Common type of hospital-associated infections can be prevented with vaccine

Washington University School of Medicine in St. LouisSep 18 2014

The most common type of hospital-associated infection may be preventable with a vaccine, new research in mice suggests.

The experimental vaccine, developed by researchers at Washington University School of Medicine in St. Louis, prevented urinary tract infections associated with catheters, the tubes used in hospitals and other care facilities to drain urine from a patient's bladder.

Each day a catheter is present in the urethra and the bladder, the risk of urinary tract infection increases. Nearly every patient who has a catheter for more than 30 days acquires a urinary tract infection. The infections make urination painful and can damage the bladder. If untreated, bacteria can cross into the bloodstream and cause sepsis, a potentially life-threatening complication.

"Catheter-associated urinary tract infections are very common," said first author Ana Lidia Flores-Mireles, PhD, a postdoctoral research associate at the School of Medicine. "Antibiotic resistance is increasing rapidly in the bacteria that cause these infections, so developing new treatments is a priority."

The study is available online Sept. 17 in Science Translational Medicine.

Manufacturers typically coat catheters with antibiotics to reduce the risk of infection. But Flores-Mireles and her colleagues in the laboratory of Scott Hultgren, PhD, showed that inserting catheters into the bladder provokes an inflammatory response that results in the catheter being covered with fibrinogen, a blood-clotting protein.

Fibrinogen shields bacteria from the antibiotics and provides bacteria with a landing pad to adhere to and food to consume as they establish an infection, the research revealed.

"The bacteria use long, thin hairs known as pili to anchor themselves to the fibrinogen, and then they can start to form biofilms, which are slimy coatings on the surface of the catheter composed of many bacteria," said co-author Michael Caparon Jr., PhD, professor of molecular microbiology. "The biofilms protect the bacteria from antibiotics and immune cells, further prevent them from being washed from the body by the flow of urine, and make it possible for bacteria to seed the lining of the bladder with infections."

The urethra and bladder of a mouse are too small to insert a full catheter into, but the scientists showed that surgically implanting a small segment of catheter into the bladder via the urethra increased vulnerability to infection in a similar fashion.

Working with Enterococcus faecalis, a common cause of catheter-associated urinary tract infections, Flores-Mireles showed that a protein on the end of the pili, EbpA, binds to fibrinogen and makes it possible for the bacteria to begin forming biofilms.

When Flores-Mireles prevented the bacteria from making EbpA, they couldn't start infections.

"This protein is like the anchor of a boat," she said. "Without the anchor, the infection is at the mercy of the waves and gets washed away."

Next, the researchers injected the mice with a vaccine containing EbpA. The vaccine caused the animal's immune systems to produce antibodies that blocked EbpA and stopped the infectious process.

The scientists are testing to see if the vaccine helps mice clear established infections of E. faecalis. They also are working to develop a monoclonal antibody that blocks EbpA to prevent catheter-associated infections in the urinary tract and elsewhere in the body.

"We took a closer look at this protein and found that one-half of it is essential for binding to fibrinogen to induce infections," Flores-Mireles said. "The segment of genetic code that makes this part of the protein is also found in the genes of many other bacteria that cause urinary tract infections, so a vaccine, antibody or drug that blocks this part of the protein may help prevent other infections linked to catheters in the urinary tract and in other parts of the body."

The research was based at Washington University's Center for Women's Infectious Disease Research, which is directed by Hultgren, the Helen L. Stoever Professor of Molecular Microbiology.