as a mixture of two or more purified phages of different traits of interest for the purpose of exploiting their combined potential during application. Phage cocktails are intended to broaden the utility for phage formulations to treat specific bacterial diseases and to prevent the development of phage-resistant bacterial mutants. Phage cocktails tend to be more efficient compared to single phage preparations.  Monophage therapy involves the application of only a single phage type, whereas polyphage therapy is the application of a phage cocktail.

How is a phage cocktail made?

The phage cocktail is made using a simple mixing strategy, most people make it by pooling equal volumes of each purified phage preparation at a certain concentration of their choice mostly basing on the application. Phage scientists prefer using the step-by-step (SBS) preparation strategy. Phage cocktail is more effective in reducing bacterial mutation frequency than monophage suggesting that phage cocktail established by SBS method has great therapeutic potential for multidrug-resistant bacteria infection.
Steps involved in the development of phage therapy strategies. In the phage characterization step, text in green and red respectively correspond to desirable and undesirable characteristics in a phage for therapeutic applications. Abbreviations: SBS method, step-by-step method. by Fern├índez et al (2019).

Things to consider when making a phage cocktail

  1. All candidate phages must be purified.
  2. All candidate phages must have been tested and characterized independently.
  3. Screening for undesirable genes is advised especially if the cocktail is for medical use.
  4. The concentration of phage candidates must be known
  5. Specific but not too specific
  6. All candidates must be virulent

Advantages of using phage cocktail

  1. Wide host range compared to individual candidates.
  2. Help in clearing phage-resistant mutant bacteria.
  3. Produce hybrid of good traits of individual phage candidates.
  4. Increase efficiency and reduce the time taken for a bacteria to be killed.
  5. Increase antibiofilm potential
  6. Increase the preparation stability

Bacteriophage could be an alternative to antibiotics for the treatment of multidrug-resistant bacterial infections. Indeed, it has proven to be medically superior to antibiotic therapy in many ways. However, the emergence of phage-resistant variants was observed rapidly if only one phage strain was used against a particular bacterium. Fortunately, there is an abundance of other phage species which possess lytic ability against resistance-obtained variants. Therefore phage cocktails can help in lysing the mutants.

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