CORR Insights®: Does Suture Type Influence Bacterial Retention and Biofilm Formation After Irrigation in a Mouse Model?

Where Are We Now?

One area of research that has grown substantially in the last decade is the focus on value in health care. In our specialty, joint arthroplasty research currently leads the way in this area largely due to infection-related complications and the need for cost containment, particularly as bundled-payment systems are put into action. Despite our best efforts preventing, diagnosing, and treating periprosthetic joint infection (PJI) during the past decade, we have not lowered the risk of PJI [7]. Therefore, surgeons should explore the infection risks associated with our common surgical practices—down to the most basic of steps—in order to identify the ways we can mitigate such risks.

The current study by Markel and colleagues [8] reproduced a clinical scenario in a mouse model in which an acute postoperative infection underwent simple wound irrigation. The authors then compared bacterial adherence and biofilm formation before and after irrigation on commonly used sutures (braided and monofilament) in joint arthroplasty wound closures. Although intended for the joint arthroplasty audience, the current study’s results are important to all surgeons who use these types of sutures.

Markel and colleagues found that braided sutures retain and harbor more bacteria than monofilament barbed sutures despite being subjected to irrigation [8]. These results, coupled with the existing data [5, 9, 10], allow us to draw two basic conclusions: (1) Bacterial adherence is greater on braided sutures compared to monofilament sutures, and (2) bacterial adherence to high-tensile strength sutures correlates with suture strength [10]. These observations can help guide surgeons in appropriate suture selection to accomplish the intended surgical goal.

Where Do We Need To Go?

In an era where value is the heavy focus, we should explore all the ways we can mitigate surgical-site infection (SSI) risk. Common surgical practices, like selecting a suture that has less bacterial adherence and lower bacteria biofilm formation, and ensuring that we have removed all the retained suture during a débridement procedure, may minimize the risk of SSI.

To reduce SSI risk still further, we must better understand bacterial biofilms, determine the ideal methods to eradicate them, and accelerate the implementation of those methods into clinical practice. Implanted orthopaedic devices and sutures, surrounded by moist, soft tissues and hematomas, create a solid-liquid interface in which contaminated biofilms can thrive in as little as a few hours. Bacteria within a biofilm can be difficult to treat because they exhibit a different phenotype and are metabolically distinct from their planktonic form, which may decrease the efficacy of certain antibiotics. In addition, the immune system seems to have difficulty with clearing bacteria when they have established a biofilm [2].

Bacteria in biofilms further differ from planktonic bacteria in that those in biofilm more-easily transfer genetic material and resistance genes; we therefore need to focus research on developing antibiotics that are effective in this setting. Acyldepsipeptide (ADEP) antibiotics are one example, where one of its derivatives, ADEP4, shows promise [3]. D-amino acids or other agents found to trigger active dispersal of biofilms should also be studied in greater detail [13]. While these newer agents may prove effective in current models, further research is needed to confirm their effectiveness in the clinical setting.

For now, the most-effective measure to eradicate bacteria biofilm is to perform an adequate débridement and remove the implant (or suture) harboring the biofilm. It would be helpful to have antibiotics that can treat bacteria when those mechanical approaches fall short or are not possible, but as of now, such antibiotics are not available.

How Do We Get There?

We generally combat infection with antibiotics, and while they are commonly prescribed systemically, they are being increasingly used locally as a preventive measure. Local antibiotic powder may be an effective adjunct, and it could be used in certain fractures should a SSI occur [11, 15]. Preliminary results are generally favorable when surgeons use local antibiotic powder in addition to traditional algorithms to manage infected total joint arthroplasty [6], though some have raised safety questions when it is used for primary total joint arthroplasty [4]. Large randomized trials certainly are called for and in some patient populations, are currently underway [12]. While local vancomycin may not be the “holy grail” in SSI prevention, its use has increased because it is relatively inexpensive and does not require a carrier. More importantly, it achieves high concentrations in the surgical wound, well above the Minimum Inhibitory Concentration for common pathogens, without the concern for systemic toxicity [1]. Because vancomycin does not cover all common pathogens, the use of other topical antibiotics that are also effective against biofilms, such as rifampin which has demonstrated promise in an animal model, [14] should be explored with clinical trials initially focusing on high-risk patient populations.

When using antibiotics, surgeons are often concerned about the development of bacteria resistance. ADEP antibiotics can kill bacteria by deregulating the ClpP protease in bacteria, and rifampin, an RNA polymerase inhibitor, is also effective against biofilms, particularly both rapidly dividing and stationary-phase bacteria. Still, concerns that resistance can develop for both are well founded. For example, staphylococci easily develop a single point mutation in the DNA-dependent RNA polymerase when bacterial concentrations are high, ultimately rendering the rifampin ineffective when used in isolation. In fact, 1 in 10⁷ colony-forming units of staphylococci have naturally occurring resistance to rifampin [16]. If these antibiotics are used in the clinical setting, combination therapies (using two antibiotics that attack bacteria via two different mechanisms) will likely be needed to improve efficacy and minimize the development of antibiotic resistance. By partnering with basic scientists and our infectious disease colleagues, orthopaedic surgeons can work towards developing a standardized musculoskeletal infection model, testing its interventions, and rapidly translated it into clinical practice.