Bacteriophages or phages (pronounced fay-jehs) are bacterial viruses that only infect and replicate in bacteria. “Bacteriophage” itself literally translates to ‘eater of bacteria.’ Like all viruses, bacteriophages straddle the line between living and non-living, requiring bacterial cells for their reproduction. They do so with a cycle of cellular invasion, hijacking, replication, and propagation. 

Under the microscope, bacteriophages take on many shapes and sizes, but the most iconic structure looks like a cross between a spaceship and a spider. They have a protein capsid or ‘head’ housing the viral genome, a DNA injector tube or ‘body’ that pumps DNA into the bacterial cell, and tail fibers or ‘legs’ that latch onto the outer surface of the bacterial cell. 

There are more bacteriophages in the world than there are bacteria, in fact, bacteria are outnumbered ten to one and the bacteriophage are the most prevalent organisms in the world. Scientists estimate that there are around 1031 or ten nonillion bacteriophages on Earth. This means that bacteriophages are everywhere. They are on our skin, in our body, in the food that we eat, in the water that we drink, and in the air that we breathe. Because they only infect bacteria, bacteriophages are considered safe because they cannot infect people. 

Once inside the bacterial cell, bacteriophages hijack the bacterial machinery and command the bacterial cell to make more bacteriophages, typically dozens to hundreds at a time. The infected bacterial cell will succumb to overwhelming pressure and burst open, releasing new bacteriophage that can infect neighboring bacteria and repeat the cycle.