Infections Associated with Prosthetic Devices: Magnitude of the Problem

Freezing nitrogen ethanol composite reduces periprosthetic infection caused by Staphylococcus aureus contaminated metal implants: An animal study

BACKGROUND

Implant-associated infection remains a major complication of orthopedic surgery. The treatment of such infection is complicated by bacterial biofilm formation on the metal surfaces of implants. Biofilm surrounds and protects the bacteria against the organism's endogenous defense system and from external agents such as antibiotics and mechanical debridement. This study aims to evaluate whether freezing nitrogen ethanol composite (FNEC), the combination of liquid nitrogen and 95% ethanol in a 3 to 1 ratio, used frequently in bone tumor surgery, is capable of disinfecting Staphylococcus aureus contaminated implants.

METHODS

The femurs of six New Zealand white rabbits were implanted with S. aureus-contaminated screws, half of which were treated with FNEC before implantation. The femurs were harvested 14 days after implantation. Histological analysis and TUNEL assay were conducted. The autoclaved screw, contaminated screw, and FNEC-treated contaminated screw were investigated using scanning electron microscopy to evaluate the biofilm structure.

RESULTS

The FNEC-treated group had significantly lower relative C-reactive protein levels. An obvious periosteal reaction at the implant site was observed in all rabbits in the non-FNEC group but none was observed in the FNEC-treated group. The FNEC-treated group exhibited fewer empty lacunae, less inflammatory infiltration, and less bone necrosis. Immunohistochemical analysis showed no S. aureus in bone tissue from the FNEC-treated group. Scanning electron microscopy showed disruption of the biofilm on the contaminated screw treated with FNEC.

CONCLUSION

FNEC showed potential in disinfecting S.aureus-contaminated implants. Further investigation is warranted, such as the effect on the implant-cement-bone interface, for FNEC to be used clinically in treating implant-associated infection.

The Effect of Peritoneal Dialysis Solutions on Rifampin Action againstStaphylococcus Epidermidisin the Fluid and Biofilm Phases of Growth

Continuous ambulatory peritoneal dialysis (CAPD) catheter-assoclated infections can be resistant to conservative therapeutic measures despite the apparent susceptibility of the infecting bacterial strains to antibiotics. This chronicity of Infection has been ascribed to the development of bacteria on the surfaces of catheter material within a protective polysaccharide shield or matrix. CAPD catheters are unique In being exposed to nonphysiological environments of dialysis fluids of varying physical properties and constitution. We determined that the rate of growth of s. epidermldis In the fluid phase In laboratory media or fresh dialysis solution was significantly Influenced by pH. An acid milieu (pH 5) Impaired growth compared to a neutral milieu (pH 7). Spent dialysis fluid, however, which had an approximately neutral pH, also Impaired bacterial growth, the assumption being that this results from properties of spent fluid unrelated to pH.

Using rifampin as the test antibiotic, we noted that Its action on S. epidermldis was unaffected by pH or by the differing milieu of fresh and spent fluid. Bacterial growth was arrested regardless of the milieu. We further examined the potential of dialysis fluids to modify the Interaction between rifampin and the matrix-enclosed bacteria of standardized S. epidermidis blofilms. We determined that the pH of the dialysis solution was a critical factor Influencing the outcome of exposure of the biofilm to rifampin. An acid pH enhanced antibiotic activity, whereas a neutral pH was associated with antibiotic antagonism. These findings have Implications in the management of S. epidermldis catheter-associated infections using rifampin. Administration of the antibiotic In fresh peritoneal dialysis solution (pH 5.6) Is Judged more likely to be associated with a successful outcome.

Infections Associated with Prosthetic Devices: Clinical Considerations

The successful development of synthetic materials and introduction of artificial devices into nearly all body systems has been shadowed by the adaptation of microorganisms to the opportunities these devices afford for eluding defenses and invading the host. Clinicians are faced with the task of recognizing the manifestations of device-associated infection, predicting the likely pathogens involved, knowing the appropriate diagnostic methods, and initiating appropriate therapy. Infections associated with prosthetic heart valves are particularly challenging to successfully treat; surgical replacement may be necessary. Infection associated with an artificial joint usually requires removal of the device in addition to appropriate antibiotics. Intravascular associated infections are the leading cause of nosocomial bacteremias and, because of their intravascular location, these infections are often life catheter threatening if not promptly diagnosed and treated. Even contact lenses, external to epithelial surfaces, may give rise to serious sight-threatening infections. Although artificial devices play a paramount role in medicine today, infection is an ever present potential with which clinicians must be familiar.

In Vivo Assessment of Phage and Linezolid Based Implant Coatings for Treatment of Methicillin Resistant S. aureus (MRSA) Mediated Orthopaedic Device Related Infections

Staphylococcus comprises up to two-thirds of all pathogens in orthopaedic implant infections with two species respectively Staphylococcus aureus and Staphylococcus epidermidis, being the predominate etiological agents isolated. Further, with the emergence of methicillin-resistant S. aureus (MRSA), treatment of S. aureus implant infections has become more difficult, thus representing a devastating complication. Use of local delivery system consisting of S.aureus specific phage along with linezolid (incorporated in biopolymer) allowing gradual release of the two agents at the implant site represents a new, still unexplored treatment option (against orthopaedic implant infections) that has been studied in an animal model of prosthetic joint infection. Naked wire, hydroxypropyl methylcellulose (HPMC) coated wire and phage and /or linezolid coated K-wire were surgically implanted into the intra-medullary canal of mouse femur bone of respective groups followed by inoculation of S.aureus ATCC 43300(MRSA). Mice implanted with K-wire coated with both the agents i.e phage as well as linezolid (dual coated wires) showed maximum reduction in bacterial adherence, associated inflammation of the joint as well as faster resumption of locomotion and motor function of the limb. Also, all the coating treatments showed no emergence of resistant mutants. Use of dual coated implants incorporating lytic phage (capable of self-multiplication) as well as linezolid presents an attractive and aggressive early approach in preventing as well as treating implant associated infections caused by methicillin resistant S. aureus strains as assessed in a murine model of experimental joint infection.

Orthopaedic device-related infection: current and future interventions for improved prevention and treatment

Orthopaedic and trauma device-related infection (ODRI) remains one of the major complications in modern trauma and orthopaedic surgery.Despite best practice in medical and surgical management, neither prophylaxis nor treatment of ODRI is effective in all cases, leading to infections that negatively impact clinical outcome and significantly increase healthcare expenditure.The following review summarises the microbiological profile of modern ODRI, the impact antibiotic resistance has on treatment outcomes, and some of the principles and weaknesses of the current systemic and local antibiotic delivery strategies.The emerging novel strategies aimed at preventing or treating ODRI will be reviewed. Particular attention will be paid to the potential for clinical impact in the coming decades, when such interventions are likely to be critically important.The review focuses on this problem from an interdisciplinary perspective, including basic science innovations and best practice in infectious disease. Cite this article: Moriarty TF, Kuehl R, Coenye T, et al. Orthopaedic device related infection: current and future interventions for improved prevention and treatment. EFORT Open Rev 2016;1:89-99. DOI: 10.1302/2058-5241.1.000037.

