In order to safeguard patients from microorganisms that rarely sicken healthy people but can be fatal for susceptible patients already hospitalized with serious illnesses, hospitals maintain tight cleanliness and sanitation practices.
Every year, illnesses that they contract after being hospitalized to a hospital in the United States cause close to 100,000 deaths. But despite significant efforts to prevent infections, new bacterial strains continue to appear apparently out of nowhere and infect patients in hospitals all over the world.
A surprising source of these bacteria has been identified by Washington University School of Medicine researchers in St. Louis: the hospitalized patients themselves. Urinary tract infections (UTIs) can develop after sterile tubes, known as catheters, are placed into the urinary tract, even if germs are not initially visible in the bladder, the researchers found while studying mice.
These tubes are frequently used in hospitals to empty surgical patients’ bladders. In the mice, inserting the tubes activated dormant Acinetobacter baumannii (A. baumannii) bacteria hidden in bladder cells, triggering them to emerge, multiply and cause UTIs, the researchers said.
The research, which was released on January 11 (2023) in Science Translational Medicine, suggests that checking patients for latent reservoirs of harmful bacteria could support current infection-control strategies and help avoid fatal illnesses.
“You could sterilize the whole hospital, and you would still have new strains of A. baumannii popping up,” said co-senior author Mario Feldman, PhD, a professor of molecular microbiology. “Cleaning is just not enough, and nobody really knows why. This study shows that patients may be unwittingly carrying the bacteria into the hospital themselves, and that has implications for infection control. If someone has a planned surgery and is going to be catheterized, we could try to determine whether the patient is carrying the bacteria and cure that person of it before the surgery. Ideally, that would reduce the chances of developing one of these life-threatening infections.”
The bacteria must have been there all along, hiding inside bladder cells until the catheter was introduced. Catheterization induces inflammation, and inflammation causes the reservoir to activate, and the infection blooms.
Scott J. Hultgren
Hospitalized patients are at serious risk from A. baumannii, which frequently causes UTIs in those using catheters, pneumonia in those using ventilators, and bloodstream infections in those using central-line catheters in their veins. Such infections are difficult to cure and easily develop into fatal ones since the bacteria are notoriously resistant to a wide variety of medications.
Feldman teamed up with co-senior author Scott J. Hultgren, PhD, the Helen L. Stoever Professor of Molecular Microbiology and an expert on UTIs, to investigate why so many A. baumannii UTIs develop after people receive catheters.
Most UTIs among otherwise healthy people are caused by the bacterium Escherichia coli (E. coli). According to research, E. coli can remain dormant in bladder cells for months after a UTI appears to be under control before resurfacing to produce another infection.
Feldman and Hultgren along with co-first authors Jennie E. Hazen, a graduate student, and Gisela Di Venanzio, PhD, an instructor in molecular microbiology investigated whether A. baumannii can hide inside cells like E. coli can. They studied mice with UTIs caused by A. baumannii. They used mice with weakened immune systems because, like people, healthy mice can fight off A. baumannii.
The researchers implanted catheters into the mice’s urinary tracts using a sterile approach after the illnesses had cleared up and there had been no germs seen in the mice’s urine for two months. Within 24 hours, about half of the mice developed UTIs caused by the same strain of A. baumannii as the initial infection.
“The bacteria must have been there all along, hiding inside bladder cells until the catheter was introduced,” Hultgren said. “Catheterization induces inflammation, and inflammation causes the reservoir to activate, and the infection blooms.”
Since A. baumannii rarely causes symptoms in otherwise healthy people, many people who carry the bacteria may never know they’re infected, the researchers said. As part of this study, the researchers searched the scientific literature and discovered that about 2% of healthy people carry A. baumannii in their urine.
“I wouldn’t put much weight on the precise percentage, but I think we can say with certainty that some percentage of the population is walking around with A. baumannii,” Feldman said. “As long as they’re basically healthy, it doesn’t cause any problems, but once they’re hospitalized, it’s a different matter. This changes how we think about infection control. We can start considering how to check if patients already have Acinetobacter before they receive certain types of treatment; how we can get rid of it; and if other bacteria that cause deadly outbreaks in hospitals, such as Klebsiella, hide in the body in the same way. That’s what we’re working on figuring out now.”
