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What You Should Know About Biofilm And Implants

Given the challenges of biofilm-related infections with implants, these authors discuss the limitations of perioperative prophylaxis, the combination of staged procedures with antibiotic recommendations as well as the potential and risks of emerging technologies to remove or prevent biofilm formation on surfaces.  

The term “superbug” was in the national spotlight again earlier this year after an outbreak of a carbapenem-resistant Enterobacteriaceae (CRE) infected seven patients at a UCLA hospital with two deaths linked to the superbug and nearly 180 patients who may have been exposed. Researchers suspected the infection transmitted through instrumentation that physicians used during routine endoscopy procedures. Though healthcare personnel disinfect these instruments between cases, they are apparently difficult to clean fully due to their design and growing resistance by bacteria.

One of the reasons these superbugs exist is through the mechanism of biofilms, which are highly resistant to normal therapies. Studies have shown that common biocides used in hospital cleaning protocols are not effective in decontamination of biofilm-laden surfaces with colonies of bacteria such as methicillin-resistant Staphylococcus aureus (MRSA), Pseudomonas aeruginosa, E. coli and Candida spp.1

Approximately 13 million Americans annually suffer microbial infections with biofilm involvement.2 The Centers for Disease Control and Prevention (CDC) and the National Institutes of Health (NIH) estimate that biofilm phenotype bacteria cause 65 to 80 percent of all human infectious disease.2 Others cite this rate as being closer to 99 percent with Staphylococcus species the most common biofilm-forming bacteria and Staphylococcus aureus, Staphylococcus epidermis and Pseudomonas aeruginosa making up close to 75 percent of all biofilms found on medical devices.3

These infections are expensive. The cost of implant failure includes additional surgeries, prolonged hospitalization, rehabilitation, antibiotic therapy and puts a prosthetic joint infection at estimates upward of $50,000 to $116,000.4,5

What Makes Up A Biofilm?
Van Leeuwenhoek first described the biofilm concept more than 300 years ago and to this day it remains as complex a problem.6 Biofilms are an assembly of bacteria in complex communities irreversibly bound to living and non-living materials, akin to plaque buildup on your teeth or algae on a rock.7,8 Not all bacteria attached to a surface meet the definition of biofilm.1

As the initial adhered bacteria multiply, they secrete and enclose themselves in an exopolysaccharide (extracellular polymeric substance) matrix composed of polysaccharides (the “glycocalyx”), DNA and proteins.3 The matrix attaches itself to biomaterials through flagella and pili appendage structures.8 The interior contains a heterogeneous mixture of bacterial microcolonies, proteins and nutrients of varying cells, species and concentrations.8 These microcolonies exist in active and dormant states, exchange genes and communicate through quorum sensing or cell-to-cell signaling between bacterium of the same or different species, or the host.2,8 This signaling, unique to biofilms, is involved in activation-deactivation of the colonies and genetic differentiation in order to continually adapt to the internal and external biofilm environment to aid in resistance and longevity.2,8

There are several factors responsible for biofilm resistance, including restricted penetration of antibacterial agents into the biofilm interior, decreased growth rate and quiescent states, and the expression of resistance genes.9 These protection methods allow the bacteria to have a reduced susceptibility and exposure to dehydration, antibiotics, phagocytosis and acids, allowing them to exist for long durations.

The strategy of restriction of penetration first starts with the extracellular polymeric substance layer, protecting against small and large molecule diffusion. Authors have proposed that these tactics result in biofilms having a higher minimum inhibitory concentration (MIC) than the same microbe that is not in biofilm form.9 The biofilm is resilient and infection can relapse once the local antibiotic concentration drops.

Biofilm And Implants: ‘A Race To The Surface’
Gristina coined the idea of a “race to the surface” in 1987 in relation to biomaterials acting as inert, virgin foreign bodies upon human implantation.10 The theory pertains to the concept of healthy host tissues competing against microorganisms in a race to attach to and inoculate available surfaces, such as biomaterials (plates, screws, wires, joint prosthesis, etc). If host tissues integrate first, the surface can be defended and is less available for bacterial colonization. However, if the microorganism wins out, then biofilms can aggregate.

