Prosthetic joint infection

Noncontact Electrical Permittivity Mapping and pH-Sensitive Films for Osseointegrated Prosthesis and Infection Monitoring

The objective of this paper is to develop a noncontact, noninvasive system for detecting and monitoring subcutaneous infection occurring at the tissue and osseointegrated prosthesis interface. It is known that the local pH of tissue can change due to infection. Therefore, the sensing system integrates two parts, namely, pH-sensitive thin films that can be coated onto prosthesis surfaces prior to them being implanted and an electrical capacitance tomography (ECT) algorithm that can reconstruct the spatial permittivity distribution of a region of space in a noncontact fashion. First, a thin film pH sensor was fabricated by spray coating, and tests confirmed that the film exhibited changes in its permittivity due to pH. Second, the ECT forward and inverse problems were implemented. Third, an aluminum rod was employed as a representative phantom of an osseointegrated prosthesis and then spray coated with the pH sensor. Finally, the film-coated phantom was immersed in different pH buffers, dried, and subjected to ECT interrogation and spatial permittivity reconstruction. The results validated that ECT was able to detect and localize permittivity variations correlated to pH changes.

Influence of exposure time on the release of bacteria from a biofilm on Ti6Al4V discs using sonication: An in vitro model

Implant sonication is considered a useful method for the diagnosis of implant-related infections. We designed an in vitro study using Ti6Al4V discs and 5 different bacteria to determine the optimal sonication time for recovery of most bacteria tested to enable use of sonication in clinical practice for microbiological diagnosis of implant-related infections. We carried out a specific protocol for the adherence and subsequent biofilm formation on the materials used. The discs were then sonicated and the retrieved bacteria were quantified. From minute 1 to 5, the amount of recovered organisms grew progressively for all bacteria. Between minute 6 and minute 10, the number was irregular for all strains except E. coli, though no pattern was evidenced. E. coli was the only microorganism with a progressive increase in liberation throughout the process. Significant differences were observed in each of the 10minutes analyzed as concerns the release of the 5 strains (P<0.021) as well as in the mean dislodgement (of the 10minutes) of all tested strains (P<0.00001). Considering that infections in which biofilms are involved could be polymicrobial, we concluded that 5minutes is the optimal time of sonication in order to recover the maximum amount of most bacteria attached to Ti6Al4V discs.

Use of a Silver Nylon Dressing Following Total Hip and Knee Arthroplasty Decreases the Postoperative Infection Rate

Introduction:

Prosthetic joint infection (PJI) is a potentially catastrophic complication of total joint replacement. Our purpose was to determine whether the use of a silver dressing reduces the incidence of superficial and deep PJI following primary total hip replacement and total knee replacement.

Methods:

A case-control study of primary total hip replacement and total knee replacement was performed to compare the incidence of superficial and deep PJI in patients who received a silver nylon dressing with patients who received a standard dressing.

Results:

The incidence of infection was significantly lower in the study group compared with the control group. There were no deep PJIs in the silver dressing group. Twelve patients (2.3%) in the control group developed PJI.

Discussion:

The use of a silver dressing significantly reduced the incidence of superficial and deep PJI following total joint replacement (P = 0.010). Given the financial impact of PJI, the application of silver dressings may result in considerable cost savings, and a formal cost-benefit analysis could be investigated.

Outcomes of Hip Arthroplasty After Failed Hip Arthroscopy: A Case-Control Study

BACKGROUND

Hip arthroscopy is increasingly being used in joint preservation surgery with clear benefits in the treatment of prearthritic conditions. A number of patients, however, will still go on to require subsequent hip arthroplasty, and at present, little evidence exists determining the impact that prior hip arthroscopy may have on the outcomes of a subsequent arthroplasty.

