Bacteriophages—viruses that infect bacteria before multiplying within them—exist on Earth in numbers greater than all other living organisms combined.

Findings

Additional insights we found via Kurzgesagt – In a Nutshell

Bacteriophages can be considered the deadliest agents on the planet, killing up to 40% of all ocean bacteria daily, but there's little collateral damage to human cells or other non-target bacteria because each phage is specialized to target only a specific type of bacterium or bacterial group.
Bacteriophages possess an icosahedral "head"—a 20-sided shape—housing genetic material, which often sits atop a long tail ending in fibers that resemble legs, and this tail delivers the genetic material into bacteria like a syringe.
A bacteriophage's genetic material can hijack a bacterium's cellular processes, forcing it to produce more phages, which burst out of the bacterium with the aid of an endolysin, an enzyme that destroys bacterial cell walls.
Unlike some antibiotics, which kill a broad range of bacteria by destroying cell walls or interfering with protein synthesis and DNA replication, bacteriophages attack only specific bacteria, allowing scientists to use phages for more targeted treatments without contributing to growing antibiotic resistance.
Phage therapy is not without risks, including septic shock, which is also a concern with antibiotics. As bacteria die, toxic materials are often released, and this can trigger an overwhelming immune response that can result in organ failure.