Adherence of Staphylococcus aureus slime-producing strain variants to biomaterials used in orthopaedic surgery

The Influence of Patterned Surface Features on the Accumulation of Bovine Synovial Fluid-Induced Aggregates of Staphylococcus aureus

Periprosthetic joint infections occurring after joint replacement are a major clinical problem requiring repeated surgeries and antibiotic interventions. Staphylococcus aureus is the most prominent bacterium causing most implant-related infections. S. aureus can form a biofilm, which is defined as a group of attached bacteria with the formation of an envelope that is resistant to antibiotics. The attachment and retention of these bacteria on implant surfaces are not clearly understood.

Staphylococcus aureus Aggregates on Orthopedic Materials under Varying Levels of Shear Stress

Periprosthetic joint infection (PJI) occurring after artificial joint replacement is a major clinical issue requiring multiple surgeries and antibiotic interventions. Staphylococcus aureus is the bacterium most commonly responsible for PJI. Recent in vitro research has shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid (SF). We hypothesize that these aggregates provide early protection to bacteria entering the wound site, allowing them time to attach to the implant surface, leading to biofilm formation. Thus, understanding the attachment kinetics of these aggregates is critical in understanding their adhesion to various biomaterial surfaces. In this study, the number, size, and surface area coverage of aggregates as well as of single cells of S. aureus were quantified under various conditions on different orthopedic materials relevant to orthopedic surgery: stainless steel (316L), titanium (Ti), hydroxyapatite (HA), and polyethylene (PE). It was observed that, regardless of the material type, SF-induced aggregation resulted in reduced aggregate surface attachment and greater aggregate size than the single-cell populations under various shear stresses. Additionally, the surface area coverage of bacterial aggregates on PE was relatively high compared to that on other materials, which could potentially be due to the rougher surface of PE. Furthermore, increasing shear stress to 78 mPa decreased aggregate attachment to Ti and HA while increasing the aggregates' average size. Therefore, this study demonstrates that SF induced inhibition of aggregate attachment to all materials, suggesting that biofilm formation is initiated by lodging of aggregates on the surface features of implants and host tissues.IMPORTANCE Periprosthetic joint infection occurring after artificial joint replacement is a major clinical issue that require repeated surgeries and antibiotic interventions. Unfortunately, 26% of patients die within 5 years of developing these infections. Staphylococcus aureus is the bacterium most commonly responsible for this problem and can form biofilms to provide protection from antibiotics as well as the immune system. Although biofilms are evident on the infected implants, it is unclear how these are attached to the surface in the first place. Recent in vitro investigations have shown that staphylococcal strains rapidly form aggregates in the presence of synovial fluid and provide protection to bacteria, thus allowing them time to attach to the implant surface, leading to biofilm formation. In this study, we investigated the attachment kinetics of Staphylococcus aureus aggregates on different orthopedic materials. The information presented in this article will be useful in surgical management and implant design.

Implant-Associated Infection of Long-Segment Spinal Instrumentation: A Retrospective Analysis of 46 Consecutive Patients

Study Design

This single-center retrospective study analyzed patients with an implant-associated infection of spinal instrumentation (four or more segments) treated between 2010 and 2018.

Purpose

This study aimed to investigate the treatment of implant-associated infections of long-segment spinal instrumentation and to define risk factors for implant removal.

Overview of Literature

Implant-associated infection occurs in 0.7%–20% of spinal instrumentation. Significant blood loss, delayed reoperation, and use of effective antibiotics are reported risk factors for implant removal.

Methods

Patients with superficial infections not involving the implant were excluded. All patients received surgical and antibiotic treatments according to our interdisciplinary osteomyelitis board protocol. An infection was considered healed if a patient showed no signs of infection 1 year after termination of treatment. The patients were divided into an implant retention group and implant removal group, and their clinical and microbiological data were compared.

Results

Forty-six patients (27 women, 19 men) with an implant-associated infection of long-segment spinal instrumentation and mean age of 65.3±14.3 years (range, 22–89 years) were included. The mean length of the infected instrumentation was 6.5±2.4 segments (range, 4–13 segments). Implant retention was possible in 21 patients (45.7%); in the other 25 patients (54.3%), a part of or the entire implant required removal. Late infections were associated with implant removal, which correlated with longer hospitalization. Both groups showed high postoperative complication rates (50%) and high mortality rates (8.7%). In 39 patients (84.8%), infection was eradicated at a mean follow-up of 18.9±11.1 months (range, 12–60 months). Three patients (6.5%) were lost to follow-up.

Conclusions

Implant-associated infections of long-segment spinal instrumentations are associated with high complication and mortality rates. Late infections are associated with implant removal. Treatment should be interdisciplinary including orthopedic surgeons and clinical infectiologists.

Partial 2-Stage Exchange for Infected Total Hip Arthroplasty: An Updated Report

BACKGROUND

Management of an infected total hip arthroplasty (THA) is challenging. The eradication of infection as well as complications of component removal must all be considered. This study is an update on previous reports of treating periprosthetic infection of the hip with a partial 2-stage exchange with retention of the femoral component.

METHODS

A retrospective review of our practice's arthroplasty registry from 2000 to 2018 revealed 41 hips with 2-year minimum follow-up that were treated with a 2-stage partial exchange for an infected THA. All first-stage procedures allowed an articulating construct with 1 of 3 variations: cemented constrained liner (13 hips), StageOne Hip Cement Spacer Mold (14 hips), or an antibiotic polymethylmethacrylate head molded from a bulb syringe (14 hips). Of 41 cases, 34 were culture positive, with 3 cases having methicillin-resistant Staphylococcus.

RESULTS

Mean follow-up was 5.5 years (range, 1.5-18.5 years). The second-stage reimplantation was accomplished in 39 of the 41 hips (95%) at a mean interval of 9.2 weeks (range, 5-9 weeks). Two patients underwent repeat radical debridement with removal of all components before reimplantation for persistent clinical evidence of infection. Thirty-three of the 41 hips (81%) were infection free at most recent follow-up. The mean postoperative Harris hip score at most recent evaluation was 63.6 (range, 24-100).

CONCLUSION

Eradication of periprosthetic joint infections, while minimizing patient morbidity, continues to be a challenge. Partial 2-stage exchange may be considered in cases where removal of a well-fixed femoral component may result in significant bony destruction.

Implants for Vertebral Body Replacement - Which Systems are Available and Have Become Established

Since the first vertebral body replacement operations over 50 years ago until now, there were developed numerous methods and implants. Vertebral body replacement after corpectomy nowadays is a standard procedure in spinal surgery. At the beginning mainly bone grafts were used. Due to continuous development, PMMA and titanium implants were developed. Nowadays various expandable and non-expandable implants are available. Numerous implants can still be justified. The question arises which methods and systems are on the market and which ones have proven themselves? This article describes and compares the advantages and disadvantages of each implant type.

The impact of thermal cycling on Staphylococcus aureus biofilm growth on stainless steel and titanium orthopaedic plates

Background

Orthopaedic implant infections are difficult to eradicate because bacteria adhering to implant surfaces inhibit the ability of the immune system and antibiotics to combat these infections. Thermal cycling is a temperature modulation process that improves performance and longevity of materials through molecular structural reorientation, thereby increasing surface uniformity. Thermal cycling may change material surface properties that reduce the ability for bacteria to adhere to the surface of orthopaedic implants. This study aims to determine whether thermal cycling of orthopaedic implants can reduce bacterial growth.