A doxycycline-loaded polymer-lipid encapsulation matrix coating for the prevention of implant-related osteomyelitis due to doxycycline-resistant methicillin-resistant Staphylococcus aureus

Implant-associated bone infections caused by antibiotic-resistant pathogens pose significant clinical challenges to treating physicians. Prophylactic strategies that act against resistant organisms, such as methicillin-resistant Staphylococcus aureus (MRSA), are urgently required. In the present study, we investigated the efficacy of a biodegradable Polymer-Lipid Encapsulation MatriX (PLEX) loaded with the antibiotic doxycycline as a local prophylactic strategy against implant-associated osteomyelitis. Activity was tested against both a doxycycline-susceptible (doxy(S)) methicillin-susceptible S. aureus (MSSA) as well as a doxycycline-resistant (doxy(R)) methicillin-resistant S. aureus (MRSA). In vitro elution studies revealed that 25% of the doxycycline was released from the PLEX-coated implants within the first day, followed by a 3% release per day up to day 28. The released doxycycline was highly effective against doxy(S) MSSA for at least 14days in vitro. A bolus injection of doxycycline mimicking a one day release from the PLEX-coating reduced, but did not eliminate, mouse subcutaneous implant-associated infection (doxy(S) MSSA). In a rabbit intramedullary nail-related infection model, all rabbits receiving a PLEX-doxycycline-coated nail were culture negative in the doxy(S) MSSA-group and the surrounding bone displayed a normal physiological appearance in both histological sections and radiographs. In the doxy(R) MRSA inoculated rabbits, a statistically significant reduction in the number of culture-positive samples was observed for the PLEX-doxycycline-coated group when compared to the animals that had received an uncoated nail, although the reduction in bacterial burden did not reach statistical significance. In conclusion, the PLEX-doxycycline coating on titanium alloy implants provided complete protection against implant-associated MSSA osteomyelitis, and resulted in a significant reduction in the number of culture positive samples when challenged with a doxycycline-resistant MRSA.

Local delivery of linezolid from poly-D,L-lactide (PDLLA)-linezolid-coated orthopaedic implants to prevent MRSA mediated post-arthroplasty infections

The present study focuses on the use of linezolid as local delivery agent for direct administration of the drug at the orthopaedic implant site. Local drug delivery system with linezolid added to the Poly D, L-(Lactide) polymer solution was used to coat the orthopaedic grade K-wires. Bacterial adherence on K-wires was then determined to evaluate the effect of the coated drug on the adherence of MRSA. A significant decrease in bacterial adherence as compared to naked wires was observed on all the coated K-wires (2.5, 5 and 10% w/w linezolid coated) with maximum decrease of 60%. This represents an aggressive early approach to prevent initial adherence of bacterial population. With the rise in MRSA mediated orthopaedic device related infections, the use of linezolid loaded polymer coated implants is definitely an attractive strategy against drug resistant strains of S. aureus.

An overview of the methodological approach to the in vitro study of anti-infective biomaterials

Biomaterial-associated infections have an enormous impact in terms of morbidity of the patients and costs to national health systems. Perioperative antibiotics and aseptic procedures have not proved sufficient to eradicate the occurrence of this type of infections which often lead to devastating effects. Adjunctive strategies for preventing the establishment of infections are increasingly being centered on the development of new biomaterials with anti-infective properties. The creation of new anti-infective biomaterials can be obtained by alternative approaches oriented to achieve either bacteria-repellent surfaces or bioactive surfaces expressing self-sterilizing properties when not even able to treat pre-existing infections in the surrounding tissues. Here, we offer a short overview of the currently available in vitro methods that can be used to investigate and assess the performance of anti-infective biomaterials, with special emphasis on those whose mechanism of action is based on bacteria-repellent surfaces.

Bactericidal property and biocompatibility of gentamicin-loaded mesoporous carbonated hydroxyapatite microspheres

Implant-associated infection is a serious problem in orthopaedic surgery. One of the most effective ways is to introduce a controlled antibiotics delivery system into the bone filling materials, achieving sustained release of antibiotics in the local sites of bone defects. In the present work, mesoporous carbonated hydroxyapatite microspheres (MCHMs) loaded with gentamicin have been fabricated according to the following stages: (i) the preparation of the MCHMs by hydrothermal method using calcium carbonate microspheres as sacrificial templates, and (ii) loading gentamicin into the MCHMs. The MCHMs exhibit the 3D hierarchical nanostructures constructed by nanoplates as building blocks with mesopores and macropores, which make them have the higher drug loading efficiency of 70-75% than the conventional hydroxyapatite particles (HAPs) of 20-25%. The gentamicin-loaded MCHMs display the sustained drug release property, and the controlled release of gentamicin can minimize significantly bacterial adhesion and prevent biofilm formation against S. epidermidis. The biocompatibility tests by using human bone marrow stromal cells (hBMSCs) as cell models indicate that the gentamicin-loaded MCHMs have as excellent biocompatibility as the HAPs, and the dose of the released gentamicin from the MCHMs has no toxic effects on the hBMSCs. Hence, the gentamicin-loaded MCHMs can be served as a simple, non-toxic and controlled drug delivery system to treat bone infections.

Emerging ideas: Interleukin-12 nanocoatings prevent open fracture-associated infections

BACKGROUND

Infection is a major clinical complication of orthopaedic implants and prosthetic devices, and patients with traumatic open fractures have a high risk of infection that may exceed 30%. Surgical trauma, burns, and major injuries such as traumatic open fractures induce immunosuppression, decrease resistance to infection, and decrease production of T helper type 1 (Th1) cytokines.

QUESTIONS/HYPOTHESES

Exogenous interleukin-12 p70 (IL-12p70 or IL-12), a natural cytokine that plays a central role in Th1 response and bridges innate and adaptive immunities, will reduce open fracture-associated infection.

METHOD OF STUDY

We propose using exogenous IL-12 nanocoating to restore or enhance the body's natural defense system to combat pathogens. Rats will have a femur fractured, inoculated with Staphylococcus aureus or injected with phosphate buffered saline, left open for 1 hour, and then fixed with an intramedullary Kirschner wire with or without IL-12 nanocoating. Animals will be euthanized at postoperative Day 21; samples of blood, soft tissue, bone, and draining lymph nodes will be collected. Infection, bone healing, and local and systemic responses will be determined.

SIGNIFICANCE

IL-12 nanocoating is a promising prophylactic means to modulate the host immune response to help prevent open fracture-associated infections and to avoid the problem of antibiotic resistance.

