In a study appearing Friday in the journal Science, scientists at Washington University in St. Louis report using an electron microscope to discover that E. coli bacteria form a biofilm inside cells of the bladder cells of mice.
This biofilm is composed of bacteria unified into a colony to resist attack, said Dr. Joseph J. Palermo, a Washington University researcher and a co-author of the study.
"The bacteria rest in a matrix like eggs in a carton," said Palermo. He said this is the first time that a biofilm structure has been found within a cell, and the discovery explains why many patients are unable to ever become completely free of urinary tract infections.
"In a biofilm, thousands and thousands of bacteria work together as sort of a multicellular organism," said Gregory G. Anderson, a co-author of the study.
Anderson said the biofilm "is a slimy type of mesh" similar to the slick coating often found on submerged rocks in a stream or pool of water.
Although the study was of mouse bladders, Palermo said the animal is a commonly studied model for urinary tract disease because the tissue, cells and infection response of the rodent bladder are very similar to that of humans.
Dr. Josephine P. Briggs, head of group studying urinary tract disease at the National Institute of Diabetes and Kidney Research, one of the National Institutes of Health, said the discovery of an E. coli biofilm is "very intriguing." She said it explains why some bladder infections are so difficult to control in some patients.
"This study demonstrates this in mice, but there is no reason to think the process is not occurring in people," said Briggs. "That needs to be documented, but it is very likely."
If biofilm formation is confirmed in humans, she said, then it adds a new sense of urgency to the need to develop alternate ways to treat stubborn urinary tract infections.
The Washington University researchers said their studies show that individual E. coli bacteria assume different roles within the biofilm, acting like members of a multi-cell organism. Bacteria on the edge of the biofilm can burst out of the host cell and colonize other cells within the bladder wall.
Because the bacteria are within the cells of the bladder, they often are not detected by routine medical tests, said Palermo.
"When you check a urine sample for the presence of bacteria, all you are looking for are free floating bacteria," he said. "If there are bacteria in the bladder tissue itself, you are not going to pick them up. Having sterile urine doesn't really give you a picture of what the bacteria state of the bladder is. It makes diagnosis more difficult."
Recurring or highly resistant urinary tract infections are a major medical problem, particularly among women. The infections cause frequent and painful urination, fever and can lead to more dangerous kidney infections.
About 8 million urinary tract infections are diagnosed annually, second only to respiratory infections in the United States.
Antibiotics usually knock out the infections, but for many it becomes a problem returning time after time.
By Paul Recer