Methods

In a randomized, blinded in-vitro study, titanium and stainless steel plates treated with thermal cycling were compared to controls. Twenty-seven treated and twenty-seven untreated plates were covered with 10 ml tryptic soy broth containing ~ 10⁵ colony forming units (CFU)/ml of bioluminescent Staphylococcus aureus (S. aureus)Xen29 and incubated at 37 °C for 14d. Quantity and viability of bacteria were characterized using bioluminescence imaging, live/dead staining and determination of CFUs.

Results

Significantly fewer CFUs grow on treated stainless steel plates compared to controls (p = 0.0088). Similar findings were seen in titanium plates (p = 0.0048) following removal of an outlier. No differences were evident in live/dead staining using confocal microscopy, or in metabolic activity determined using bioluminescence imaging (stainless steel plates: p = 0.70; titanium plates: p = 0.26).

Conclusion

This study shows a reduction in CFUs formation on thermal cycled plates in-vitro. Further in-vivo studies are necessary to investigate the influence of thermal cycling on bacterial adhesion during bone healing. Thermal cycling has demonstrated improved wear and strength, with reductions in fatigue and load to failure. The added ability to reduce bacterial adhesions demonstrates another potential benefit of thermal cycling in orthopaedics, representing an opportunity to reduce complications following fracture fixation or arthroplasty.

Animal Models of Osteomyelitis

There are numerous reports in the literature using animal models of osteomyelitis for investigating pathogenesis, diagnosis, and treatment of bone infections. Rabbits, rats, and dogs are commonly used animals, and, less frequently, chickens, guinea pigs, miniature pigs, goats, and sheep. Commonly used bones for creating local osteomyelitis include tibia, femur, and radius, and, less frequently, mandible and spine. When designing a specific model, one should consider which animal and which bone will be used, which route for inoculation (either local injection or systemically through vascular injection), which bacterial species and how many bacteria should be applied, if and what sclerosing agent, foreign body or implant should be employed, and if local trauma is needed. Basic methods of evaluation include clinical observation, radiography, microbiology, and histology.

Rapid in Vitro Quantification of S. aureus Biofilms on Vascular Graft Surfaces

Objectives: Increasing resistance of microorganisms and particularly tolerance of bacterial biofilms against antibiotics require the need for alternative antimicrobial substances. S. aureus is the most frequent pathogen causing vascular graft infections. In order to evaluate the antimicrobial efficacy, quantification of the bacterial biofilms is necessary. Aim of the present study was the validation of an in vitro model for quantification of bacterial biofilm on vascular graft surfaces using three different assays. Methods: Standardized discs of vascular graft material (Dacron or PTFE) or polystyrene (PS) as control surface with 0.25 cm² surface area were inoculated with 10^-3 diluted overnight culture of three biofilm-producing S. aureus isolates (BEB-029, BEB-295, SH1000) in 96-well PS culture plates. After incubation for 4 and 18 h, the biofilm was determined by three different methods: (a) mitochondrial ATP concentration as measure of bacterial viability (ATP), (b) crystal violet staining (Cry), and (c) vital cell count by calculation of colony-forming units (CFU). The experiments were performed three times. Quadruplicates were used for each isolate, time point, and method. In parallel, bacterial biofilms were documented via scanning electron microscopy. Results: All three methods could quantify biofilms on the PS control. Time needed was 0:40, 13:10, and 14:30 h for ATP, Cry, and CFU, respectively. The Cry assay could not be used for vascular graft surfaces due to high unspecific background staining. However, ATP assay and CFU count showed comparable results on vascular graft material and control. The correlations between ATP and CFU assay differed according to the surface and incubation time and were significant only after 4 h on Dacron (BEB-029, p = 0.013) and on PS (BEB-029, p < 0.001). Between ATP and Cry assay on PS, a significant correlation could be detected after 4 h (BEB-295, p = 0.027) and after 18 h (all three strains, p < 0.026). The reproducibility of the ATP-assay presented as inter-assay-variance of 2.1 and as intra-assay variance of 8.1 on polystyrene. Conclusion: The in-vitro model reproducibly quantifies biofilm on standardized vascular graft surfaces with ATP assay as detection system. The ATP assay allows accelerated microbial quantification, however the correlation with the CFU assay may be strain- and surface-dependent.

A novel co-culture model of murine K12 osteosarcoma cells and S. aureus on common orthopedic implant materials: 'the race to the surface' studied in vitro

Infection is a major cause of orthopedic implant failure. There are few studies assessing both tissue cell and bacterial adherence on common orthopedic implant materials in a co-culture environment. An in vitro co-culture model was created using K12 osteosarcoma cells and Staphylococcus aureus in a medium incubated over metal disks for 48 h. The results showed that, in the presence of S. aureus, there were fewer osteosarcoma cells attached to the disks for all substrata tested. There were significantly more osteosarcoma cells adhering to the cobalt chrome than the stainless steel and titanium disks. Overall, in the presence of osteosarcoma cells, there were more bacteria adhering to the disks for all the substrata tested, with significantly more bacteria adhering to the stainless steel disks compared to cobalt chrome and titanium disks. Scanning electron microscopy verified that osteosarcoma cells and bacteria were adherent to the metal disks after incubation for 48 h. Furthermore, the observation that more bacteria were in the co-culture than in the control sample suggests that the osteosarcoma cells serve as a nutrient source for the bacteria. Future models assessing the interaction of osteogenic cells with bacteria on a substratum would be improved if the model accounted for the role of the immune system in secondary bone healing.

Antibacterial activity of oxyresveratrol against methicillin-resistant Staphylococcus aureus and its mechanism

Oxyresveratrol (ORV) is a naturally occurring compound found in mulberries that exhibits a wide spectrum of biological activities. However, the underlying mechanism of the action of ORV against the methicillin-resistant S. aureus (MRSA) pathogen has not yet been reported. MRSA is multidrug-resistant, causing skin and other types of infections. The aim of the present study was to examine the antimicrobial activity of ORV and the underlying mechanism of its action on MRSA. The antibacterial activity of ORV was evaluated using a minimum inhibitory concentration (MIC) assay, and the mechanism of its antibacterial action on S. aureus was investigated using a combination of ORV with detergent, ATPase inhibitors and peptidoglycan (PGN). In addition, the survival characteristics and changes in MRSA morphology were monitored using transmission electron microscopy (TEM). The MIC value of ORV against all S. aureus strains was found to be 125 µg/ml. The optical density at 600 nm of each suspension treated using a combination of ORV with Triton X-100, N,N'-dicyclohexylcarbodiimide or sodium azide was reduced by 68.9-89.8% compared with the value upon treatment with ORV alone. In the ORV and PGN combination assay, direct binding of ORV with PGN from S. aureus was evident. Furthermore, TEM examination of MRSA treated with ORV showed alterations in septa formation. In conclusion, these results showed that ORV has a strong antibacterial effect against S. aureus, mainly by increasing membrane permeability and inhibiting ATPase when combined with other drugs.

Does the Type of Metal Instrumentation Affect the Risk of Surgical Site Infection in Pediatric Scoliosis Surgery?

STUDY DESIGN

Retrospective cohort study.

OBJECTIVES

To determine the association of implant metal composition with the risk of surgical site infection (SSI) following pediatric spine surgery.

SUMMARY OF BACKGROUND DATA

SSI is a well-described complication following pediatric spine surgery. Many risk factors have been identified in the literature, but controversy remains regarding metal composition as a risk factor.