Efficacy of moxifloxacin compared to teicoplanin in the treatment of implant-related chronic osteomyelitis in rats

Treatment of implant-related chronic osteomyelitis is often difficult and usually consists of implant removal, extensive surgical debridement, and prolonged antibiotic use. This study was performed to assess the efficacy of moxifloxacin compared to a glycopeptide, teicoplanin in chronic implant-related methicillin-sensitive Staphylococcus aureus (MSSA) osteomyelitis. The left femoral medullar cavities of 60 Wistar male rats were contaminated with 100 µl of 10(8) cfu/ml methicillin-sensitive S. aureus (ATCC 29213) and Kirschner wires were placed into the medulla of the femur. After 6 weeks, rats were randomly divided into five groups. In two groups, the Kirschner wires were removed. Experimental groups were as follows: group 1: contaminated, Kirschner wire inside, received teicoplanin; group 2: contaminated, Kirschner wire removed, received teicoplanin; group 3: contaminated, Kirschner wire inside, received moxifloxacin; group 4: contaminated, Kirschner wire removed, received moxifloxacin; group 5: contaminated, Kirschner wire inside, no antibiotics (control group). Groups 1 and 2 received teicoplanin (20 mg/kg once daily), whereas groups 3 and 4 received moxifloxacin (10 mg/kg twice daily) intraperitoneally for 28 days. At the end of the treatment, animals were sacrificed by inhalation anesthesia with ether and femora were retrieved and bacterial counts (cfu/g) were determined. Bacterial counts in all study groups were significantly reduced relative to the control. The decrease of bacterial counts was more prominent in group 4 compared to group 1 (p = 0.001) and group 2 (p = 0.003). Moxifloxacin therapy is an effective alternative to teicoplanin for chronic implant-related MSSA osteomyelitis.

Polypeptide nanocoatings for preventing dental and orthopaedic device-associated infection: pH-induced antibiotic capture, release, and antibiotic efficacy

Implant-associated infection is one of the most common and problematic complications for dental and orthopaedic patients. Modification of currently used implant surfaces aimed at bestowing them with antibacterial properties is a promising approach in the development of new biomaterials. In this study, a novel nanotechnology, that is, electrostatic self-assembly, was developed to construct biomimetic polypeptide nanocoatings on commonly used metal implants. A model antibacterial drug, cefazolin, was captured in the polypeptide nanocoating and its release was studied. We have shown that the capture and release of cefazolin was pH-induced and could be controlled, and the developed antibiotic-incorporated polypeptide multilayer nanocoatings could prevent Staphylococcus aureus colonization thus showing great potential for preventing implant-associated infection.

Synthesis and characterization of Ag/Cu/HAP with platelet morphology

As a useful starting material in coating technology and preparation of HAP/polymers composites the platelet Ag/Cu/HAP was prepared using the solid solution of HAP reacting with the mix-solution of silver and copper nitrate. Its composition, microstructure and properties were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and anti-bacterial or bacteriostatic tests. The results demonstrate that the prepared Ag/Cu/HAP crystal is mainly comprised of HAP phase with little whitelockite and silver phosphate, stable up to 600 degrees C and takes a platelet shape. At 750 degrees C, it is partially changed into whitelockite, calcium copper phosphate, silver oxide and silver phosphate. The platelet Ag/Cu/HAP crystal has a preferential orientation of a-axis below 600 degrees C, above which the growth in a-axis is greatly inhibited. The Ag/Cu/HAP has good crystallinity at 600 degrees C and is the most effective powder in resisting bacteria among the HAP powders investigated. The platelet Ag/Cu/HAP crystal can be good starting materials to make antibacterial polymers/HAP composites and HAP coatings.

S. epidermidis biofilm formation: effects of biomaterial surface chemistry and serum proteins

Most infections due to implanted cardiovascular biomaterials are initiated by bacterial adhesion of Staphylococcus epidermidis, followed by colonization and biofilm formation on the surface of the implant. This study examined the role of serum proteins and material surface chemistry in the formation of S. epidermidis biofilm on polyurethanes (Elasthane 80A, hydrophobic) modified with polyethylene oxide (Elasthane 80A-6PEO, hydrophilic) and fluorocarbon (Elasthane 80A-6F, hydrophobic). Initial adhesion, aggregation, biofilm thickness, viability, and slime formation of S. epidermidis strain, RP62A in phosphate buffered saline (PBS), tryptic soy broth (TBS), and 20% pooled human serum was quantified. In the presence of adsorbed serum proteins, initial bacterial adhesion was suppressed significantly to <2% relative to adhesion in TSB or PBS. However, adhesion, aggregation, and proliferation increased dramatically in the 12-24 h period on Elasthane 80A and Elasthane 80A-6F, which resulted in an extensive network of biofilm. A contrasting trend was observed on the hydrophilic Elasthane 80A-6PEO surface, with minimal bacterial adhesion, which decreased steadily over 24 h. In the presence of serum proteins, an increasingly thick ( approximately 20 mum) biofilm formed on the hydrophobic surfaces over 48 h whereas the formation of a mature biofilm on the hydrophilic surface was impeded with few viable bacteria present over 48 h. Furthermore, slime was detected during the initial phase of bacterial adhesion at 2 h and increased over time with the formation of biofilm. These results have shown that while initial S. epidermidis adhesion is suppressed in the presence of adsorbed proteins, inter-bacterial adhesion possibly aided by slime production leads to the formation of a robust mature biofilm. Also, biomaterial surface chemistry affected biofilm formation and, most notably, polyethylene oxide significantly inhibited S. epidermidis biofilm formation over 48 h in vitro.

iNOS-mediated generation of reactive oxygen and nitrogen species by biomaterial-adherent neutrophils

Infection due to implanted cardiovascular biomaterials is a serious complication initiated by bacterial adhesion to the surface of the implant. The release of reactive oxygen species by neutrophils, particularly superoxide anion, is a well-known bactericidal mechanism. Additionally, nitric oxide (NO) has also been identified as an important cytotoxic mediator in acute and chronic inflammatory responses with enhanced NO production by upregulation of inducible nitric oxide synthase (iNOS). The interaction of NO and superoxide anion will result in the formation of peroxynitrite (OONO-), a potent cytotoxic oxidant. In this study, we have shown that biomaterial-induced neutrophil activation does not cause upregulation of iNOS and activation of iNOS-mediated pathways. However, NO and O2- production does occur over time upon adhesion to a biomaterial and is modulated by biomaterial surface chemistry. With no stimulus, the polyethylene oxide-modified polyurethane induced greater neutrophil activation than did the control as indicated by the increased production of NO and O2- over time. Adherent-stimulated neutrophils generally produced lower amounts of NO over time in comparison with unstimulated cells. Furthermore, there is no evidence of peroxynitrite activity in unstimulated neutrophils adherent to the Elasthane 80A. However, upon stimulation with adherent Staphylococcus epidermidis, peroxynitrite formation did occur. Our results suggest that bactericidal mechanisms in neutrophils involving NO generation (NOS pathway) are further compromised than O2- producing pathways (NADPH oxidase) upon exposure to biomaterials, resulting in a diminished microbial killing capacity, which can increase the probability of device-centered infections.

