Bacteriophage virus on a bacterium, computer artwork. Bacteriophages, or phages, are viruses that infect bacteria. A bacteriophage consists of an icosahedral (20-sided) head, which contains the genetic material (red), a 'tail' with fibres that fix the bacteriophage to a specific receptor site on the bacterium, as seen here. The 'tail' then injects the genetic material into the bacterium, and the cellular machinery of the bacterium is used to produce more copies of the virus. The thick stalk-like structures are the bacteria's flagella, some seen spiralling away into the background.