Bacteriophages leaving host cell. Computer illustration showing bacteriophage virus particles (virions, small, purple) bursting out of their host bacterium (round). Bacteriophages are viruses that infect bacteria. They have tail fibres (leg-like), which fix them to a specific receptor site on the bacterium. They then inject their DNA (deoxyribonucleic acid), into the host, which makes the bacteria manufacture more copies of the virus. When mature, these clones burst out of the host bacterial cell, as shown here.