What is a Bacteriophage?
A bacteriophage is a virus that infects bacteria. These intracellular parasites first latch onto the bacteria and then inject their DNA. Then they reproduce in the cell cytoplasm by commandeering all or some of the host cell biosynthetic machinery. After approximately 100 new phages have been created they burst out of the cell, killing it in the process, and move onto their next bacterial targets.
The word bacteriophage comes from the Greek "phagein" which means eater of bacteria. However, phages don’t actually eat bacteria.
Bacteriophage therapy is not a new idea. Phages were discovered twice in the early 20th century – by Frederick Twort and Felix d’Hérelle in 1915 and 1917. Because of phage penchant for bacteria, it did look like they would be useful in the fight against disease. But when antibiotics came onto the scene in the 1940s the West lost interest in them. However, studies continued elsewhere, particularly in the Soviet Union where it was used to treat soldiers fighting in World War II. Today, page therapy is still in widespread use in Georgia.
In the West the field is undergoing something of a mini renaissance, largely fuelled by the rise in antibiotic resistant bacteria. Scientists are looking closely at bacteriophage parts and functions to see how they might develop new treatments against drug resistant microbes.
Bacteriophage Parts and Function
One of those scientists studying bacteriophage parts and functions is Sun Qingan from Texas A & M University. He’s been looking at how phages get out of bacterial cells once they have replicated. There are a number of obstacles that are in their way – namely, a cell membrane and a cell wall. But Qingan found out how they are able to destroy the cell wall from the inside
The weapon of choice is an enzyme called endolysin. When it is first synthesized it attaches to the membrane and is inactive. But on leaving the membrane it suddenly restructures and gains the power to send the cell wall packing. Qingan draws analogy with Transformers, the science fiction robots that can turn into vehicles or other objects.
The key to the biological transformation is a region of the enzyme called the SAR domain which controls the restructuring process and tells the enzyme when to transform.
Qingan hopes that knowing more about the transformation will provides researchers with a possible way of being able to destroy bacterial cells to stop an infection from proceeding. This could be useful for the development of phage therapy.
Advantages and Disadvantages of Phage Therapy
- Phages are very specific, so they will not harm beneficial bacteria in the body
- Once the bacteria is destroyed phage action ceases as they no longer have a host – and so will disperse harmlessly
- Phage therapy could be useful for people who are allergic to antibiotics
- There is a huge diversity of phages – a potential problem if the bacteria to be treated is unknown
- Some phages are quickly excreted from the bloodstream, having been recognised by the immune system.