Effect on infection resistance of a local antiseptic and antibiotic coating on osteosynthesis implants: an in vitro and in vivo study

The purpose of this study was to acquire information about the effect of an antibacterial and biodegradable poly-L-lactide (PLLA) coated titanium plate osteosynthesis on local infection resistance. For our in vitro and in vivo experiments, we used six-hole AO DC minifragment titanium plates. The implants were coated with biodegradable, semiamorphous PLLA (coating about 30 microm thick). This acted as a carrier substance to which either antibiotics or antiseptics were added. The antibiotic we applied was a combination of Rifampicin and fusidic acid; the antiseptic was a combination of Octenidin and Irgasan. This produced the following groups: Group I: six-hole AO DC minifragment titanium plate without PLLA; Group II: six-hole AO DC minifragment titanium plate with PLLA without antibiotics/antiseptics; Group III: six-hole AO DC minifragment titanium plate with PLLA + 3% Rifampicin and 7% fusidic acid; Group IV: six-hole AO DC minifragment titanium plate with PLLA + 2% Octenidin and 8% Irgasan. In vitro, we investigated the degradation and the release of the PLLA coating over a period of 6 weeks, the bactericidal efficacy of antibiotics/antiseptics after their release from the coating and the bacterial adhesion of Staphylococcus aureus to the implants. In vivo, we compared the infection rates in white New Zealand rabbits after titanium plate osteosynthesis of the tibia with or without antibacterial coating after local percutaneous bacterial inoculations at different concentrations (2 x 10(5)-2 x 10(8)): The plate, the contaminated soft tissues and the underlying bone were removed under sterile conditions after 28 days and quantitatively evaluated for bacterial growth. A stepwise experimental design with an "up-and-down" dosage technique was used to adjust the bacterial challenge in the area of the ID50 (50% infection dose). Statistical evaluation of the differences between the infection rates of both groups was performed using the two-sided Fisher exact test (p < 0.05). Over a period of 6 weeks, a continuous degradation of the PLLA coating of 13%, on average, was seen in vitro in 0.9% NaCl solution. The elution tests on titanium implants with antibiotic or antiseptic coatings produced average release values of 60% of the incorporated antibiotic or 62% of the incorporated antiseptic within the first 60 min. This was followed by a much slower, but nevertheless continuous, release of the incorporated antibiotic and antiseptic over days and weeks. At the end of the test period of 42 days, 20% of the incorporated antibiotic and 15% of the incorporated antiseptic had not yet been released from the coating. The antibacterial effect of the antibiotic/antiseptic is not lost by integrating it into the PLLA coating. The overall infection rate in the in vivo investigation was 50%. For Groups I and II the infection rate was both 83% (10 of 12 animals). In Groups III and IV with antibacterial coating, the infection rate was both 17% (2 of 12 animals). The ID50 in the antibacterial coated Groups III and IV was recorded as 1 x 10(8) CFU, whereas the ID50 values in the Groups I and II without antibacterial coating were a hundred times lower at 1 x 10(6) CFU, respectively. The difference between the groups with and without antibacterial coating was statistically significant (p = 0.033). Using an antibacterial biodegradable PLLA coating on titanium plates, a significant reduction of infection rate in an in vitro and in vivo investigation could be demonstrated. For the first time, to our knowledge, we were able to show, under standardized and reproducible conditions, that an antiseptic coating leads to the same reduction in infection rate as an antibiotic coating. Taking the problem of antibiotic-induced bacterial resistance into consideration, we thus regard the antiseptic coating, which shows the same level of effectiveness, as advantageous.

Prophylaxis and treatment of implant-related infections by antibiotic-coated implants: a review

Implant-related infection is a feared complication in orthopedic and trauma surgery with tremendous consequences for the patient. To reduce this risk, administration of perioperative antibiotic prophylaxis is a routine procedure in orthopedic surgery. A local delivery system for antibiotics based on a polymer implant coating has been developed to optimize the prophylaxis. In an animal experiment, the efficacy of local prophylaxis of gentamicin was compared to a systemic single shot of gentamicin and to a combination of both administrations. The medullary cavities of rat tibiae were contaminated with Staphylococcus aureus and titanium K-wires were implanted into the medullary canals. For local antibiotic therapy, the implants were coated with poly(D,L-Lactide) (PDLLA) loaded with gentamicin. All the animals not treated with local and systemic application of the antibiotic developed osteomyelitis and all cultures of the implants tested positive for S. aureus. Onset of infection was prevented in 80-90% of animals treated with gentamicin-coated K-wires, with and without systemic prophylaxis. Gentamicin-coated intramedullary tibial nails are CE-certified for Europe and Canada and several patients have already been treated for implant-related infection. Up to now, eight patients with open tibia fractures have been treated with an unreamed tibial nail (UTN) coated with PDLLA and gentamicin. In the 1-year follow up, none of the patients developed an infection. A prospective randomized clinical documentation is currently in progress. So far, the results suggest that a local application of gentamicin from PDLLA-coated implants might support systemic antibiotic prophylaxis in preventing implant-associated osteomyelitis.

In vivo biostability of polyether polyurethanes with polyethylene oxide surface-modifying end groups; resistance to biologic oxidation and stress cracking

Polyethylene oxide (PEO) on polymer surfaces has been reported to reduce cellular adhesion, a very desirable property for cardiac pacing leads. A Shore 80A polyether polyurethane with up to 6% PEO surface-modifying end groups (SME) was evaluated for its chronic in vivo biostability. In a short-term (12 week) screening test, strained samples appeared to develop the same surface oxidation as unmodified polymer, but did not produce visible cracking > or =500x, prompting a longer-term study. By the time the longer-term study was initiated, most of the PEO SME had disappeared from the starting material's surface. After 1 year in vivo, surface oxidation, shallow surface cracking, and environmental stress cracking (ESC) developed on highly strained samples to the point of failure, so that there was no significant difference between the SME polymer and its control (the same polymer without SME). No further change was seen for up to 2 years of implantation. Unstrained PEO SME polymer developed shallow surface cracking, but no ESC up to 2 years of implantation. Thus, PEO SME slightly delayed, but did not stop biodegradation, and under unstrained conditions, has no adverse effect on biostability.

Phospholipid polymer surfaces reduce bacteria and leukocyte adhesion under dynamic flow conditions

Persistence of infection can occur when the host immune response is compromised because of the presence of a foreign implant. Surface modification of biomaterials with phospholipid polymers may enhance biocompatibility and reduce incidence of infection by impeding bacterial and leukocyte adhesion. A rotating disk model, which generates shear stress from 0 to 18 dynes/cm(2), was used to characterize adhesion of neutrophils, monocytes, and bacteria in phosphate-buffered saline (PBS) or 25% human serum on polyethylene terephthalate surfaces coated with a phospholipid polymer, poly[omega-methacryloyloxyalkyl phosphorylcholine (MAPC)-co-n-butyl methacrylate (BMA)]. The material designated PMB30 contains a methylene chain length, (CH(2))(n), of n = 2, whereas PMHB30 contains a chain length of n = 6. In PBS, bacterial adhesion was shear stress dependent with the lowest bacterial density observed on PMB30. However, the presence of serum proteins eliminated shear stress and surface chemistry effects in addition to bacterial adhesion reduced to <10% of adhesion in PBS. Trends for leukocyte adhesion in serum demonstrated shear dependence with PMB30 exhibiting the lowest cell density throughout the range of shear stresses. In conclusion, modification of the polyethylene terephthalate surfaces with phospholipid polymers resulted in reduced bacterial and leukocyte adhesion. Furthermore, shortening the methylene chain length of the MAPC copolymer most effectively reduced adhesion.