METHODS

This was a retrospective study of patients who underwent posterior spinal instrumentation procedures between January 1, 2006, and December 31, 2008, at three large children's hospitals for any etiology of scoliosis and had at least 1 year of postoperative follow-up. Procedures included posterior spinal fusion, growth-friendly instrumentation, and revision of spinal instrumentation. The Centers for Disease Control and Prevention definition of SSI was used. A chi-squared test was performed to determine the relationship between type of metal instrumentation and development of an SSI.

RESULTS

The study included 874 patients who underwent 1,156 total procedures. Overall, 752 (65%) procedures used stainless steel instrumentation, 238 (21%) procedures used titanium instrumentation, and the remaining 166 (14%) procedures used cobalt chrome and titanium hybrid instrumentation. The overall risk of infection was 6.1% (70/1,156) per procedure, with 5.9% (44/752) for stainless steel, 6.7% (12/238) for titanium, and 6.0% (10/166) for cobalt chrome. The multiple regression analysis found no significant differences in the metal type used between patients with and without infection (p = .886) adjusting for etiology, instrumentation to pelvis, and type of procedures. When stratified based on etiology, the multiple regression analyses also found no significant difference in SSI between two metal type groups.

CONCLUSIONS

This study found no difference in risk of infection with stainless steel, titanium, or cobalt chrome/titanium instrumentation and is adequately powered to detect a true difference in risk of SSI.

LEVEL OF EVIDENCE

Level II, prognostic.

Atmospheric pressure nonthermal plasmas for bacterial biofilm prevention and eradication

Biofilms are three-dimensional structures formed by surface-attached microorganisms and their extracellular products. Biofilms formed by pathogenic microorganisms play an important role in human diseases. Higher resistance to antimicrobial agents and changes in microbial physiology make treating biofilm infections very complex. Atmospheric pressure nonthermal plasmas (NTPs) are a novel and powerful tool for antimicrobial treatment. The microbicidal activity of NTPs has an unspecific character due to the synergetic actions of bioactive components of the plasma torch, including charged particles, reactive species, and UV radiation. This review focuses on specific traits of biofilms, their role in human diseases, and those effects of NTP that are helpful for treating biofilm infections. The authors discuss NTP-based strategies for biofilm control, such as surface modifications to prevent bacterial adhesion, killing bacteria in biofilms, and biofilm destruction with NTPs. The unspecific character of microbicidal activity, proven polymer modification and destruction abilities, low toxicity for human tissues and absence of long-living toxic compounds make NTPs a very promising tool for biofilm prevention and control.

Early staphylococcal biofilm formation on solid orthopaedic implant materials: in vitro study

Biofilms forming on the surface of biomaterials can cause intractable implant-related infections. Bacterial adherence and early biofilm formation are influenced by the type of biomaterial used and the physical characteristics of implant surface. In this in vitro research, we evaluated the ability of Staphylococcus epidermidis, the main pathogen in implant-related infections, to form biofilms on the surface of the solid orthopaedic biomaterials, oxidized zirconium-niobium alloy, cobalt-chromium-molybdenum alloy (Co-Cr-Mo), titanium alloy (Ti-6Al-4V), commercially pure titanium (cp-Ti) and stainless steel. A bacterial suspension of Staphylococcus epidermidis strain RP62A (ATCC35984) was added to the surface of specimens and incubated. The stained biofilms were imaged with a digital optical microscope and the biofilm coverage rate (BCR) was calculated. The total amount of biofilm was determined with the crystal violet assay and the number of viable cells in the biofilm was counted using the plate count method. The BCR of all the biomaterials rose in proportion to culture duration. After culturing for 2-4 hours, the BCR was similar for all materials. However, after culturing for 6 hours, the BCR for Co-Cr-Mo alloy was significantly lower than for Ti-6Al-4V, cp-Ti and stainless steel (P<0.05). The absorbance value determined in the crystal violet assay and the number of viable cells on Co-Cr-Mo were not significantly lower than for the other materials (P>0.05). These results suggest that surface properties, such as hydrophobicity or the low surface free energy of Co-Cr-Mo, may have some influence in inhibiting or delaying the two-dimensional expansion of biofilm on surfaces with a similar degree of smoothness.

The Antibacterial Assay of Tectorigenin with Detergents or ATPase Inhibitors against Methicillin-Resistant Staphylococcus aureus

Tectorigenin (TTR) is an O-methylated isoflavone derived from the rhizome of Belamacanda chinensis (L.) DC. It is known to perform a wide spectrum of biological activities such as antioxidant, anti-inflammatory, anti-tumor. The aim of this study is to examine the mechanism of antibacterial activity of TTR against methicillin-resistant Staphylococcus aureus (MRSA). The anti-MRSA activity of TTR was analyzed in combination assays with detergent, ATPase inhibitors, and peptidoglycan (PGN) derived from S. aureus. Transmission electron microscopy (TEM) was used to monitor survival characteristics and changes in S. aureus morphology. The MIC values of TTR against all the tested strains were 125 μg/mL. The OD(600) of each suspension treated with a combination of Triton X-100, DCCD, and NaN₃ with TTR (1/10 × MIC) had been reduced from 68% to 80%, compared to the TTR alone. At a concentration of 125 μg/mL, PGN blocked antibacterial activity of TTR. This study indicates that anti-MRSA action of TTR is closely related to cytoplasmic membrane permeability and ABC transporter, and PGN at 125 μg/mL directly bind to and inhibit TTR at 62.5 μg/mL. These results can be important indication in study on antimicrobial activity mechanism against multidrug resistant strains.

Infection with spinal instrumentation: Review of pathogenesis, diagnosis, prevention, and management

Background:

Instrumentation has become an integral component in the management of various spinal pathologies. The rate of infection varies from 2% to 20% of all instrumented spinal procedures. Every occurrence produces patient morbidity, which may adversely affect long-term outcome and increases health care costs.

Methods:

A comprehensive review of the literature from 1990 to 2012 was performed utilizing PubMed and several key words: Infection, spine, instrumentation, implant, management, and biofilms. Articles that provided a current review of the pathogenesis, diagnosis, prevention, and management of instrumented spinal infections over the years were reviewed.

Results:

There are multiple risk factors for postoperative spinal infections. Infections in the setting of instrumentation are more difficult to diagnose and treat due to biofilm. Infections may be early or delayed. C Reactive Protein (CRP) and Magnetic Resonance Imaging (MRI) are important diagnostic tools. Optimal results are obtained with surgical debridement followed by parenteral antibiotics. Removal or replacement of hardware should be considered in delayed infections.

Conclusions:

An improved understanding of the role of biofilm and the development of newer spinal implants has provided insight in the pathogenesis and management of infected spinal implants. This literature review highlights the mechanism, pathogenesis, prevention, and management of infection after spinal instrumentation. It is important to accurately identify and treat postoperative spinal infections. The treatment is often multimodal and prolonged.

A selected screening programme was less effective in the detection of methicillin-resistant Staphylococcus aureus colonisation in an orthopaedic unit

PURPOSE

Our unit has used a selective screening policy for methicillin-resistant Staphylococcus aureus (MRSA) colonisation using standard chromogenic growth media, based upon risk stratification. The aim of this study was to examine the effectiveness of this selective screening policy.

METHODS

A cohort of 429 patients was assessed for their risk status for MRSA colonisation using both rapid polymerase chain reaction (PCR) swabs and traditional culture and sensitivity analysis. The sensitivity, specificity, positive predictive values and negative predictive values of the traditional selective approach were calculated compared to universal rapid screening.

