Tis the season to be getting the cold and flu. But is it possible for the bacteria and viruses that infect us so easily to get sick themselves?

In 1917, a microbiologist working at the Pasteur Institute in Paris discovered what he described as an invisible, antagonistic microbe that had a parasitic relationship with bacteria. He called it a bacteriophage (from phagein, "to eat"), a virus that infects bacteria.

Bacteria Killers

Bacteriophages are simple organisms, usually just a strands or two of RNA or DNA enclosed in a protein hull with a tail attached. What they lack in sophisticated design, they make for in numbers: they're thought to be some of the the most widely distributed and diverse organisms on Earth. They can be found anywhere that bacteria live, from dirt, to oceans—where they may be infecting up to 70 percent of all marine bacteria—to our own intestines.

To enter their bacterial hosts, bacteriophages attach to receptors on the surface of bacteria (which can be various molecules or organic compounds, but a particular bacteriophage specializes in certain receptors) and are either drawn in to the cell or inject their genetic material into it. Either way, the end result is that the bacteriophage's genetic material takes over the bacterium's cellular machinery and forces it to produce more bacteriophages, which then spread out and infect other bacteria. It's all the gruesome drama of a nature show played out on a microbe-sized stage.

Figuring that the enemy of our enemy is our friend, scientists put bacteriophages to use as anti-bacterial agents. "Phage therapy" was abandoned in most places a few years later, when antibiotics - which were easier to manufacture, store and use - were discovered. Today, bacteriophages are still used to kill bacteria on food products, plants, and medical devices.

There's a flipside to bacteriophages' usefulness, though. They don't discriminate between "good" and "bad" bacteria like we do, and phage contamination of bacteria being cultivated for use in probiotic dairy products, for example, can bring things to a halt and cost the manufacturer time and money.

Virus Infectors

In 2008, researchers from the Universite de la Mediterranee in Marseille, France, identified an exceptionally large virus infecting an amoeba. They dubbed it mamavirus, and soon discovered another layer to the microscopic nesting dolls. The amoeba's virus was itself infected by a much smaller virus.

Sputnik, as the researchers called it, was the first member of a new class of viruses that scientists call virophages, viruses that infect other viruses. Sputnik has trouble multiplying without it preferred viral host, but once an amoeba is infected with the mamavirus, Sputnik hijacks the mama's cellular machinery and multiplies at its expense, producing more Sputniks while the mamavirus' own replicated particles assemble abnormally. The mechanics of it are fairly similar to what the mamavirus does to the amoeba. In effect, the virus is getting a taste of its own medicine.