Research News

Even in the absence of infection, urological medical devices may harbor more — and more complex — bacteria than previously understood, according to findings from two recent studies. The studies, performed in the laboratory of Aaron Miller, PhD, Assistant Staff in Cardiovascular and Metabolic Sciences, report that thriving communities of bacteria can colonize the surfaces of medical devices implanted along the urinary tract. Together, these papers raise new questions about potential pathways to infection.

The two papers, published in January and May of 2023, investigated how microbes colonize artificial urinary sphincters (AUSs) and stents, respectively. AUSs are commonly used to treat forms of urinary incontinence, while stents are often used to help drain the upper urinary tract in cases of ureteral obstruction or to help with post-surgical wound healing.

“Historically, it was thought that the devices were devoid of microbes in the absence of infection, but recent evidence involving urinary catheters has shown that even noninfected devices may harbor bacteria,” says the first author of both studies, Glenn Werneburg, MD, PhD, a fellow in the Department of Urology. “Our findings support the hypothesis that these findings aren’t unique to catheters. Bacteria can, and do, asymptomatically colonize other medical devices throughout the urinary tract.”

The main way hospitals and device manufactures work to prevent device-associated infections is to try and block bacteria from colonizing a device altogether. Devices are manufactured with special coatings that are physically harder for microbes to stick to. Many devices are also pre-treated with antibiotics, which runs the risk of increasing antibiotic resistance among bacteria. Dr. Miller, senior author on the study, states that these measures, while important, may only be targeting part of the problem.

"Our findings support the hypothesis that bacteria can and do colonize these devices all the time, without any issues for the host. The presence of bacteria isn’t the true problem. It’s how the bacteria switch from coexisting harmlessly with the patient, to causing a harmful symptomatic infection.”

What was done

Device-associated infections comprise the majority of hospital-acquired infections. A large proportion of these infections occur in the urinary tract. Co-author and urologist Scott Lundy, MD, PhD, says that device-associated infections can be devastating.

 “The device must be removed and may not be able to be replaced immediately. Any benefit of the implant will be lost without placement of a new device. Patients who struggled with incontinence will lose any control an artificial urinary sphincter had granted.”

In both studies, researchers obtained medical devices (AUSs and stents) that had been removed from patients in the clinic. Some of these patients were diagnosed with a device-associated infection, while others were classified as infection-free. The researchers analyzed these devices to investigate the presence of bacteria and to characterize the species and characteristics of any bacterial communities present.

Virtually all medical devices tested, regardless of the type of device, had thriving communities of microbes living and colonizing on their surfaces. Bacteria were present even in patients who did not experience any symptoms of infection. Researchers discovered that the types of bacteria on the devices did not dictate whether a patient experienced discomfort as much as the way the bacteria metabolized their “food.” These results, says Dr. Miller, indicate that the processes driving device-associated infections may be more complicated than previously thought.

Dr. Werneburg says that follow up could lead to new information about the transition from asymptomatic to infected states. This new information, he claims, can inform the next generation of medical device coatings and materials.

“We are now looking into the different metabolic profiles of bacteria colonizing infection and noninfection-associated devices, to see whether they might be conducive to or protective against infection,” he notes.

“This study truly changes the paradigm of infections and suggests we need to work smarter, not harder, to prevent infections,” concludes Dr. Lundy. “More antibiotics is not always better. We are optimistic that other targeted interventions may be available in the future.”

This article was partially adapted from Consult QD.