Development of an infection-resistant, bioactive wound dressing surface

Trauma, whether caused by an accident or in an intentional manner, results in significant morbidity and mortality. The goal of this study was to develop a novel biomaterial surface in vitro and ex vivo that provides both localized infection resistance nd hemostatic properties. Our hypothesis is that a combination of specific surface characteristics can be successfully incorporated into a single biomaterial. Functional groups were created with woven Dacron (Cntrl) material via exposure to ethylenediamine (C-EDA). The antibiotic ciprofloxacin (Cipro) was then applied to the C-EDA material using pad/autoclave technique (C-EDA-AB) followed by surface immobilization of the coagulation cascade enzyme thrombin (C-EDA-AB-Thrombin). Antimicrobial activity by the C-EDA-AB surface persisted for 5 days compared with Cntrl and dipped controls, which lasted <1 h. C-EDA-AB-Thrombin surfaces had 2.6- and 105-fold greater surface thrombin activity compared with nonspecifically bound thrombin and Cipro-dyed surfaces, respectively. Surface thrombus formation ex vivo was evident after 1 min of exposure, with thrombus organization evident by 2.5 min. In contrast, C-EDA-AB and Cntrl segments showed only blood protein adsorption on the fibers. Thus, this study demonstrated that Cipro and thrombin can be simultaneously incorporated onto a biomaterial surface while maintaining their respective biological activities.

Antibiotics on urethral catheter withdrawal: a hit and miss affair

Globally, millions of patients undergo urethral catheterization every year. Our objective was to study the current use of prophylactic antibiotics on urinary catheter withdrawal. A questionnaire (N = 300) was sent to healthcare professionals involved in the management of patients with urinary catheters (consultant microbiologists, infection control nurses, consultant urologists, specialist nurses in urology, continence advisers and consultants in the care of older people). The questionnaire asked about their use of prophylactic antibiotics on the withdrawal of a urethral catheter. Sixty percent of healthcare professionals advocated the use of antibiotics for either all or selected groups of patients. The remainder did not. The use of prophylactic antibiotics varied among different groups. Of the healthcare professionals who used antibiotics, the majority cited more than one reason for their use (prevent bacteraemia, avoid an infection in a prosthesis or urinary tract infection). The course and type of antibiotic used varied. Our study has shown diversity in practice that is of concern. At present, just over one-half of patients with urinary catheters are being given antibiotics, although there is no evidence to suggest that such an intervention confers any benefit. If benefits do not exist, these patients are being exposed to the harm of antibiotics and providers are incurring costs unnecessarily. A formal trial to address this issue is urgently needed.

Bacteriostatic properties of biomatrices against common orthopaedic pathogens

Tissue-engineered grafts for tissue regeneration include either mature or progenitor cells seeded onto biomatrices that provide shape and support for developing tissue. Popular biomaterials used in orthopaedic surgery include collagen type I, hyaluronic acid, hydroxyapatite, and polylactic polyglycolic acid (PLGA). Biomatrices with bacteriostatic properties may be beneficial in promoting tissue-engineered graft survival in patients susceptible to infection. We evaluated the bacteriostatic effects of these biomaterials on the growth of the four most common orthopaedic bacterial pathogens: Staphylococcus aureus, Staphylococcus epidermidis, beta-hemolytic Streptococcus, and Pseudomonas aeruginosa. Hyaluronic acid demonstrated the largest bacteriostatic effect on these pathogens by inhibiting bacterial growth by an average of 76.8% (p = 0.0005). Hydroxyapatite and collagen inhibited growth on average by 49.7% (p = 0.011) and 37.5% (p = 0.102), respectively. PLGA exhibited the least bacteriostasis with an average inhibition of 9.8% (NS) and actually accelerated the growth of beta-hemolytic Streptococcus and P. aeruginosa.

Inhibition of bacterial and leukocyte adhesion under shear stress conditions by material surface chemistry

Biomaterial-centered infections, initiated by bacterial adhesion, persist due to a compromised host immune response. Altering implant materials with surface modifying endgroups (SMEs) may enhance their biocompatibility by reducing bacterial and inflammatory cell adhesion. A rotating disc model, which generates shear stress within physiological ranges, was used to characterize adhesion of leukocytes and Staphylococcus epidermidis on polycarbonate-urethanes and polyetherurethanes modified with SMEs (polyethylene oxide, fluorocarbon and dimethylsiloxane) under dynamic flow conditions. Bacterial adhesion in the absence of serum was found to be mediated by shear stress and surface chemistry, with reduced adhesion exhibited on materials modified with polydimethylsiloxane and polyethylene oxide SMEs. In contrast, bacterial adhesion was enhanced on materials modified with fluorocarbon SMEs. In the presence of serum, bacterial adhesion was primarily neither material nor shear dependent. However, bacterial adhesion in serum was significantly reduced to < or = 10% compared to adhesion in serum-free media. Leukocyte adhesion in serum exhibited a shear dependency with increased adhesion occurring in regions exposed to lower shear-stress levels of < or = 7 dyne/cm2. Additionally, polydimethylsiloxane and polyethylene oxide SMEs reduced leukocyte adhesion on polyether-urethanes. In conclusion, these results suggest that surface chemistry and shear stress can mediate bacterial and cellular adhesion. Furthermore, materials modified with polyethylene oxide SMEs are capable of inhibiting bacterial adhesion, consequently minimizing the probability of biomaterial-centered infections.

A new model of implant-related osteomyelitis in rats

Infection related to osteosynthesis often has dramatic consequences for the patient. Prolonged hospitalization with systemic antibiotic therapy, several revision procedures, possible amputation, and even death may occur. To investigate the pathology of infection in orthopedic surgery, a new rat model of implant related osteomyelitis was developed. Three different concentrations (10(6), 10(3), and 10(2) colony-forming units (CFU)/10 microl) of Staphylococcus aureus were inoculated into the tibial medullary cavity with simultaneous insertion of a titanium Kirschner wire. Controls received phosphate-buffered saline (PBS). Each group consisted of 10 animals. Animals were followed for 4 weeks until sacrifice. X-rays of the tibiae were taken weekly, blood counts were analyzed, and body temperature and weight were determined. After sacrifice, infection was evaluated by histological and microbiological investigations. All animals inoculated with Staph. aureus in either concentration developed microbiological, histological, and radiological signs of osteomyelitis in correlation to the amount of inoculated bacteria. X-rays clearly revealed osseous destruction after 14 days with progression of osteomyelitis during the following weeks. CFU/g bone and bone weight after sacrifice showed dependence on the amount of inoculated CFU. The histological results confirmed the radiological findings. No significant changes in blood counts, body weight, and body temperature between the groups could be observed. The results demonstrate that it is possible to develop a model of implant-related osteomyelitis in rats with dependence on the amount of inoculated bacteria. No other promoters of infection besides intramedullary insertion of titanium Kirschner wires were used in this model.

Antibiotic prophylaxis for patients with joint prostheses - still a dilemma for dental practitioners

OBJECTIVES

To provide a critical review of the current evidence that implicates dental-induced bacteraemia as a risk for joint infections in patients fitted with joint prostheses and appraise the need for antibiotic prophylaxis.

