Which type of virus primarily infects bacterial cells?

Bacteriophages are viruses specifically designed to infect bacterial cells. They exhibit a unique structure and life cycle that allows them to attach to bacteria, inject their genetic material, and subsequently hijack the bacterial machinery to produce more viral particles. This process can lead to the lysis (destruction) of the bacteria, making bacteriophages important tools in research and potential treatments for bacterial infections.

In contrast, retroviruses primarily infect animal cells and are known for their ability to reverse transcribe their RNA into DNA, which then integrates into the host's genome. Oncoviruses, which include certain types of retroviruses, are known to cause cancer in various animals, including humans, but they do not specifically target bacteria. Adenoviruses infect a wide range of hosts, primarily mammals, causing respiratory, gastrointestinal, and other infections in humans, but they too do not affect bacterial cells. Thus, bacteriophages stand out as the only type of virus that primarily targets and infects bacteria.