RESULTS

One hundred eighteen patients were considered high risk and would traditionally be further screened with standard culture of swabs. The prevalence of MRSA was 15/429 (3.5%). The sensitivity of selective screening was 53% identifying eight of 15 cases. The false-negative rate was therefore 47% and seven would have been missed. PCR results were available within four to six hours, whereas culture results were only available at 24 hours for the media showing no growth and not until 72 hours for positive MRSA cases.

CONCLUSIONS

We now advocate universal screening prior to, or on admission, using this rapid PCR test, as we consider this identifies MRSA colonisation more effectively and facilitates "ring-fencing" of orthopaedic beds.

A combined pharmacodynamic quantitative and qualitative model reveals the potent activity of daptomycin and delafloxacin against Staphylococcus aureus biofilms

Biofilms are associated with persistence of Staphylococcus aureus infections and therapeutic failures. Our aim was to set up a pharmacodynamic model comparing antibiotic activities against biofilms and examining in parallel their effects on viability and biofilm mass. Biofilms of S. aureus ATCC 25923 (methicillin-sensitive S. aureus [MSSA]) or ATCC 33591 (methicillin-resistant S. aureus [MRSA]) were obtained by culture in 96-well plates for 6 h/24 h. Antibiotic activities were assessed after 24/48 h of exposure to concentrations ranging from 0.5 to 512 times the MIC. Biofilm mass and bacterial viability were quantified using crystal violet and the redox indicator resazurin. Biofilms stained with Live/Dead probes were observed by using confocal microscopy. Concentration-effect curves fitted sigmoidal regressions, with a 50% reduction toward both matrix and viability obtained at sub-MIC or low multiples of MICs against young biofilms for all antibiotics tested. Against mature biofilms, maximal efficacies and potencies were reduced, with none of the antibiotics being able to completely destroy the matrix. Delafloxacin and daptomycin were the most potent, reducing viability by more than 50% at clinically achievable concentrations against both strains, as well as reducing biofilm depth, as observed in confocal microscopy. Rifampin, tigecycline, and moxifloxacin were effective against mature MRSA biofilms, while oxacillin demonstrated activity against MSSA. Fusidic acid, vancomycin, and linezolid were less potent overall. Antibiotic activity depends on biofilm maturity and bacterial strain. The pharmacodynamic model developed allows ranking of antibiotics with respect to efficacy and potency at clinically achievable concentrations and highlights the potential utility of daptomycin and delafloxacin for the treatment of biofilm-related infections.

Immediate titanium cranioplasty after debridement and craniectomy for postcraniotomy surgical site infection

BACKGROUND

For postcraniotomy surgical site infection (SSI) involving the bone, typical management involves craniectomy, debridement, and delayed cranioplasty. Disadvantages to delayed cranioplasty include cosmetic deformity, vulnerability of unprotected brain, and risks and costs associated with an additional operation. Many authors have attempted bone flap salvage by using various techniques.

OBJECTIVE

We evaluate our experience with immediate titanium mesh cranioplasty at the time of craniectomy and debridement.

METHODS

We retrospectively reviewed SSIs in patients that underwent craniotomy for treatment of a brain tumor. These patients were treated with craniectomy, debridement, and immediate titanium mesh cranioplasty followed by antibiotics. The primary outcome was recurrent infection.

RESULTS

Twelve patients met the inclusion criteria. Risk factors for infection included preoperative radiation therapy (33%), prior craniotomy (33%), and postoperative CSF leak (25%). Median follow-up was 14 months. Ten (83%) patients had long-term resolution without recurrent infection. One patient required additional surgical debridement for persistent infection with successful placement of new titanium mesh. Another patient developed recurrent infection but opted for hospice care because of tumor progression.

CONCLUSION

This series demonstrates the safety and feasibility of performing immediate titanium cranioplasty at the time of craniectomy and debridement in patients with postcraniotomy infections. This has been shown in patients with risk factors for poor wound healing. Immediate cranioplasty avoids the drawbacks, risks, and costs of delayed cranioplasty.

Orthopedics and biofilm--what do we know? A review

Bacteria have been found to grow predominantly in biofilms. The initial stage includes the attachment of bacteria to the substratum. Bacterial growth and division then leads to the colonization of the surrounding area and the formation of the biofilm. The environment in a biofilm is not homogeneous; the bacteria in a multispecies biofilm are not randomly distributed, but rather are organized to best meet their needs.

Although there is an initial understanding on the mechanisms of biofilm-associated antimicrobial resistance, this topic is still under investigation. A variety of approaches are being explored to overcome biofilm-associated antimicrobial resistance. A greater understanding of biofilm processes should lead to novel, effective control strategies for biofilm control and a resulting improvement in patient management.

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.

Effects of electrodeposited poly(ethylene glycol) on biofilm adherence to titanium

Protein-resistant coatings have been studied for inhibiting biofilm formation on implant devices. In this study, titanium (Ti) surfaces were biofunctionalized with poly(ethylene glycol) (PEG) by electrodeposition and were evaluated as biofilm substrates under an oral simulated environment. Streptococcus gordonii, an early colonizer of oral biofilms, was inoculated on Ti and PEG-electrodeposited Ti (PEG-Ti) surfaces and was analyzed quantitatively and topographically. Streptococcus mutans supplemented with sucrose, a late colonizer mainly found in dental plaque, was also used to form biofilms on the surfaces of Ti and PEG-Ti for 20 h followed by sonication as a means of detaching the biofilms. The results indicated that the attachment of S. gordonii on PEG-Ti surfaces was inhibited compared with Ti, and the S. mutans biofilm was easier to be detached from the surface of PEG-Ti than that of Ti. Moreover, the presence of PEG electrodeposited on Ti surface inhibited salivary protein adsorption. The degree of detachment of biofilms from PEG-Ti was associated with the inhibition of the salivary protein adsorption, suggesting weak basal attachment of the biofilms to the electrodeposited surfaces. Therefore, controlling protein adsorption at the initial stage of biofilm formation may be an effective strategy to protect metal surfaces from bacterial contamination not only in dental manipulations but also in orthopedic applications.

Kyphotic angle progression of thoracic and thoracolumbar tuberculous spondylitis after surgical treatment: comparison with predicted kyphosis outcome after conservative treatment

Study Design

Retrospective comparative study.

Purpose

To compare the progression of the kyphotic angle (KA) in a surgically treated group with the predicted outcome of a conservatively treated group.

Overview of Literature

Late onset kyphosis is a complication of tuberculous spondylitis making its prevention a major goal of surgery.

Methods

Twenty six consecutive patients underwent an anterior reconstruction and posterior instrumented fusion in conjunction with antituberculous chemotherapy. The mean follow up was 56 months (range, 28 to 112 months). The patients were divided into subgroups based on the involved region of the thoracic and the thoracolumbar spine, initial KA, and the initial vertebral body loss (VBL(x)). The predicted KA (KA_Pd) was calculated using the formula, KA_Pd=5.5+30.5 VBL(x), to predict the final gibbus deformity. Kyphotic angle progression (ΔKA) based on the radiographic measurements after surgery (ΔKA_R), and the predicted outcome of conservative treatment (ΔKA_P) with chemotherapy were compared.

Results

Among the subgroups of the regions involved and initial KA, the ΔKA was radiographically superior with a reduced amount of kyphogenesis in the surgery group than the predicted outcome of the conservatively treated patients (p<0.05). The radiographic ΔKA was similar (p>0.05) with VBL(x)≤0.5 in the VBL(x) subgroup.

