Doctors are finding it more and more difficult to treat a common infection because the bacteria that cause it are becoming increasingly resistant to antibiotics. Now, new research may have uncovered one reason for the pervasiveness of these superbugs.

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New research finds drug resistant Escherichia coli in the guts of symptomless women.

Urinary tract infections (UTIs) arise when bacteria enter the urinary tract. It is one of the most common infections to affect people.

Although any part of the urinary tract can become infected, UTIs most commonly occur in the bladder.

UTIs are more common in girls and women than in boys and men.

The urethra, or urine pipe, is shorter and nearer to the anus in females, which allows germs from the gut to reach various parts of the female urinary tract more easily.

The main cause of UTI in women is the bacterium Escherichia coli. Drug resistant strains of E.coli are spreading widely, causing doctors to think twice about which antibiotics to prescribe.

Resistant UTI bacteria in uninfected women

In the new Clinical Infectious Diseases study, researchers tested stool samples from more than 1,000 healthy women who were free of UTI symptoms. The women were from the Puget Sound area of Washington.

The tests revealed that 8.8% of the women were carrying fluoroquinolone resistant strains of E. coli in their guts.

Doctors frequently prescribe fluoroquinolones for the treatment of UTIs. The researchers note that, although there have been efforts to limit the use of these antibiotics, resistant strains of bacteria are spreading widely.

In addition, the researchers found that most of the fluoroquinolone resistant E. coli bacteria also belonged to two widespread, multidrug resistant strains that are responsible for most hard-to-treat urinary and blood infections.

The researchers also tested urine samples that the women had given at the same times as the stool samples.

These tests revealed that more than one-third of the women with fluoroquinolone resistant E. coli gut bacteria also had E.coli in their urine. Of these, almost 77% had fluoroquinolone resistant strains that matched those of their stool samples.

Of the women, 45 also gave permission for the team to track their medical records. These showed that 7% of them went on to receive diagnoses of UTI some 3 months later.

'Superior, persistent gut colonizers'

The study authors describe the two drug resistant strains of E.coli that they found as "superior gut colonizers" that "tend to persist there."

"They can also show up," they note, "at an unusually high rate, in the urine of healthy women who did not have a documented urinary tract infection diagnosis at the time of sample testing."

"Both phenomena appear to be interconnected," they add.

The findings could have a number of clinical implications concerning the care and control of infections, says senior study author Dr. Evgeni V. Sokurenko, a professor of microbiology at the University of Washington School of Medicine, in Seattle.

He suggests that testing for multidrug resistant bacteria in the gut could help doctors predict how strongly a woman's infection might resist drug treatment.

It might also be necessary to have a policy about what doctors should do if they find resistant bacteria in the urine of patients who have no symptoms of infection.

Ridding carriers of widespread resistant strains could potentially reduce their risk of multidrug resistant infections, Dr. Sokurenko suggests. It could also reduce the risk of such infections in those with whom they come into contact.

Dr. Sokurenko is a major shareholder of ID Genomics, a company that specializes in matching a specific drug to the germ behind an infection. He has also applied for patents for tests that detect strains of E.coli.