Washington, Jul 9 (IANS): Bugs causing serious urinary tract infections stay ahead of the immune system by filching copper to prevent the metal from being used against them, says a study.

Copper has been known as a potent weapon against infection for centuries. Blocking this thievery with a drug may significantly improve patients' chances of warding off infections, according to Washington University School of Medicine researchers in St. Louis.

In the US alone, annual treatment costs for urinary tract infections are estimated to run as high as $1.6 billion. Most urinary tract infections (UTI) are caused by Escherichia coli (E. coli), the journal Nature Chemical Biology reported.

"While some patients are able to clear these infections without issue, in others the infection persists or recurs despite antibiotic therapy," says senior study author Jeff Henderson, assistant professor of medicine and of molecular microbiology at Washington.

"In some cases, the infection spreads to the kidney or the blood and becomes life threatening. We've been investigating what's different about the bacteria that cause these more trouble some infections," Henderson said, according to a university statement.

Scientists have known for years that E. coli makes a molecule called yersiniabactin that takes iron from host cells. The bacteria need the iron to grow and reproduce.

Researchers placed yersiniabactin in urine samples from healthy patients. They found the molecule bound iron as expected but also picked up copper. Next, they conducted the same analysis in samples from urinary tract infections, treated at the University of Washington in Seattle.

"We found copper bound to yersiniabactin in nearly every patient whose bacteria made the molecule," Henderson said. "Yersiniabactin was often bound to copper more than it was to iron." When researchers put E. coli in the same test tube with copper, the bacteria that made yersiniabactin were more likely to survive.

Modern researchers have two explanations for copper's antimicrobial effects: the metal can stimulate production of other chemically reactive molecules that damage bacteria; and it is also directly toxic to the bacteria.