A virus that invades bacteria is called a bacteriophage, or simply a phage. Bacteriophages are a type of virus that specifically infects and replicates within bacteria, similar to how viruses infect and replicate within animal cells. They are very small, even compared to bacteria, and can only be observed using an electron microscope. Bacteriophages have the ability to infect and lyse specific bacterial host strains. They typically consist of a protein coat that encloses a DNA or RNA genome. Upon infection, a bacteriophage injects its genetic material into the host bacterium, essentially hijacking the bacterium's cellular machinery to produce more copies of the phage. The newly produced phages then exit the host cell, often causing the cell to burst (lyse) and release more phages into the environment. Bacteriophages are highly specific in their host range, meaning that they can only infect and replicate within certain types of bacteria.