Biofilm adherence to a surface takes place in steps. First is the formation of a conditioning film on the surface of the biomaterial, occurring seconds after exposure. This film allows for microorganisms to adhere to the biomaterial surface. At this point, the microorganisms are reversibly attached. Next is the production of the extracellular polymeric substance and adherence by the glycocalyx. With this step, the organisms become irreversibly attached. This glycocalyx not only acts as the anchor but is also a protection layer from antibiotics. The organisms adhere and multiply, creating a thick film outer layer. These organisms also have a lowered metabolic or quiescent state, reducing antibiotic sensitivity and creating a difficulty in detection through microbiological culturing. Bacteria in the periphery of the expanding biofilm may detach, resulting in an infectious process.11

Understanding The Obstacles With Bacterial Seeding On Implants
Bacterial seeding on implants can originate from multiple sources. It can occur through the skin during implantation, via airborne organisms in the operating room or by hematogenous spread from a secondary source.11 These colonies can be monomicrobial or polymicrobial, and are frequently infected with S. aureus (generally found on metallic implants and in acute infections), coagulase-negative Staphylococcus/S. epidermis (generally found on polymer implant components and in chronic infections), beta-hemolytic Streptococci, and aerobic Gram negative rods.4,8,10-12

Due to the trauma from surgery, host immune defenses are diminished and a local acute inflammatory cascade occurs. This can persist as chronic inflammation due to the biomaterial not being completely chemically inert to the host environment in conjunction with any microorganisms in and around the implant. This can result in osteolysis and aseptic loosening, creating a site where microorganisms may seed, where host defenses are diminished and infection occurs.6,11

When physicians use biomaterials in surgery and they become colonized and ultimately infected, the treatment is much different than when soft tissue alone is involved. Many times, these infections are resistant bacteria and require removal of the implant.

So why is it so hard to get rid of a biofilm on an implant? The ability of biofilms to resist antibiotics is time-dependent with greater resistance to the therapy as time elapses, even after just one week of colonization.4,13 Inadequate sterilization or therapy of just antibiotics alone (no debridement) can actually be detrimental and increase the resistance of the biofilm. Often patients receive courses of intravenous antibiotics prior to the decision for debridement or implant removal. Studies have shown that after only one week of inadequate antibiotic therapy (with no surgery), these bacteria can develop a resistance.4 Biofilms have the potential to be 1,000 times more resistant to antibiotics in comparison to the single bacterial cell.4

A decreased growth rate of the biofilm also aids in resistance. Most antibacterial drugs are more effective in the killing of rapidly growing cells. In biofilms, while the exterior cells are usually more metabolically active, the deeper, interior cells are often in a state of decreased growth (secondary to a local environment of low nutrient concentrations) or dormancy, protected from both antibiotics and the host’s immune defenses.2,13

Additionally, different characteristics of the biomaterial can increase adhesion levels. Implants with rougher surfaces have decreased shear forces and greater surface area for adherence.8 Researchers have found that organisms attach to hydrophobic surfaces at higher rates.4,8

Realistically, one cannot always remove an implant immediately in the face of infection as these implants are giving stability to the bony architecture. With the goal of eradicating the infection, infectious disease doctors will recommend culture-driven IV antibiotics and complete removal of the hardware. Meanwhile, the surgeon may not want to remove the hardware immediately as it could destabilize the operative site and put the extremity in jeopardy. Once one has removed the implant and loses stability, either after traumatic fracture or elective joint replacement, morbidity to the limb increases. External fixation is an option when one must remove implants and stability is required, but this does not come without risk as authors have cited pin site infection rates of up to 96.6 percent.14 From a reconstructive surgery perspective, it is easier to treat an infected union versus an infected non-union.15

When there is an infection involving an implant, one should perform surgery whether it is irrigation and debridement of bone and soft tissue, the use of antibiotic-coated polymethylmethacrylate (PMMA) cement spacers, or an implant holiday or exchange. Lack of surgical intervention breeds resistance by these biofilm organisms. Debridement, in addition to implant removal, is important because in biomaterial infections, compromised tissue and bone also act as reservoirs for the biofilm.10 Often these infections do not respond to treatment until one has completely removed the infected hardware, furthering the idea that antibiotics alone are not the answer.10

What Can We Do In The OR To Reduce The Incidence Of Biofilm Contamination?
Ahlberg and colleagues stated that the most common cause of biomaterial-associated infection is through perioperative contamination.11 Ultimately, the development of an infection depends upon the interaction among the implant, the infecting organism and the host’s immune system.11

In the perioperative setting, prophylaxis through cleansing of the skin and administration of weight-dosed antibiotics are standard across operating rooms nationwide.5 Operating room sterility is a topic of contention. As much as we believe the environment we work so hard to create is free of contamination, the literature says otherwise as no operating room is truly sterile.

