WASHINGTON — Silently, invisibly, vast miniature armies are waging a fight to the death on land and sea. ¶ The defenders are bacteria, the one-celled microbes that infest every cranny on Earth, from the sea floor to the human gut. The aggressors are a class of viruses known as bacteriophages — literally "bacteria eaters" — that slaughter their far-bigger foes.
"Every two days, half the bacteria on Earth are killed" by bacteriophages, says Dr. Vincent Fischetti, head of the Laboratory of Bacterial Pathogenesis at Rockefeller University in New York.
"Phages," as the viruses are known for short, are harmless to humans but can be enlisted in the fight against disease-causing germs and can perform other useful functions.
Many bacteria divide roughly every 20 minutes, so they can reproduce their population as rapidly as they are slain.
Biologists estimate that the world contains a thousand billion billion billion — that's a 1 followed by 30 zeroes — bacteria. Yet phages outnumber bacteria 10 to 1.
One way these ruthless little killers perform is by chewing up bacteria, such as the deadly Staphylococcus aureus, that resist most antibiotic drugs.
"Antibiotic resistance is a nightmare for infectious-disease specialists, who increasingly have to stand by and watch helplessly as bacteria dupe the drugs aimed at (stopping) them, and people die because no drugs work," according to Thomas Hausler, author of a recent book about phages, Virus vs. SuperBugs.
As an example of the utility of phages, the FDA in 2007 approved their use on ready-to-eat meats, to kill any bacteria.
Phages also are being used to treat open sores caused by diabetes and for soldiers whose wounds resist antibiotics, according to Dr. Randall Wolcott, head of the Southwest Regional Wound Care Center in Lubbock, Texas.
Viruses are the most numerous biological creations on Earth. They come in many shapes and sizes besides phages. Many are responsible for infectious diseases, from the common cold to AIDS.
Scientists disagree on whether viruses are alive, since they can't reproduce on their own but must hijack the genetic machinery of living cells. Phages use bacteria as factories to manufacture more of themselves.
When a phage bumps into a bacterium, it latches on to its surface and penetrates the cell wall. Once inside, it takes control of the bacterium's DNA to make hundreds of copies of itself. The bacterium soon dies, releasing a horde of baby viruses to find new victims.
In this way, phages kill bacteria without the use of antibiotic drugs.
Scientists first realized phages' therapeutic potential during World War I. Phages continued to be used in Russia and Eastern Europe, but interest faded in the West after penicillin and other antibiotics were discovered.
The rise of antibiotic resistance has revived phage research. But there is a downside to phages:
Some bacteria are fighting back by developing resistance to their little persecutors. For example, some bacteria have learned to change their surface structures so the phages cannot get inside, according to Peter Fineran, an expert at the University of Cambridge, England.