Scientists at Washington University School of Medicine in St. Louis say they have found definitive proof that some of the bacteria that plague women with urinary tract infections (UTIs) are entrenched inside human bladder cells.


The finding confirms a controversial revision of scientists model of how bacteria cause UTIs. Previously, most researchers assumed that the bacteria responsible for infections get into the bladder, but dont invade the individual cells that line the interior of the bladder.


Our animal model of UTIs has allowed us to make a number of predictions about human UTIs, but at the end of the day, we felt it was critical to show this in humans, and now weve done just that, says senior author Scott J. Hultgren, a professor in molecular microbiology.


The study findings appeared in the December issue of a publication called the Public Library of Science Medicine.


Fully understanding what bacteria do in the bladder is critical to developing better diagnoses and treatments for UTIs, Hultgren says. The bacterium Escherchia colibetter known just as E. coliis thought to be responsible for 80 percent to 90 percent of UTIs, which occur mainly in women and are one of the most common bacterial infections in the U.S. Scientists estimate that more than half of all women will experience a UTI in their lifetimes, and recurrent UTIs will affect 20 percent to 40 percent of those patients.


Recurrence is one of the biggest problems of UTIs, says Hultgren. Even though we have treatments that eliminate the acute symptoms, the fact that the disease keeps recurring in so many women tells me that we need to develop better treatments.


Prior to the work of Hultgren and his colleagues, most microbiologists and urologists believed that E. coli wasnt getting into bladder cells.


For example, there is a barrier in the bladder that prevents toxins and other things in your urine from leaking back into the body, says David Rosen, a student at the school and lead author of the paper. And it was thought that bacteria could not penetrate that barrier.


A biopsy could reveal the presence of bacteria in bladder cells, but taking a tissue sample in an infected bladder involves an unacceptable risk of allowing bacteria to spread into the bloodstream, a dangerous condition called sepsis.


Scientists also thought that if the bacteria were getting into bladder cells, they would replicate and spread rapidly, sometimes leading to sepsis. But after Hultgren first discovered that bacteria are able to invade bladder cells in 1998, he later found evidence in his animal model that bacteria could establish residence inside those cells. He showed that this process involved several behavioral changes that allow the bacteria to form communities known as biofilms. By working together, bacteria in biofilms build themselves into structures that are more firmly anchored in infected cells and are more resistant to immune system assaults and antibiotic treatments.


To prove that the model correlates with human infections, Rosen led an analysis of human urine samples sent from a clinic at the University of Washington, in Seattle. The 100 patients who gave samples either were suffering from an active infection or previously had suffered infections. Using an electron microscope and other methods, scientists found signs of bladder cell infection in a significant portion of the samples from patients with active urinary tract infections. These included cells enlarged by bacterial infection and shed from the lining of the bladder.


Also, Hultgrens experiments previously suggested that some bacteria progress to a filament-like shape when exiting out of the biofilm. Rosen was able to identify bacteria with that type of structure in 41 percent of samples from patients with symptomatic urinary tract infections.


Neither indicator was detected in urine from women who didnt have active infections. This was anticipated: Hultgrens animal model work suggests that when women are between episodes of symptomatic infection, E. coli may be in dormant phases where there would be little cause for bacteria or the cells they infect to be shed into the urine.