Illustration of bacteriophages (purple) infecting a bacterial cell (green). Bacteriophages, or phages, infect a bacterium by attaching to its surface and injecting genetic material 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. These phages may traverse the gut cell wall (pink, right) and enter the bloodstream.