Conclusions

These results showed that in the VBL(x) subgroup, an initial VBL(x)≤0.5 is an indication of conservative antituberculous chemotherapy without surgery.

Bactericidal behaviour of Ti6Al4V surfaces after exposure to UV-C light

TiO(2)-coated biomaterials that have been excited with UV irradiation have demonstrated biocidal properties in environmental applications, including drinking water decontamination. However, this procedure has not been successfully applied towards the killing of pathogens on medical titanium-based implants, mainly because of practical concerns related to irradiating the inserted biomaterial in situ. Previous researchers assumed that the photocatalysis on the TiO(2) surface during UV application causes the bactericidal effects. However, we show that a residual post-irradiation bactericidal effect exists on the surface of Ti6Al4V, not related with photocatalysis. Using a combination of staining, serial dilutions, and a biofilm assay, we show a significant and time-dependent loss in viability of different bacterial strains of Staphylococcus epidermidis and Staphylococcus aureus on the post-irradiated surface. Although the duration of this antimicrobial effect depends on the strains selected, our experiments suggest that the effect lasts at least 60 min after surface irradiation. The origin of such phenomena is discussed in terms of the physical properties of the irradiated surfaces, which include the emission of energy and changes in surfaces charge occurring during electron-hole recombination processes. The method here proposed for the preparation of antimicrobial titanium surfaces could become especially useful in total implant surgery for which the antimicrobial challenge is mainly during or shortly after surgery.

Quantitative analysis of Staphylococcus epidermidis biofilm on the surface of biomaterial

BACKGROUND

Staphylococcus epidermidis biofilm is considered to be an important cause of device-related infection. Polysaccharide intercellular adhesin (PIA), encoded by the icaADBC locus, has been found to be a functional component of S. epidermidis biofilm, but the sequential change of the ica gene expression during biofilm development is still unclear. We have established a quantitative experiment of biofilm formation on nontranslucent biomaterial surfaces using the biofilm coverage rate (BCR). In this study, we quantified the time course of biofilm formation on a biomaterial (stainless steel) surface by means of BCR, viable cell count (VCC) with colony-forming units, and ATP-bioluminescence (ATP) as relative light units, and investigated the time-course relationship between biofilm development process and ica gene expression using reverse transcription-polymerase chain reaction (RT-PCR).

METHODS

S. epidermidis RP62A was inoculated on stainless steel washers and incubated for 0-8, 24, and 48 h. Biofilms attached to the washers were quantified by means of BCR, VCC, and ATP. RT-PCR of the ica gene was performed using total RNA isolated from biofilms at each incubation period. Results of these methods were compared.

RESULTS

The amount of biofilms measured by BCR increased over time and particularly grew at 5-6 h into the incubation period. On the other hand, the results of VCC and ATP increased gradually, and at 24 h or 48 h the measurement values were very much greater than previously. Up to 8 h, there were significant correlations between BCR and VCC or ATP. The growth of BCR until 6 h is supported by RT-PCR of the ica gene.

CONCLUSIONS

Compared with each result, two-dimensional biofilm occupation on a biomaterial surface is proposed to be rapidly completed within 6-8 h after bacterial attachment. Our data indicate that bacterial biofilms first grow two dimensionally with a producing matrix, and subsequently grow vertically and become mature.

Effect of age on cytokine response in an experimental model of osteomyelitis

To study the effect of age on cytokine response in an experimental model of osteomyelitis. Forty adult male Wistar rats received a stainless steel needle, intramedullarly in the left tibia. Young rats (3 months old) and old rats (22 months old) were allotted in: Group A: Sterile implant. Group B: Sterile implant + slime producing S. aureus. Rats were sacrificed 9 weeks after surgery. Determinations: Cytokines (ELISA) in blood and in tibia extract and the number of bacteria in tibia and implant. The Wilcoxon, Mann-Whitney U tests were used (P < or = 0.01 significant). Infection was detected in every old rat receiving S. aureus, and in 7 of 10 young rats. In blood: prior to surgery, old rats presented higher IL-2 and lower IL-4 levels. Surgery alone did not induce significant changes in old rats; surgery + S. aureus induced significant increases of IL-2 and IL-10 in young rats, and of IL-6 in old rats. Tibia analysis S. aureus group showed increased levels of: IL-10 in young rats, and IL-1beta in old rats. In experimentally induced osteomyelitis, significant differences were observed in cytokine response with regard to age.

Beneficial influence of titanium mesh cage on infection healing and spinal reconstruction in hematogenous septic spondylitis: a retrospective analysis of surgical outcome of twenty-five consecutive cases and review of literature

STUDY DESIGN

Single institution, single surgeon retrospective review.

OBJECTIVE

To investigate if the use of titanium mesh cage on the site of infection could be beneficial for successful outcome of the operative treatment for pyogenic spondylitis.

SUMMARY OF BACKGROUND DATA

There is a controversy concerning the optimal treatment for pyogenic spondylitis regarding approach, instrumentation and staging. This large series reports on single-stage instrumented open and minimally invasive surgery for septic spondylitis.

METHODS

Twenty-four patients aged 57 +/- 16 years suffering from persistent or complicated septic spondylitis were treated by a total of 25 single stage combined surgeries (first: anterior debridement/partial vertebrectomy plus mesh cage filled with autologous bone graft; second: pedicle screw fixation with open and minimal invasive techniques). The indications for surgery included neurologic compromise, significant vertebral body destruction with kyphosis associated with segmental instability, failure of medical treatment, and/or epidural/ paravertebral abscess formation. Needle biopsy was performed in all patients before surgery. Patients were evaluated before and after surgery in terms of pain and neurologic level, sagittal segmental spinal balance, radiologic fusion and recovery.

RESULTS

All but 1 tetraplegic patient with simultaneous cervical and lumbar spondylitis, who died because of massive clot lung embolism 2 months after surgery, were followed for 56 months (range, 31-116 months) The visual analogue scale score improved from 6.5 before surgery to 1.8 after surgery. The segmental kyphotic deformity was corrected at an average of 6 degrees, without cage settling. An insignificant loss of kyphosis correction of an average 0.6 degrees was measured in the thoracolumbar junction only. Blood loss, surgical time, and surgical complications were significant less in the patients who operated with minimal invasive technique. Patients with incomplete neurologic impairment improved after surgery. Physical function (SF-36) averaged 72 1 year after surgery. All operated patients had resolution of infection. There was neither migration of mesh cage nor posterior instrumentation failure at the last follow-up observation.

CONCLUSION

The present study showed that radical debridement of spinal infection and anterior insertion of titanium cage, filled with autogenous bone graft, secured with pedicle screw instrumentation should have had a beneficial influence on the eradication of infection, segmental and global spinal reconstruction and fusion. Supplementary posterior minimal invasive pedicle screw fixation eliminates posterior soft tissue injury and preserves blood supply, and reduces surgical time, blood loss, and surgical complications.

The role of small-colony variants in failure to diagnose and treat biofilm infections in orthopedics

Biomaterial-related infection of joint replacements is the second most common cause of implant failure, with serious consequences. Chronically infected replacements cannot be treated without removal of the implant, as the biofilm mode of growth protects the bacteria against antibiotics. This review discusses biofilm formation on joint replacements and the important clinical phenomenon of small-colony variants (SCVs). These slow-growing phenotypic variants often remain undetected or are misdiagnosed using hospital microbiological analyses due to their unusual morphological appearance and biochemical reactions. In addition, SCVs make the infection difficult to eradicate. They often lead to recurrence since they respond poorly to standard antibiotic treatment and can sometimes survive intracellularly.

