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What are Bacteriophages?

by 5m Editor
13 June 2005, at 12:00am

By Frank T. Jones, Lisa Bielke and Jack Higgins, Center of Excellence for Poultry Science at the University of Arkansas's Avian Advice - Don’t let the big word (bacteriophage) scare you. Bacteriophages (sometimes called phages) are viruses that infect bacteria. The word “phage” means to eat, so the literal meaning of the word bacteriophage is “bacteria eater”. It may seem strange that creatures as small as bacteria could be infected with a virus, but bacteriophages are about 40 times smaller than bacteria and have apparently been around about as long as bacteria have. This article will provide an outline of how bacteriophages function and their possible benefits.

What are Bacteriophages? - By Frank T. Jones, Lisa Bielke and Jack Higgins, Center of Excellence for Poultry Science at the University of Arkansas's Avian Advice - Don’t let the big word (bacteriophage) scare you. Bacteriophages (sometimes called phages) are viruses that infect bacteria. The word “phage” means to eat, so the literal meaning of the word bacteriophage is “bacteria eater”. It may seem strange that creatures as small as bacteria could be infected with a virus, but bacteriophages are about 40 times smaller than bacteria and have apparently been around about as long as bacteria have. This article will provide an outline of how bacteriophages function and their possible benefits.
The Author

Dr. Frank Jones
Extension Section Leader

Bacteriophage – Structure and Function

Bacteriophages have been compared to “space ships that are able to carry genetic material between susceptible cells and then reproduce in those cells” (Kutter, 1997). Bacteriophages are, in fact, very simple organisms that consist of genetic material (DNA or RNA) surrounded by a protein coat, a hollow protein tail and tail fibers. The general structure of a bacteriophage is shown in Fig. 1.

Figure 2 outlines the bacteriophage life cycle. Bacteriophages cannot reproduce without a bacterial cell. The bacteriophage particle attaches to a bacteria and binds to the cell. The particle then injects genetic material into the cell. The genetic material seizes control of the cell causing it to make additional bacteriophage genetic material.

In addition, the bacteriophage genetic material forces the cell to make protein coats, hollow protein tails and tail fibers, which are then assembled into new bacteriophage particles. Finally, when no more bacteriophage particles can be made, the cell breaks open, releasing the new bacteriophage particles into the environment to repeat the process with other bacterial cells. This process of infection, replication and release of new bacteriophage particles continues until there are no more cells to infect. However, the description of the bacteriophage life cycle may prompt questions. If this process happens with bacterial cells, what’s to keep it from happening with plant, animal or human cells?

The surface of each cell contains a unique blend of proteins, carbohydrates, fats and other organic compounds. The organic compounds on the surface of bacterial cells allow bacteriophages to recognize and attach only certain bacterial cells. If bacteriophages do not recognize the characteristic blend of proteins, carbohydrates and fats, they will not attach to the cell. This means that bacteriophages will not attach to cells unless they are bacteria. The organic compounds on the surface of plant, animal and human cells are not recognized by bacteriophages and they do not attach. In addition, the genetic material injected into cells by a bacteriophage is only capable of acting on bacterial internal contents. Since the internal contents (that is, the structure and chemistry) of plant, animal and human cells is different from that of bacterial cells, bacteriophage genetic material cannot seize control of the cell. This means that even if a bacteriophage attached and injected genetic material into a plant, animal or human cell, the material could not take over the internal machinery of those cells (Kutter, 1997). Because of the specificity of bacteriophages, they are considered safe and, indeed, bacteriophages have not been reported to infect plant, animal or human cells.

In fact, bacteriophages tend to be very specific in the bacteria they infect. For instance, a bacteriophage that infected an E. coli, would not infect a Salmonella. This specificity can be an advantage and a disadvantage. Specificity could mean that specific pathogenic organisms are knocked out, while beneficial organisms are left unharmed. However, when several organisms are responsible for a problem or infection within an animal, bacteriophages would have to be directed at each organism. Bacteriophages may be beneficial in treating human, animal and even plant diseases. In fact, it may surprise you to learn that bacteriophages (or phages) have been used to treat bacterial diseases for over 80 years in Eastern Europe (Anonymous1, ND). Indeed, in the 1970s and 80s the Soviet Union produced thousands of gallons of phage each month and every Soviet soldier carried a powder containing bacteriophage in his emergency medical pack (Anonymous1, ND). A brief examination of the history of bacteriophages may be helpful here.

A Very Brief History of Bacteriophage

In 1896 a researcher reported that when the waters of the Ganges and Jumna Rivers in India were filtered to remove the bacteria something in the waters was antibacterial. About 20 years later other researchers demonstrated that a virus was involved and named the virus “bacteriophage” (Anonmymous3, ND). In view of the fact that at the time sulfa drugs and antibiotics were not yet discovered, bacteriophages were explored as disease treatments. The first reported use of bacteriophage to treat a bacterial disease came from France in 1921 (Anonymous2, ND). Bacteriophages were used to treat a variety of diseases. They were taken orally, put on wounds, applied as aerosols, given as injections and used in eye drops. Success rates for bacteriophage therapy were reported to be 75 to 100%, depending on the pathogen involved (Anonmyous3, ND, Kutter, 1997). Indeed, bacteriophage products were produced by United States pharmaceutical companies and licensed for sale in the 1930s (Anonymous3, ND).

However, in the 1940s, new “miracle” drugs (antibiotics) became widely available and bacteriophage (or phage therapy) was largely abandoned by the western world (Kutter, 1997). However, current difficulties with antibiotic resistant bacteria have prompted researchers to re-examine bacteriophage.

Summary

Bacteriophages are viruses that infect only bacterial cells. Because of the specificity of bacteriophages, they are considered safe and have not been reported to infect plant, animal or human cells. Bacteriophages (or phages) have been used to treat bacterial diseases for over 80 years in Eastern Europe. Current difficulties with antibiotic resistant bacteria have prompted researchers to re-examine bacteriophage.

Literature Cited

Anonmyous1. no date. Bacteriophage or phage: A practical alternative to antibiotics.
http://isculpture.com/bacteriophage_or_phage.html visited April, 2005.

Anonymous2. no date. General information about bacteriophages.
http://www.phages.org/PhageInfo.html visited April, 2005.

Anonymous3. no date. Phage history. http://www.intralytix.com/history.html visited April, 2005.

Kutter, E. 1997. Phage therapy. http://www.evergreen.edu/phagetherapy/phagetherapy.html visited April, 2005.

Source: Avian Advice - Spring 2005 - Volume 7, Number 2