What term describes a virus that specifically infects bacteria?

The term that describes a virus that specifically infects bacteria is "bacteriophage." Bacteriophages, often referred to as phages, are a unique group of viruses that have evolved specifically to target bacterial cells. They attach to the surface of bacteria, inject their genetic material, and subsequently hijack the bacterial cellular machinery to replicate themselves. This characteristic makes bacteriophages crucial tools in both microbiology research and applications such as phage therapy, which is being explored as an alternative to antibiotics for treating bacterial infections.

In contrast, protozoans are unicellular organisms that are quite distinct from viruses, as they belong to a different domain of life and are not infectious agents targeting bacteria. Plasmids are small, circular pieces of DNA found in bacteria, which can carry genes such as those for antibiotic resistance but are not viruses themselves. Archaea refers to a separate domain of single-celled organisms that share certain similarities with bacteria but are distinct in their molecular characteristics and often inhabit extreme environments.