Staphylococcus aureus adhesion to standard micro-rough and electropolished implant materials

Implant-associated infections can cause serious complications including osteomyelitis and soft tissue damage, and are a great problem due to the emergence of antibiotic resistant bacteria such as methicillin-resistant Staphylococcus aureus (MRSA). In some cases, antibiotic-loaded beads which release the antibiotic locally have been used, however such systems may lead to the development of antibiotic-resistant bacteria, as seen with gentamicin-loaded beads. Hence modifying the actual metal implant surface to inhibit or reduce initial bacterial adhesion may be an alternative option. This study describes the visualisation and quantification of S. aureus adhering to standard micro-rough 'commercially pure' titanium (TS) and Ti-6Al-7Nb (NS) surfaces, electropolished titanium (TE) and Ti-6Al-7Nb (NE) surfaces, and standard electropolished stainless steel (SS). Qualitative and quantitative results of S. aureus on the different surfaces correlated with each other, and showed significantly more live bacteria on NS than on the other surfaces, whilst there was no significant difference between the amount of bacteria on TS, TE, NE and SS surfaces. The results showed a significant decrease in the amount of bacteria adhering to the NE compared to standard NS surfaces. Such an observation suggests that the NS surface encouraged S. aureus adhesion, and could lead to higher infection rates in vivo. Hence electropolishing Ti-6Al-7Nb surfaces could be advantageous in osteosynthesis areas in minimising bacterial adhesion and lowering the rate of infection.

Staphylococcus aureus, the major pathogen in orthopaedic and cardiac surgical site infections: a literature review

Due to the increasing number of orthopaedic and cardiac procedures, these units are considered as high-risk areas because of the potentially serious consequences of surgical site infections (SSI), primarily caused by Staphylococcus aureus. The goal of this review was to evaluate the impact of S. aureus on the incidence of SSI in these high risk wards. Studies were identified by a search on the MEDLINE literature using the following mesh terms: S. aureus, cardiac, orthopaedic, surgery, SSI. Beside, data from different surveillance systems were also included. Overall, biological investigation was performed only on a small proportion of identified SSIs. Of those identified, S. aureus represented the most common pathogen accounting for approximately 20% of all SSIs. Of the 59,274 hip prostheses reported from the HELICS surveillance network, S. aureus formed 48.6% of the pathogens (416 bacteria isolated). Similarly, it represented 43.7% of pathogens after coronary artery bypass grafting. Although S. aureus turned out to be the major pathogen, this work identifies the relative lack of knowledge on the overall incidence of S. aureus infections and on the impact of this pathogenic agent when taking into consideration the degree of wound contamination and category of SSI. There is a need for more detailed information on the role of S. aureus in the burden of surgical site infections and consequently how to establish multiple approach prevention programs.

New quantitative image analysis of staphylococcal biofilms on the surfaces of nontranslucent metallic biomaterials

BACKGROUND

Implant-related infection after orthopedic surgery is difficult to cure. One of the causes of infection is the bacterial biofilm that forms around biomaterials used during surgery. Therefore, it is necessary to investigate bacterial biofilms extensively to resolve the problems of these postoperative infections. However, no established culture method or quantification system exists for bacterial biofilms grown on the surface of the metallic biomaterials used in orthopedics, which are nonradiolucent. The purpose of this study was to develop a quantitative method to evaluate the difference in resistance of stainless steel versus titanium to staphylococcal biofilms and the efficacy of antibiotics against biofilms.

METHODS

The bacterial strains used in this study were three Staphylococcus aureus stains: strain Seattle 1945 and two clinical strains cultured from postoperative infections. Staphylococcal biofilms were formed on stainless steel washers (SUS304) and titanium washers (pure titanium). They were stained with crystal violet and were examined with a digital microscope to calculate the bacterial coverage rate (BCR) by NIH imaging.

RESULTS

The BCR of S. aureus biofilms formed on stainless steel and titanium washers increased over time. At 24, 48, and 72 h after cultivation, the amount of biofilm on the surface of the stainless steel washers was significantly greater or tended to be greater than that on the titanium. Cefazolin was applied to the obtained biofilms of two clinically isolated S. aureus strains. Cefazolin did not eradicate the biofilms but significantly reduced the biofilm of one strain.

CONCLUSION

The newly developed quantitative method (static microtube culture and measurement system) was useful for assessing the amount of bacterial biofilms on the surface of nontranslucent biomaterial. We found that titanium may be more resistant to bacterial infection than stainless steel. To control implant-related severe infections, the biomaterials should be assessed from the viewpoint of their resistibility to bacterial adhesions and infections.

Interleukin-1, interleukin-6, and interleukin-10 responses after antibiotic treatment in experimental chronic Staphylococcus aureus osteomyelitis

BACKGROUND

Staphylococcal implant infections' response to treatment may be correlated with cytokine production. We investigated the effect of certain antibiotics on the cytokine response in experimental osteomyelitis.

METHODS

A stainless steel needle with an adherent slime-producing Staphylococcus aureus was implanted intramedullarly in the left tibia of 40 adult male Wistar rats. At 42 days after implantation, cefuroxime, vancomycin, tobramycin, and ciprofloxacin were administered intramuscularly every 12 h for 21 days. The control group was given no antibiotic. At the end of the treatment, implants and tibias were retrieved, and the bacterial numbers were estimated. Cytokines [interleukin-1alpha (IL-1alpha), IL-6, and IL-10] were determined (ELISA) in the tibial extract.

RESULTS

Vancomycin and cefuroxime inhibited bone colonization in all tibias, and tobramycin and ciprofloxacin inhibited it only partially. Cefuroxime reduced the number of bacteria that adhered to the implants more than the other antibiotics. IL-1alpha and IL-6 showed higher levels in the ciprofloxacin-treated group than in the cefuroxime-treated and control groups. IL-6 levels in rats treated with cefuroxime were lower than in rats treated with tobramycin or vancomycin and the control group. Cefuroxime decreased IL-10 levels more than ciprofloxacin or vancomycin or those seen in the control group.

CONCLUSIONS

The cefuroxime group showed the greatest decrease of pro-inflammatory cytokines. Different antibiotics produce different cytokine reactions that should be studied to choose the best treatment.

Staphylococci and implant surfaces: a review

Surfaces of internal fracture fixation implants are generally designed to encourage soft- and/or hard-tissue adherence, eventually leading to tissue or osseo integration. Unfortunately, this feature may also encourage bacterial adhesion. About half of the two million cases of nosocomial infections per year in the US are associated with indwelling devices. In the UK, implant-associated infections are estimated to cost pound 7-11 million per year, and with the rise in antibiotic-resistant bacteria, are an important issue. Soft-tissue infections and osteomyelitis are serious complications associated with implants, particularly open fractures, external fixation devices, and intramedullary nailing. Consequences of implant-associated infections include prolonged hospitalization with systemic antibiotic therapy, several revision procedures, possible amputation, and even death. This review discusses the issue of implant-associated infections and some of the methods used to prevent bacterial adhesion to osteosynthesis implants.

Contaminant seeding in bone by different irrigation methods: an experimental study

OBJECTIVE

This study was designed to investigate the effectiveness of using various devices and manual procedures for cleansing bacterially contaminated bone tissue and to assess the risk of iatrogenic bacterial seeding in deep bone layers.

