Transmission electron micrograph (TEM) of Escherichia coli bacterial cells infected by T4 bacteriophages (red dots). A bacteriophage, or phage, is a virus that infects bacteria. T4 bacteriophages infect E. coli bacteria. They have no reproductive machinery and rely on the apparatus of bacteria in order to replicate. Several phages are seen approaching E.coli cells. A phage can use its tail fibres to inject DNA (deoxyribonucleic acid) strands into a cell. This viral genetic material could then hijack 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. Magnification: x15,748 when printed at 10 centimetres wide.