Bacteriophages attacking bacteria, transmission electron micrograph (TEM) of bacteriophage virus particles (virions, green) attacking a bacterial cell (orange). A bacteriophage is a virus that infects bacteria. It consists of an icosahedral (20-sided) head, which contains the genetic material, a tail and tail fibres, which fix it to a specific receptor site. Once attached to a bacterium, the bacteriophage injects its DNA (deoxyribonucleic acid) and the bacterium's cellular mechanisms are used to produce more bacteriophages.