METHODS

In an in vitro model, human femoral heads were contaminated with Escherichia coli and then cleansed with pulsatile high-pressure lavage, pulsatile low-pressure lavage, manual rinsing with bulb syringe lavage, or manual rinsing with combined brush cleaning. The numbers of bacteria that remained or those that were introduced by the rinsing procedures were quantitatively determined at depths of 0 to 1 cm, 1 to 2 cm, and 2 to 3 cm.

RESULTS

Both pulsatile high-pressure lavage and brush cleaning were more effective than pulsatile low-pressure lavage and bulb syringe lavage for the purpose of surface cleansing. The differences were highly significant (P < 0.001). There was no significant difference in the decontaminating effect between pulsatile high-pressure lavage and brush cleaning (P = 0.24). The bacterial contamination attributable to the cleansing procedure, as measured at tissue depths of 1 to 2 cm and 2 to 3 cm, was significantly higher after pulsatile high-pressure lavage and after pulsatile low-pressure lavage than it was after bulb syringe lavage or brush cleaning (P < 0.001).

CONCLUSION

In this in vitro investigation of cancellous bone, the brush cleansing was just as effective for getting rid of bacterial contamination as pulsatile high-pressure lavage, and carries a significantly lesser risk of iatrogenic bacterial seeding into deeper tissue layers. In the light of these promising results obtained by the cleansing of cancellous bone contaminated with bacteria, it would be desirable to perform supplementary in vitro and in vivo investigations into brush cleansing.

Glucose in bronchial aspirates increases the risk of respiratory MRSA in intubated patients

BACKGROUND

The risk of nosocomial infection is increased in critically ill patients by stress hyperglycaemia. Glucose is not normally detectable in airway secretions but appears as blood glucose levels exceed 6.7-9.7 mmol/l. We hypothesise that the presence of glucose in airway secretions in these patients predisposes to respiratory infection.

METHODS

An association between glucose in bronchial aspirates and nosocomial respiratory infection was examined in 98 critically ill patients. Patients were included if they were expected to require ventilation for more than 48 hours. Bronchial aspirates were analysed for glucose and sent twice weekly for microbiological analysis and whenever an infection was suspected.

RESULTS

Glucose was detected in bronchial aspirates of 58 of the 98 patients. These patients were more likely to have pathogenic bacteria than patients without glucose detected in bronchial aspirates (relative risk 2.4 (95% CI 1.5 to 3.8)). Patients with glucose were much more likely to have methicillin resistant Staphylococcus aureus (MRSA) than those without glucose in bronchial aspirates (relative risk 2.1 (95% CI 1.2 to 3.8)). Patients who became colonised or infected with MRSA had more infiltrates on their chest radiograph (p<0.001), an increased C reactive protein level (p<0.05), and a longer stay in the intensive care unit (p<0.01). Length of stay did not determine which patients acquired MRSA.

CONCLUSION

The results imply a relationship between the presence of glucose in the airway and a risk of colonisation or infection with pathogenic bacteria including MRSA.

Adherence and biofilm formation of Staphylococcus epidermidis and Mycobacterium tuberculosis on various spinal implants

STUDY DESIGN

Bacterial adherence and biofilm formation in implant-associated infection may vary depending on species of microorganisms and characteristics of implant surfaces.

OBJECTIVES

We evaluated the differences in adherence and biofilm formation between Staphylococcus epidermidis and Mycobacterium tuberculosis on various spinal implant surfaces.

SUMMARY OF BACKGROUND DATA

In implant-associated infections, bacteria in biofilm are resistant to antibiotics or host defense mechanism. The removal of implants is usually necessary to eradicate infection. On the contrary, in tuberculous infection, complete debridement and antituberculous chemotherapy without removal of implant have been regarded as a safe procedure.

METHODS

S. epidermidis and M. tuberculosis were cultured with 4 types of metal segments, smooth or rough-surfaced stainless steel, and titanium alloy, respectively. After isolation of colonized microorganisms and biofilm with trypsin treatment and culture on plate media, colony-forming units were counted. The features of adherence and biofilm formation were observed under scanning electron microscopy.

RESULTS

Biofilm-forming S. epidermidis showed heavy adhesion and multiplication on the surface of all 4 metal segments, 16.5 times more colony-forming units than nonbiofilm-forming ones. On scanning electron microscopy, there were many aggregated microcolonies with thick biofilm in biofilm-forming S. epidermidis but much less in nonbiofilm-forming S. epidermidis. M. tuberculosis were rarely adhered to metal surfaces and showed scanty biofilm formation.

CONCLUSIONS

On the contrary to S. epidermidis, adherence and biofilm formation of M. tuberculosis on implant surface are less likely, and it can provide the basis of successful instrumentation in spine tuberculosis.

Formation of Propionibacterium acnes biofilms on orthopaedic biomaterials and their susceptibility to antimicrobials

Failure to treat and eradicate prosthetic hip infection with systemic antibiotic regimens is usually due to the fact that the infection is associated with biofilm formation and that bacterial cells growing within a biofilm exhibit increased resistance to antimicrobial agents. In this in vitro study, we investigated the susceptibility of prosthetic hip Propionibacterium acnes and Staphylococcus spp. isolates growing within biofilms on polymethylmethacrylate (PMMA) bone cement to a range of antibiotics. All P. acnes isolates in the biofilm mode of growth demonstrated considerably greater resistance to cefamandole, ciprofloxacin and vancomycin. In contrast, only four of the eight P. acnes isolates demonstrated an increase in resistance to gentamicin. All ten Staphylococcus spp. isolates in the biofilm mode of growth exhibited large increases in resistance to gentamicin and cefamandole with eight of the ten isolates also exhibiting an increase in resistance to vancomycin. However, only three of the ten Staphylococcus spp. isolates exhibited an increase in resistance to ciprofloxacin. Biofilms were also formed on three different titanium alloys and on PMMA bone cement using P. acnes, Staphylococcus epidermidis and Staphylococcus aureus strains to determine if the underlying biomaterial surface had an effect on biofilm formation and the antimicrobial susceptibility of the bacteria growing within biofilms. Although differences in the rate at which the three strains adhered to the different biomaterials were apparent, no differences in biofilm antibiotic resistance between the biomaterials were observed. In the light of these results, it is important that the efficacy of other antibiotics against P. acnes and Staphylococcus spp. prosthetic hip isolates growing within biofilms on orthopaedic biomaterials be determined to ensure optimal treatment of orthopaedic implant infection.

Experimental osteomyelitis treatment with antibiotic-impregnated hydroxyapatite

A calcium hydroxyapatite antibiotic implant was evaluated to determine its efficacy as an antibiotic delivery system in a localized osteomyelitis rabbit model. Localized rabbit tibial osteomyelitis was developed with an intramedullary injection of methicillin resistant Staphylococcus aureus. Infected rabbits were randomized and divided into eight groups depending on treatment with or without debridement, systemic antibiotics, antibiotic-impregnated polymethylmethacrylate beads, or calcium hydroxyapatite implants with and without antibiotic impregnation. All treatments began 2 weeks after infection. After 4 weeks of therapy, the involved bones were cultured for concentrations of Staphylococcus aureus per gram of bone. Rabbits (n = 11) that had calcium hydroxyapatite (impregnated with vancomycin) implanted into the dead space after the debridement surgery had an 81.8% infection clearance after treatment. Rabbits (n = 10) that had polymethylmethacrylate beads (impregnated with vancomycin) implanted into the dead space after debridement surgery had a 70% clearance rate. All other treatment modalities resulted in less than 50% clearance rates. Calcium hydroxyapatite may be an effective alternative to polymethylmethacrylate for providing local antibiotic therapy in cases of methicillin resistant Staphylococcus aureus osteomyelitis.

