Bacteriophage viruses, computer artwork. A bacteriophage, or phage, is a virus that infects bacteria. It consists of an icosahedral (20-sided) head (transparent), which contains the genetic material (yellow strand), a tail (covered in spheres) and tail fibres (red). The tail fibres attach to the surface of a bacterium and then the tail injects the genetic material into the cell. The viral genetic material hijacks the bacterium's own cellular machinery, forcing it to produce more copies of the bacteriophage. When a sufficient number have been produced the phages exit the cell by lysis, killing it in the process.