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Bacteria can be ill


Elsewhere in this museum it is described how infectious diseases can be caused by viruses. These minute creatures live parasitic in other cells. Some have viruses have adapted to live in bacterial cells. They are called bacteriophages.

Bacteriophages, viruses that live in bacteria, can have different shapes, and some even resemble little space-shuttles.

Bacteriophages are able to attach themselves to (certain types of) bacteria and to inject their genetic material in the bacterial cell. After this happens, their existence becomes more difficult to describe, for only their genetic material (in the form of DNA) exists in the bacterial cell. Then, using the bacterial machinery, the DNA multiplies itself. Eventually from this multiplied genetic information so many new bacteriophages are formed that the cell bursts. The offspring of the bacteriophage has destroyed its bacterial host, and in so doing millions of new bacteriophages are released. These can attach themselves to new bacteria to complete their life cycle.

How do we notice that bacteriophages are present in bacteria? We can see bacteria when they grow, eg. a liquid will become cloudy if there are enough bacteria present (check how our senses can detect bacteria). When we grow bacteria in the laboratory on agar plates, they can completely cover this plate with a confluent layer of growth. If  bacteriophages are present in this culture, they will produce holes in this confluent layer. The hole, called a 'plaque', is circular because phages cannot move, so when the originally infected bacterial cell bursts, the neighboring cells become infected only. This process produces a round-shaped spread of phages, thus a perfectly round 'plaque'. A liquid that is cloudy from bacteria will become clear again when bacteriophages destroy all cells present. However, bacteriophages do not always kill their host, at least not immediately. Like all infectious organisms, bacteriophages could never make their host extinct, for they are dependent on their host bacteria to survive. This is also true for infectious diseases: they cannot make their target host extinct. See our display on infectious bacterial diseases.

When bacteriophages kill bacteria, can they be used to cure us from pathogenic bacteria? Indeed, phage therapy has been used in the past to cure infectious diseases, especially in Eastern Europe and Russia, and research is continuing. Can phages provide a Nature-friendly way to fight bacteria? (Source: BI Koerner). BBC Radio provides a transcript of a program on phage therapy (Source: BBC).

Bacteriophages are important tools in bacteriological research. They can be used as vehicles to introduce DNA into a bacteria. Phages don't mind to take along foreign DNA when they insert their own DNA into a bacterial cells. Microbiologists can make use of this. However, they make sure to keep the phages under control otherwise all their precious bacterial cultures become infected! The formation of mutations in a bacterial population can be nicely demonstrated with bacteriophages.


The content of this page is copyright of the Virtual Museum of Bacteria and was written by Dr. T. M. Wassenaar (curator), with support of the Foundation for Bacteriology.

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Page last modified: 08 Mar 2007

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