DESIGN

Retrospective analysis.

SETTING

Mainly hospital-based patients or subjects.

OUTCOME MEASURES

The relationship between joint infections and dental treatment is equivocal at the best and there is no evidence that antibiotic prophylaxis provides such patients with any protection.

RESULTS

Microbiological evidence linking dental treatment-induced bacteraemia to joint infections is weak and if an oral commensal is implicated, it is more likely to have arisen either from a spontaneous bacteraemia or from a dental infection. As a consequence of the latter, we recommended the institution of good dental health prior to joint replacement. There may be a case for providing prophylaxis to the immuno-compromised patient, but only if the immuno-suppression is associated with a neutropenia. In such circumstances, only emergency treatment should be considered until the neutropenia is resolved. Antibiotic regimens that are recommended by orthopaedic surgeons have not been evaluated in a randomised placebo-controlled study and many of the drugs are not licensed for this purpose. The evidence on cost-risk benefit seems to demonstrate that antibiotic prophylaxis with either amoxicillin or penicillin is not cost effective when compared with no prophylaxis.

CONCLUSION

The case for providing antibiotic prophylaxis prior to dental treatment in patients fitted with a joint prosthesis is weak or virtually non-existent. Furthermore, the risk from providing prophylaxis is greater than the risk of a joint infection.

Gentamicin coating of metallic implants reduces implant-related osteomyelitis in rats

Antibiotic prophylaxis is a routine procedure in orthopedic surgery. Various local antibiotic delivery techniques are used to reduce bone- and soft tissue-related infection. The objective of this study was to evaluate the efficacy of a new biodegradable, gentamicin-loaded poly(D,L-lactide) (PDLLA) coating of orthopedic devices in preventing implant-related osteomyelitis. The medullary cavities of tibiae in 30 Sprague Dawley rats were contaminated with Staphylococcus aureus (10(3) colony forming units). Simultaneously titanium Kirschner wires, uncoated (group II), coated with PDLLA (group III), or coated with PDLLA + 10% gentamicin (group IV), were implanted. Ten animals that received phosphate-buffered saline and uncoated Kirschner wires served as controls (group I). Follow-up was 6 weeks. In weekly intervals X-rays of the tibiae were performed, blood counts were taken, and body temperature and weight were determined. After sacrifice infection was evaluated by histological and microbiological analysis. All animals of groups II and III developed microbiological, histological, and radiological signs of infection, including osseous destruction and soft tissue swelling. All animals of the control group remained sterile. Cultures of implants of group IV showed significantly reduced bacterial growth compared to cultures of groups II and III, and three implants of group IV remained sterile. Further radiological and histological signs of infection were significantly reduced in the gentamicin-coated group compared to groups II and III. No significant differences in body weight, body temperature, and blood parameters between all groups were observed. Local application of antibiotic-coated orthopedic devices containing PDLLA and 10% gentamicin significantly reduced implant-related infection in this animal model.

Reliability of the ica, aap and atlE genes in the discrimination between invasive, colonizing and contaminant Staphylococcus epidermidis isolates in the diagnosis of catheter-related infections

OBJECTIVES

To evaluate the usefulness of detecting two genes involved in biofilm formation (icaA and aap) and one gene involved in initial adhesion (atlE) for discrimination between contaminant, colonizing and invasive Staphylococcus epidermidis isolates involved in catheter-related infections.

PATIENTS

The first group contained 29 isolates that were isolated from the skin of healthy volunteers (contaminant isolates). The second group contained 16 isolates recovered from catheters (>1000 CFUs on quantitative catheter culture) from asymptomatic patients without bacteremia. These isolates were considered to be colonizing isolates. The third group contained 34 isolates grown in >or=2 different blood cultures from patients with a systemic inflammatory response. These isolates were considered to be invasive isolates.

RESULTS

The prevalence of atlE did not differ between the three groups. The icaA and aap genes were significantly more prevalent in colonizing isolates (88% aap; 88% icaA) than in invasive isolates (68% aap, P = 0.179; 59% icaA, P = 0.055) and than in skin isolates (52% aap, P = 0.02; 38% icaA, P = 0.002).

CONCLUSIONS

The high prevalence of aap and icaA in skin isolates and their higher prevalence in colonizing than in invasive isolates led to a low specificity when these genes were used to differentiate between contamination, colonization and invasive infection. We conclude that, although the prevalence of these genes differs in the three groups, their presence cannot be used for clinical decision-making.

Shear stress and material surface effects on adherent human monocyte apoptosis

Monocytes play a critical role as both phagocytes and mediators of inflammatory responses in the prevention of cardiovascular device-related infections. However, persistent infection of these devices still occurs and may be attributed to deleterious cellular alterations resulting from monocyte interactions with a foreign material in an environment of dynamic flow. Thus, the effects of both shear stress and adhesion to material surfaces on human monocyte apoptosis were investigated. A rotating disk system generated physiologically relevant shear stress levels (0-14 dyn/cm(2)), and shear-related apoptosis occurring in adherent monocytes was characterized. Using annexin V analysis, apoptosis of polyurethane-adherent monocytes under shear for 4 h increased to levels >70% with increasing shear in a near-linear fashion (r2 = 0.713). It was qualitatively confirmed using confocal microscopy that filamentous (F)-actin distribution was altered, that DNA fragmentation occurred, and that activated caspases were involved in shear-induced apoptosis. Static studies determined that spontaneous apoptosis was material-dependent over 72 h by demonstrating marked differences between apoptosis of monocytes adherent to a polyurethane compared to an alkyl-modified glass. Treatment with TNF-alpha augmented this material dependency in a dose-dependent fashion over time. F-actin content of TNF-alpha-treated cells decreased to <62% of untreated cells. We conclude that concomitant effects from both material surfaces and dynamic flow mediate human monocyte apoptosis and may have serious implications in the context of implanted cardiovascular device infection.

Infection of orthopedic implants and the use of antibiotic-loaded bone cements. A review

Infections by bacteria are a serious complication following orthopedic implant surgery, that can usually only be cured by removing the implant, since the biofilm mode of growth of infecting bacteria on an implant surface protects the organisms from the host immune system and antibiotic therapy. Over the past few decades, attempts have been made to prevent and cure orthopedic implant infections by incorporating antibiotics in polymethylmethacrylate bone cements, in primary and revision surgery. However, the clinical efficacy of antibiotic-releasing bone cements is not accepted by all and the long-term exposure to low doses from antibiotic-releasing bone cements in patients is strongly related to the emerging threat of antibiotic resistance in medicine today. In this article, we start by reviewing the mechanisms governing the formation of an infectious biofilm on orthopedic implant materials, the release mechanisms and properties of clinically-used, antibiotic-loaded bone cements. The clinical efficacy of antibiotic-loaded bone cements is evaluated analyzing separatedly the prophylactic and therapeutic uses of these products.

