What is the name for a virus that infects a bacteria?

A virus that infects a bacterium is called a bacteriophage, or simply a phage. The name combines the Greek words for “bacteria” and “to eat,” reflecting the way many phages destroy their bacterial hosts.

A bacteriophage attaches to specific receptors on a bacterial cell and injects its genetic material. In a lytic infection, the viral genes take over the cell’s machinery, produce new phages, and eventually cause the bacterium to burst. Some phages instead enter a lysogenic cycle, integrating their genetic material into the bacterial chromosome as a prophage and remaining dormant for a time.

Phages are extraordinarily abundant and diverse. They occur wherever bacteria live, including soil, oceans, sewage, and the human microbiome. Scientists have also studied them as possible tools against antibiotic-resistant infections, an approach known as phage therapy. Bacteriophages are not the same as antibiotics: antibiotics are chemical drugs, while phages are viruses that target particular bacterial hosts.