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Infectious Diseases

30 January 2008

Viruses vs. bacteria

Bacteriophage (or 'phage' for short) therapy, is an alternative to antibiotic treatment, and has recently been gaining favour and appeal amongst western scientists.

Bacteriophage (or 'phage' for short) therapy, is an alternative to antibiotic treatment, and has recently been gaining favour and appeal amongst western scientists.

This treatment involves injecting or applying a cocktail of bacteriophages, which consist of a virus that attacks specific infection-causing bacteria. In short, the bacteriaphages "eat" the bacterium concerned.

Phage therapy is currently the subject of mainstream research and application in Georgia in the former Soviet Union.

History
The history of phage therapy can be traced as far back as 1896. M.E Hankin reportedly witnessed the antibacterial action of the Indian rivers Ganga and Yamuna against the bacterial strain Vibrio Chlorae. Hankin’s findings are said to have explained the low numbers of cholera cases among people who consumed the river water.

In 1915 and 1917, Frederick Twort and Felix d'Hérelle from England reported similar results. It was d'Hérelle who named these ultra-microbes ‘bacteriophages’ (bacteria eaters) and who pioneered the use of phages for treating Shigella dysentery in France. Around the same time, a Georgian by the name of George Eliava was conducting phage research of his own.

Eliava met d'Hérelle at the Pasteur Institute in Paris, after which he established the Eliava Institute in Tbilisi, Georgia, dedicated to the further study of phages.

How they work
Bacteriophages are divided into two types: lytic and lysogenic. References to bacteriophages for therapeutic reasons allude to lytic bacteriophages. Lysogenic phages are not useful for therapeutic purposes.

Phages attach themselves onto bacteria and inject their DNA into the cells. In a matter of minutes, a bacterium becomes a phage factory, producing more and more phages after having corrupted the reproductive mechanism of the bacterium. Eventually the new phages burst through the walls of the cell, destroying the bacterium and continuing the process by spreading to other bacterial cells.

By nature, most phages are ‘bacterium-specific’, meaning that they can only affect specific strains within a species. Phage therapy therefore results in less harm to the body than traditional antibiotic treatment. This also helps prevent secondary infections usually caused by the use of antibiotics.

The manner in which phages are applied depends on the type of condition from which a patient suffers. They can be applied topically, during surgery or orally. They can also be applied by means of injection. The nature of the immune system (that automatically fights against any viruses introduced into the bloodstream or lymphatic system) means that injected bacteriophages are only used on rare occasions, such as when no other method of application would be effective.

Better than antibiotics?
Bacteria eventually grow resistant to antibiotics, but phages are able to change and adapt in ways that make them a constant threat to bacteria. All viruses change and adapt themselves in time, and bacteriophages are no exception. Also, phages have the advantage of being able to penetrate deeper into an infected area than antibiotics can, because phages keep reproducing, unlike antibiotics, which eventually lose efficacy.

On a practical level, phages are more viable than antibiotics for a number of reasons. These include:

  • There are almost no serious side-effects (antibiotic use can result in secondary infections).

  • Selecting new phages to combat an infection is a much quicker process than finding new antibiotics, which sometimes take up to several years.
  • Phages replicate at the site of infection, but antibiotics are eliminated from the body after they’re metabolised.

Sources:
Biotech Journal (www.biotechjournal.com), Phage Therapy Centre (www.phagetherapycentre.com), Wikipedia (www.wikipedia.org)

André van Wyk, Health24

 

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