Regarding the back table, splash basins used to rinse instruments have a contamination rate from 2 to 74 percent while irrigation fluid in one study had a 62 percent positive culture rate.16 Despite these findings, no correlation exists between back table contamination and skin/skin structure infection. A study of patients undergoing a total knee arthroplasty (TKA) showed an operative field contamination rate of 63 percent with 76 percent of organisms being coagulase-negative Staphylococcus.16 During a surgical procedure of one hour or less, authors have reported that the total number of bacteria-laden particles that fall into the wound amounts to 270 bacteria/cm2, which one would assume to be greater in surgeries longer than one hour.6,16

One way the surgeon can reduce the potential for biofilm existence is through hardware alloy choice. Connaughton and colleagues noted that Staphylococcus spp. have a decreased adherence and biofilm layer creation on titanium versus stainless steel or PMMA.4 In a study of biofilm load on titanium versus stainless steel K-wires in toe surgery, infections and biofilm formation were reduced when surgeons used titanium.17

One usually treats deep infection in the presence of an implant with systemic antibiotic therapy; surgical removal of the implant (either a polyethylene spacer, metallic stem components or both); culturing of the soft tissue, surrounding bone, and implant itself; serial debridement of bone and soft tissue; and potential placement of antibiotic-PMMA spacers or coatings on hardware.6,12,15,18,19 The second-stage surgery often occurs once parameters like blood work markers have normalized, especially once the patient is off antibiotic therapy.12 Despite this being the standard of care, success rates are highly variable ranging from 18 to 100 percent in hip and knee revision surgeries.4,12,18,19 Revision surgeries and secondary implantation of prosthesis reportedly have a greater risk for infection than the primary implant.6

Authors have published antibiotic recommendations regarding the duration and type of antibiotic as well as the biomaterial infection situation.20 In patients with prosthesis retention, one should utilize a one-stage exchange surgery or a two-stage exchange surgery with a short interval between operations (two to four weeks) and three months of antibiotic therapy. This includes two to four weeks of IV antibiotics followed by oral antibiotics to finish the course. In the two-stage exchange surgery with a long interval (more than eight weeks), one would implement the same protocol with the exception of stopping antibiotic use two weeks prior to surgery in order to obtain reliable tissue cultures at the time of surgery. In fracture surgery, the treatment is three months with implant retention but only six weeks if one has removed all of the hardware. Trampuz and coworkers list specific antibiotic treatment protocols for implant-associated infections for further review.20

For local antibiotic delivery, one technique is the use of antibiotic-PMMA to increase the local concentration of antibiotic in the soft tissue and bone. The surgical approach consists of component exchange for antibiotic-PMMA spacers or coating the revision implant, which surgeons may do off-label. Surgeons often use tobramycin and vancomycin powders due to their broad spectrum coverage, heat stability, synergistic effect in combination, and elution characteristics.15 The antibiotic elutes in a biphasic fashion: the initial rapid phase (which peaks at approximately 18 hours) and the secondary phase, which occurs five to 10 days later.14,15,21

What Can We Do From An Implant Standpoint To Reduce Biofilm?
The design of the biomaterial can have a role in reducing infection rates. The greatest problem lies in the biomaterial implanted not being completely inert and biocompatible with the surrounding tissues. The implant-tissue interface induces a foreign-body type response, creating local inflammation and an area prone to infections, ending with lack of integration with the local tissues and implant failure.22
The contamination of a surface is the phenomenon known as “fouling.” Anti-fouling is the process of removing or preventing biofilm formation on a surface. This process has anti-infective benefits (primary resistance to infections) and delivers a medical therapy to prevent, treat or reduce infection.23

In the “race to the surface,” a biomaterial that allows host tissue integration over microbial adhesion would be ideal. Conversely, a surface that resists microbial attachment but favors host tissue adhesion would also be ideal. The problem with this is multifaceted. Many of the biomaterial surfaces that facilitate host cell adhesion are also adhesive to microorganisms. Alternatively, the use of techniques to resist microorganism attachment to biomaterial surfaces will also inhibit host cell integration.6 Some studies even suggest that the microbes attach to these anti-fouling surfaces and modify the surface to increase its microbe binding ability.2