Attachment of Staphylococcus aureus to eukaryotic cells and experimental pitfalls in staphylococcal adherence assays: a critical appraisal

Staphylococcus aureus is a bacterial species with pathogenic potential to both humans and animals. The primary natural niche is said to be the human vestibulum nasi from where bacterial cells may spread to the environment or additional anatomical sites such as the perineum or the hands, where residence is usually transient. Apparently, S. aureus is capable of a precise and balanced interaction with specific types of eukaryotic nasal cells. Although a wide variety of important bacterial ligands and possible eukaryote receptors have been described, the precise mechanisms leading to persistent bacterial colonization and, even more importantly, associated infection have not yet been elucidated in detail. This may be a consequence of the fact that most of the adherence factors have been studied individually in simplified in vitro systems, not taking the complexity of multi-factorial in vivo cell-cell interactions into account. An overall scheme of the initial and sequential interactions leading to S. aureus colonization of eukaryotic cell surfaces has not yet emerged. This review concisely describes the current state of affairs in the multi-disciplinary field of staphylococcal adherence research. Specific emphasis is placed upon the pros and cons of the various artificial, mostly in vitro models employed to study the interaction between bacterial and human or animal cells.

Evaluation of four experimental osteomyelitis infection models by using precolonized implants and bacterial suspensions

Staphylococcus aureus osteomyelitis, a major problem in orthopedic surgery, often involves biofilm bacteria adhering to implants and surrounding bone and tissues. The inadequacy of therapy or immunological surveillance has encouraged studies using animal models which simulate natural osteomyelitic infections, ensure the development of infections and avoid mortality. We evaluated 4 models for infection (8 animals/model) in rats, using stainless-steel implants in tibiae and a very adherent slime-producing bacterial strain. Each animal received: an implant containing a 12 h-biofilm with about 10(6) cfu (Model 1); an implant containing this biofilm and a suspension with about 10(4) cfu (Model 2): a sterile implant and a suspension with about 10(5) cfu (Model 3); or a sterile implant and a suspension with about 10(6) cfu (Model 4). 63 days after surgery we found 100% rat survival, colonization of bone by implant biofilm bacteria in some animals and local, but not systemic infections. Model 1 (but not Models 2-4) reproduced an infection in both, tibiae and implants, most reliably (in 100% of the animals). Model 3 was the least reliable (p < 0.01, 25% infected implants, 12% infected tibiae).

A simple infection model using pre-colonized implants to reproduce rat chronic Staphylococcus aureus osteomyelitis and study antibiotic treatment

Staphylococcus aureus biofilms formed on medical implants represent a serious problem, being difficult to eradicate with antibiotic therapy and leading to chronic infections. Simplified in vivo and in vitro antibiotic susceptibility assays using biofilm bacteria are needed. In this work, a novel chronic osteomyelitis infection model was developed in rats in the absence of bacterial suspension, requiring the use of only 10(6) bacteria in biofilms at the site of surgery, with a full success in reproducing infection. Stainless-steel implants pre-colonized for 12 h with a highly adherent S. aureaus isolate were introduced into the rat tibiae. In animals not submitted to antibiotic treatment, infection was found in the implants and spread to bone in all cases, indicating the high efficacy of the model to reproduce osteomyelitis. The effect of a 21-day treatment with cefuroxime, vancomycin, tobramycin or ciprofloxacin on infection was studied in this model 42 days after surgery. Bone colonization was inhibited by vancomycin and cefuroxime. Cefuroxime (the most efficient antibiotic, able to sterilize 1 out of 8 implants) reduced the number of bacteria in biofilms adhered to implants at a higher extent than vancomycin, trobramycin and ciprofloxacin. Analogous observations were made in this work in vivo and in vitro on the relative antibiotic efficacy against S. aureus biofilm bacteria. suggesting the usefulness of both tests as a potential tool to study antibiotic suceptibility, and the need for new antimicrobials against these bacteria.

Bap, a Staphylococcus aureus surface protein involved in biofilm formation

Identification of new genes involved in biofilm formation is needed to understand the molecular basis of strain variation and the pathogenic mechanisms implicated in chronic staphylococcal infections. A biofilm-producing Staphylococcus aureus isolate was used to generate biofilm-negative transposon (Tn917) insertion mutants. Two mutants were found with a significant decrease in attachment to inert surfaces (early adherence), intercellular adhesion, and biofilm formation. The transposon was inserted at the same locus in both mutants. This locus (bap [for biofilm associated protein]) encodes a novel cell wall associated protein of 2,276 amino acids (Bap), which shows global organizational similarities to surface proteins of gram-negative (Pseudomonas aeruginosa and Salmonella enterica serovar Typhi) and gram-positive (Enteroccocus faecalis) microorganisms. Bap's core region represents 52% of the protein and consists of 13 successive nearly identical repeats, each containing 86 amino acids. bap was present in a small fraction of bovine mastitis isolates (5% of the 350 S. aureus isolates tested), but it was absent from the 75 clinical human S. aureus isolates analyzed. All staphylococcal isolates harboring bap were highly adherent and strong biofilm producers. In a mouse infection model bap was involved in pathogenesis, causing a persistent infection.

High and low pressure pulsatile lavage of contaminated tibial fractures: an in vitro study of bacterial adherence and bone damage

OBJECTIVE

This study was designed to examine the effect of pulsatile irrigation on microscopic bone architecture and its time-dependent efficacy in removing adherent slime-producing bacteria from cortical bone.

DESIGN

Using an in vitro model, ten-millimeter transverse cut sections from five human tibiae were contaminated with Staphylococcus aureus and subjected to either high pressure pulsatile lavage (HPPL; seventy pounds per square inch, normal saline) or low pressure pulsatile lavage (LPPL; fourteen pounds per square inch, normal saline) or served as controls. Alteration of bony architecture was quantified by using a previously described ordinal scale and histomorphometric analysis of each transverse cut section of tibia. To assess the time-dependent effectiveness of pulsatile lavage in removing adherent bacteria from bone, ten-millimeter transverse cut sections from ten canine tibiae were contaminated with S. aureus and subjected to high or low pressure pulsatile lavage immediately or after one, three, or six hours. Scanning electron microscopy and bacterial cultures were used to assess the removal of adherent bacteria.

RESULTS

HPPL resulted in significantly greater macroscopic damage than was seen with LPPL or in controls (ANOVA, p < 0.001). Histomorphometry revealed that HPPL was associated with significantly larger and more numerous fissures or defects in the cortical bone when compared with low pressure irrigation (p < 0.001). However, high and low pressure lavage were associated with similar degrees of periosteal separation from the cortical bone surface (p = 0.87). Both high and low pressure lavage were effective in removing adherent bacteria from bone at three hours irrigation delay, but only high pressure lavage removed adherent bacteria from bone at six hours delay.

CONCLUSION

In this in vitro study, compared with HPPL, LPPL led to less structural damage and was equally effective in removing bacteria within three hours debridement delay; however, the efficacy of LPPL at six hours debridement delay is questionable. This finding may have clinical significance in the development of infection following open tibial fractures.