Quantification of expression of Staphylococcus epidermidis housekeeping genes with Taqman quantitative PCR during in vitro growth and under different conditions

The aims of the present study were (i) to develop and test a sensitive and reproducible method for the study of gene expression in staphylococci and (ii) to study the expression of five housekeeping genes which are involved in nucleic acid metabolism (gmk, guanylate kinase; the dihydrofolate reductase [DHFR] gene), glucose metabolism (tpi, triosephosphate isomerase), and protein metabolism (the 16S rRNA gene; hsp-60, heat-shock protein 60) during in vitro exponential and stationary growth. A modified method for instant mRNA isolation was combined with gene quantification via Taqman real-time quantitative PCR. The detection limit of our method was 10 copies of RNA. The average intersample variability was 16%. A 10-fold increase in the expression of the hsp-60 gene was induced by exposure to a 10 degrees C heat shock (37 to 47 degrees C) for 10 min. During in vitro growth, the expression of all five housekeeping genes showed rapid up-regulation after inoculation of the bacteria in brain heart infusion medum and started to decline during the mid-exponential-growth phase. Maximal gene expression was 110- to 300-fold higher than gene expression during stationary phase. This indicates that housekeeping metabolism is a very dynamic process that is extremely capable of adapting to different growth conditions. Expression of the 16S rRNA gene decreases significantly earlier than that of other housekeeping genes. This confirms earlier findings for Escherichia coli that a decline in bacterial ribosomal content (measured by 16S rRNA gene expression) precedes the decline in protein synthesis (measured by mRNA expression).

Effect of plasma and matrix proteins on defensin-induced impairment of phagocytic killing by adherent neutrophils

Infection is too often associated with prosthetic devices. Increased susceptibility to infection at these surgical sites appears to be associated with defective local phagocytic killing. The mechanisms for neutrophil down-regulation, however, continue to be obscure. We have recently demonstrated that cytotoxic substances are released from granulocytes associated with materials. One group of releasants, the cationic human neutrophil peptide(s) (also called defensins) not only impairs the antimicrobial capacity of the granulocyte that releases it but also impairs bystander phagocytes. Because plasma or matrix proteins soon become associated with implants, we investigated the interactive effect of adding these proteins, singly and in combination, on the microbicidal effect of bystander cells. Some plasma/matrix proteins (whole plasma, albumin, fibrinogen, and fibronectin) strongly interfered with the anti-microbicidal effects generated by neutrophil-polystyrene interaction. Other proteins (vitronectin and laminin) were without effect. These results suggest that protein composition at the prosthetic implant site could have a significant effect on infectivity, depending on whether neutrophils releasants were attenuated. In the absence of attenuation, the local environment would be hostile to host defenses, permitting bacterial survival and proliferation.

Shear stress-induced apoptosis of adherent neutrophils: a mechanism for persistence of cardiovascular device infections

The mechanisms underlying problematic cardiovascular device-associated infections are not understood. Because the outcome of the acute response to infection is largely dependent on the function of neutrophils, the persistence of these infections suggests that neutrophil function may be compromised because of cellular responses to shear stress. A rotating disk system was used to generate physiologically relevant shear stress levels (0-18 dynes/cm(2); 1 dyne = 10 microN) at the surface of a polyetherurethane urea film. We demonstrate that shear stress diminishes phagocytic ability in neutrophils adherent to a cardiovascular device material, and causes morphological and biochemical alterations that are consistent with those described for apoptosis. Complete neutrophil apoptosis occurred at shear stress levels above 6 dynes/cm(2) after only 1 h. Morphologically, these cells displayed irreversible cytoplasmic and nuclear condensation while maintaining intact membranes. Analysis of neutrophil area and filamentous actin content demonstrated concomitant decreases in both cell area and actin content with increasing levels of shear stress. Neutrophil phagocytosis of adherent bacteria decreased with increasing shear stress. Biochemical alterations included membrane phosphatidylserine exposure and DNA fragmentation, as evaluated by in situ annexin V and terminal deoxynucleotidyltransferase-mediated dUTP end labeling (TUNEL) assays, respectively. The potency of the shear-stress effect was emphasized by comparative inductive studies with adherent neutrophils under static conditions. The combination of tumor necrosis factor-alpha and cycloheximide was ineffective in inducing >21% apoptosis after 3 h. These findings suggest a mechanism through which shear stress plays an important role in the development of bacterial infections at the sites of cardiovascular device implantation.

Surfactant polymers designed to suppress bacterial (Staphylococcus epidermidis) adhesion on biomaterials

We describe a series of surfactant polymers designed as surface-modifying agents for the suppression of bacterial adhesion on biomaterials. The surfactant polymers consist of a poly(vinyl amine) backbone with hydrophilic poly(ethylene oxide) (PEO) and hydrophobic hexanal (Hex) side chains (PVAm/PEO:Hex). Surface modification is accomplished by simple dip coating from aqueous solution, from which surfactant polymers undergo spontaneous surface-induced assembly on hydrophobic biomaterials. The stability of PVAm/PEO:Hex on pyrolytic graphite (HOPG) and polyethylene (PE) was demonstrated by the absence of detectable desorption under flow conditions of pure water over a 24-h period. PEO surfactant polymers with four different PEO:Hex ratios (1:1.4, 1:2.5, 1:4.6, and 1:10.7) and a dextran surfactant polymer were compared with respect to S. epidermidis adhesion under dynamic flow conditions. Suppression of S. epidermidis adhesion was achieved for all modified surfaces over the shear range 0-15 dyn/cm(2). The effectiveness depended on the surfactant polymer composition such that S. epidermidis adhesion to modified surfaces decreased significantly with increasing PEO packing density. Modified HOPG was more effective in reducing bacterial adhesion compared with the corresponding modification on PE, which we attribute to the presence of defects in surfactant polymer assembly on PE. Our results are discussed from the perspective of critical factors, such as optimal PEO packing density and hydration thickness, that contribute to the effectiveness of surfactant polymers to shield a biomaterial from adhesive bacterial interactions.

Antibiotics in the irrigating solutions reduce Staphylococcus epidermidis adherence to intraocular lenses

PURPOSE

To investigate the effect of antibiotics in the irrigating solutions on hydrophobicity, slime production and the adherence of Staphylococcus epidermidis to intraocular lenses (IOLs).

METHODS

A standard culture of S. epidermidis was incubated with a control phosphate-buffered saline (PBS) or PBS containing vancomycin (20 micrograms/ml) or gentamicin (8 micrograms/ml) or a combination of gentamicin and vancomycin (8 and 20 micrograms/ml, respectively) for 30, 60 and 120 min at 35 degrees C. The bacteria were harvested by centrifugation, and washed with PBS before incubation with IOLs for 1 h. Adhesion of bacterial cells to IOLs was determined by counting the viable cells attached to the lenses. Slime production on IOLs was measured using safranin staining. Hydrophobicity of the control cultures and cultures treated with antibiotics was assayed on the basis of the hexadecane droplet method.

RESULTS

Bacterial exposure to antibiotics produced a time-dependent significant decrease in bacterial hydrophobicity and adherence to IOLs compared with the untreated control cells (p < 0.001). Hydrophobicity showed a significant correlation with adherence (r = 0.89, p < 0.001). Gentamicin was significantly more effective than vancomycin, and the synergistic combination of gentamicin and vancomycin was the most effective in reducing bacterial adherence to IOLs, hydrophobicity and slime production.