Some of the characteristics employed by the manufacturer to decrease microbial surface adherence include creating hydrophilic, highly hydrated, anionic surfaces, non-charged surfaces, polyethylene oxide coatings, silicone coatings and heparin coatings.4,23 Researchers are currently looking at decreasing biofilm attachment through gene mutation of the pili and flagella, decreasing the motility and adherence capabilities of the microorganisms.9

Further examples of anti-fouling agents include special coatings of materials on the implants. Metals and ions with bioactive, innate antibacterial properties such as silver, copper, titanium and iron can be coated on the surface of implants to inhibit bacterial adhesion, or create ion release that disrupts essential bacterial growth processes.1,4 We do not yet fully understand this method and it has the risk of reaching higher than desired concentrations of ions, causing local tissue toxicity, local osteolysis and hardware failure, or accumulation in distant organs.23 Other bioactive biomaterial coatings include nitric oxide, zinc oxide, titanium oxide, calcium peroxide, reactive oxygen species and bioactive glass.23 The approach of antimicrobial coatings (antibiotic releasing) to biomaterial surfaces often fails in the in vitro testing phase due to either product design or the inability to convert testing to the in vivo phase due to trials needing to enroll too large a population, high costs and length of the study required.6

Newer technologies in this field have emerged. Physicians have implemented nanotechnologies and nanoparticles on biomaterials showing antibacterial activity.3,23 There have also been trials on the use of electrical stimulation and pulsed electromagnetic fields on implant surfaces.11 Studies have shown that the application of currents to stainless steel implants infected with S. aureus and S. epidermis was able to enhance detachment of the biofilm and reduce bacterial load.4 One could use this method in conjunction with systemic antibiotic therapy, reducing the removal and re-implantation surgery technique that clinicians currently employ.

Another technique is laser-generated shockwaves that involve the use of mechanical energy to break up biofilms. In one study, the use of laser removed 97.9 percent of P. aeruginosa biofilm on a nitinol surface.4 However, there needs to be more research on this line of therapy. One more strategy to prevent infection is through bacteriophagic viruses although in vivo studies are limited. Notable problems with phages are that they exhibit a narrow specificity against multiple species or strains of bacteria, and the bacteria’s ability to confer a resistance to the phage. Bacteria in biofilm form have a higher DNA replication mutation rate, assisting in this resistance.1

In spite of all the methods listed above, the progress in improving biomaterial surfaces has been limited. It is difficult to create a “perfect” implant that resists microbial adhesion on every surface or implement a strategy to block phenotypic changes and mutations toward the enhanced microbial adhesion, the extracellular polymeric substance protection layer and the speed in which resistance to antibiotics occurs.

In Conclusion
It is evident that the science of biomaterial implantation and the prevention of infection are not foolproof. There is a necessity for improvement in the process of long-term integration of biomaterials and tissue, which may reduce the number of infections. The implantation of biomaterials in the human body is a $300 billion industry worldwide. They often save lives and improve the quality of life for millions of people.24 Complications do happen but as surgeons, we can do our part to not only lower the risk but act in an evidence-based way to treat the problem.

If biofilms have taught us anything about infection, it is that relying solely on antibiotics is not enough. The current treatment methods are becoming less effective as resistance and virulence increases faster than industry can produce new antibiotic therapies. Various new technologies are in the works to help advance biofilm disruption. However, the tried and true concept of improving the biocompatibility of the material appears to be the most important in the “race for the surface.” As healthcare professionals, we need to gain the upper hand in terms of biofilm eradication, especially biofilms pertaining to implant contamination. n

Dr. Cornell is in private practice at the Foot Care Center in Havertown, Pa. She is also an attending physician with the Crozer Keystone Health System Residency Training Program.

Dr. Hood is the Chief Resident in the Department of Foot and Ankle Surgery with the Crozer Keystone Health System in Upland, Pa.


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Additional References

    25. Myerson MS, Shariff R, Zonno AJ. The management of infection following total ankle replacement: demographics and treatment. Foot Ankle Int. 2014; 35(9):855-862.
    26. Fernandes A, Dias M. The microbiological profiles of infected prosthetic implants with an emphasis on the organisms which form biofilms. J Clin Diagn Res. 2013;7(2):219-223.

Editor’s note: For further reading, see “Can Ultrasound Debridement Facilitate Biofilm Removal From Diabetic Foot Ulcers?” in the August 2014 issue.

Rhonda S. Cornell, DPM, and Christopher R. Hood, Jr., DPM
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