Bacteriophage T4 viruses. 3D computer illustration of multiple T4 bacteriophage viruses. A bacteriophage, or phage, is a virus that infects bacteria. Enterobacteria T4 infects E. coli bacteria. It consists of an icosahedral (20-sided) head, which contains the genetic material, a tail (cylindrical) and tail fibres (leg-like). The tail fibres attach to the surface of the bacterium and the tail injects a DNA (deoxyribonucleic acid) strand into the cell. The viral genetic material then 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 burst out of the cell, killing it in the process.