CONCLUSIONS

The use of antibiotics in the irrigating solutions during cataract surgery may be useful in reducing bacterial adherence to IOLs. Further studies are needed to determine the clinical implications of these findings in reducing the incidence of post-operative endophthalmitis associated with IOL implantation.

Design of infection-resistant antibiotic-releasing polymers: I. Fabrication and formulation

Biomaterials-related infections are often observed with prosthetic implants and in many cases result in the failure of the devices. To design a biomedically useful polymer that is intrinsically infection-resistant, we have developed a ciprofloxacin-loaded polyurethane (PU) matrix that releases antibiotic locally at the implant surface, thereby minimizing bacterial accumulation. We report here the methods of fabrication and formulation for making such antibiotic-loaded devices, as well as evidence of their bactericidal properties. Specifically, various pore-forming agents and drug loadings were examined. An optimum formulation consisting of BIOSPAN PU, poly(ethylene glycol) and ciprofloxacin offered the longest effective period of sustained release (5 days). The bactericidal efficacy of the released ciprofloxacin against Pseudomonas aeruginosa (PA) was four times that of the control PU without antibiotics. This bactericidal efficiency was due to an increase in the PA detachment from the surface. These observations suggested that the released ciprofloxacin was biologically active in preventing the bacteria from permanently adhering to the substratum, and thus decreasing the possibility of biofilm-related infection.

Defensins impair phagocytic killing by neutrophils in biomaterial-related infection

The implantation of foreign material carries a risk of infection which frequently is resistant to all treatment short of removing the implant. We have previously shown that these materials activate neutrophils by contact, leading to production of oxygen free radicals accompanied by release of granule products. Such activation further results in depletion of local host defenses, including the capacity of biomaterial-activated neutrophils to kill bacteria. Among the granule products released from neutrophils are small cationic antibacterial peptides (human neutrophil peptides [HNP]) known as defensins. Here we tested the hypothesis that defensins, released from activated neutrophils onto the surface of biomaterials, might play a role in the deactivation of subsequent neutrophil populations. Incubation of neutrophils with purified HNP resulted in a dose-related impairment of stimulus-induced oxygen radical production and of phagocytic killing. Furthermore, fresh neutrophils added to biomaterial-associated neutrophils exhibited impaired phagocytic killing. This impairment could be abrogated by antibody to HNP but not by an irrelevant antibody. Taken together, these observations support the idea that neutrophils activated at a material surface can create, by means of HNP release, an environment hostile to their microbicidal function and that of their infiltrating brethren.

Bacterial surface properties of clinically isolated Staphylococcus epidermidis strains determine adhesion on polyethylene

The role of surface physiochemical properties of Staphylococcus epidermidis strains in adhesion to polyethylene (PE) was investigated under physiological flow conditions in phosphate buffered saline (PBS) and 1% platelet poor plasma (PPP). Four clinically isolated strains were divided into two groups: low and high relative hydrophobicity, and the F1198 and RP62A strains showing significantly greater hydrophobicity than the F21 and F1018 strains. In PBS, adhesion of all S. epidermidis strains was shear dependent from 0 to 15 dyn/cm2, after which adhesion becomes shear independent. Strains with higher surface hydrophobicity showed higher adhesion to PE, demonstrating the influence of bacterial surface hydrophobicity in nonspecific adhesion. Bacterial adhesion correlated well with bacterial surface hydrophobicity at low shear stresses (0-8 dyn/cm2). In 1% PPP, adhesion of all strains dramatically decreased and we found no correlation between bacterial surface hydrophobicity and adhesion. The presence of plasma proteins reduced nonspecific adhesion. S. epidermidis surface charge did not correlate with bacterial adhesion in either test media. The results suggested that S. epidermidis surface hydrophobicity may mediate nonspecific adhesion to PE at low shear stresses in protein-free media.

Cryopreserved arterial allografts used for the treatment of infected vascular grafts

In this study, 18 patients (17 men and 1 woman; mean age 61 years) with a previously infected vascular graft underwent vascular reconstruction with cryopreserved arterial allografts. Treatment consisted of first total (n = 11) or partial removal (n = 7) of infected prosthetic grafts. Revascularizations were aortoaortic (n = 2), aortobifemoral (n = 8), aortounifemoral (n = 3), femorofemoral (n = 2), iliofemoral (n = 1), or femoropopliteal (n = 2) bypasses. Four patients died postoperatively (22%)-one of septic necrosis of the allograft, one of septic rupture of the aortic anastomosis of a previous bypass, one of multiorgan failure, and one of mesenteric infarction. One allograft occluded within 30 days (5.5%), leading to an above-knee amputation. In the remaining patients, routine arteriography or duplex scan showed patent allografts. For the 14 survivors, the mean follow-up period was 20 months (range: 1-45 months). Two patients died-one of septicemia not related to the allograft, and one of multiple organ failure. Among the 12 survivors, 3 patients with non-ABO-compatible allografts developed different types of long-term alterations. One patient had a hemorrhage due to femoral allograft rupture at 45 days, and two patients had aortic allografts dilatation with mural thrombus, necessitating a prosthetic replacement in one patient. Cryopreserved allografts used for the treatment of infected vascular graft are useful in selected cases, although they are not totally resistant to infection. Patients should be followed closely to detect significant long-term alterations of the allografts.

Slime production of Staphylococcus epidermidis: increased bacterial adherence and accumulation onto pure titanium

In an in vitro study using Staphylococcus epidermidis RP 62 A, a slime-producing strain and its isogenic slime-negative mutant M7, we demonstrated that both strains adhere to pure titanium discs with significantly higher colony counts for the slime-producing strain. The colony count was dependent on temperature, time and strain. Prolonged incubation time (24 h) under growth conditions leads to higher colony counts for the slime-producing strain RP 62 A. As the slime-negative mutant M7 can adhere to, but not form multiple layers on metallic surfaces, increase of incubation time does not produce higher colony counts on the metallic surface. We conclude that slime production is important for adherence and subsequent accumulation of S. epidermidis onto pure titanium discs in vitro.

Patients with prosthetic joints: are they at risk when receiving invasive dental procedures?

Most prosthetic joint infections (PJI) are due to wound contamination at the time of surgery. Some infections occur due to the hematogenous spread of bacteria from distant sites of infection. A review of the literature falls to associate PJI with transient bacteremias from invasive dental procedures. Several authors have described conditions which, they believe, render patients with prosthetic joints more at risk for infection. Prosthetic joint patients with these "high risk" conditions have the same types of infecting organisms as other patients with PJI. This indicates that the infecting bacteria are from wound contamination or distant sites of infection and not related to dental procedure bacteremias. Based on this review, antibiotic prophylaxis is not indicated for patients with prosthetic joints when receiving invasive dental procedures, since there is no proven benefit and there are known risks involved with the use of antibiotics. However, the American Dental Association (ADA) and the American Academy of Orthopaedic Surgeons (AAOS), in an advisory statement, suggest prophylaxis for "high risk" patients. The ADA and AAOS recommend a single dose of amoxicillin, cephradine, or clindamycin when prophylaxis is selected. The dentist is ultimately responsible for making treatment recommendations for his or her patients.