METHODS

Using prospectively collated data, we identified 35 patients who had a hip arthroplasty (22 total hip arthroplasties and 13 hip resurfacing arthroplasties) after prior ipsilateral hip arthroscopy (cases). Cases were matched for age, gender, and prosthesis type with 70 controls (patients who received a primary arthroplasty over the same period, without prior arthroscopy). Outcome measures included range of movement, implant survival, complications, and functional outcome (Oxford Hip Score and Harris Hip Score).

RESULTS

There was no demonstrable difference in improved range of motion after hip arthroplasty between the 2 groups, across any axis of movement (flexion, extension, internal/external rotation, abduction, and adduction; P = .07-.78). There was no significant difference in complication rate (P = .72). Overall 7-year implant survival was 85.9% (95% confidence interval [CI], 75-95.8). There was no difference in survival between cases (87.6%; 95% CI, 73.5-100) and controls (86.3%; 95% CI, 74.6%-98.0%; P = .2). Ten of the 11 revision arthroplasties performed were due to adverse reactions to metal debris in metal-on-metal hip resurfacing arthroplasty cases (P = .01). There was no difference in improvement of functional outcome postarthroplasty between groups (P = .48-.76).

CONCLUSION

This study demonstrates that hip arthroscopy does not adversely influence outcome of a subsequent hip arthroplasty.

Factors Associated with Choice and Success of One- Versus Two-Stage Revision Arthroplasty for Infected Hip and Knee Prostheses

BACKGROUND

Prosthetic joint infections (PJI) of hip and knee arthroplasties are becoming increasingly common with an aging population and an increasing demand for these procedures. Despite attempts at standardization, medical and surgical approaches vary widely among practitioners.

QUESTIONS/PURPOSES

We first sought to determine if there were specific factors associated with choice of one- versus two-stage revision. Then we investigated whether the type of revision approach influenced clinical treatment success. Finally, among two-stage revisions, we assessed if an antibiotic holiday prior to the second procedure affected clinical treatment success.

METHODS

We retrospectively reviewed patients who had revision surgery for infection of a hip or knee arthroplasty between January 1, 2000, and December 31, 2013, at the Sunnybrook Health Sciences Centre and the Holland Orthopedic and Arthritic Centre. PJI cases were identified using the Ontario Joint Replacement Registry. Infection was defined by gross intraoperative evidence of infection, positive intraoperative culture(s), and/or sinus tract prior to operation. The primary outcome was treatment failure at 1 year after revision surgery based on requirement for further surgery, ongoing infection, and/or continuous suppressive antibiotics.

RESULTS

Of 110 eligible patients identified, 35 patients had a one-stage and 75 patients had a two-stage revision. Choice of a one-stage approach was most influenced by particular surgeon preference and was more likely for hip revision versus knee revision (OR 3.39 (95%CI 1.85-6.23). There was no statistical difference in clinical treatment success rate between one-stage (33/35; 94.2% success) and two-stage revision (63/75; 84%; p = 0.13). Enterococcus spp. (21 versus 3%; p = 0.027) and Peptostreptococcus spp. (14 versus 1%; p = 0.042) were more common among clinical treatment failures than successes, with a trend towards the same for Staphylococcus aureus (29 versus 9%; p = 0.06). Additionally, treatment success was not influenced by whether the patient had an antibiotic holiday with a two-stage revision.

CONCLUSION

Our findings confirm the uncertainty of surgical strategy for treatment of PJI in hip and knee arthroplasty. Superiority of one- versus two-stage revision and the value of antibiotic-free periods prior to definitive revision remain unclear. Large prospective studies or randomized controlled trials are needed to inform best practice for treatment of these complex clinical problems.

Surgical site infections following instrumented stabilization of the spine

Background

Implant-associated infections are still a feared complication in the field of orthopedics. Bacteria attach to the implant surface and form so-called biofilm colonies that are often difficult to diagnose and treat. Since the majority of studies focus on prosthetic joint infections (PJIs) of the hip and knee, current treatment options (eg, antibiotic prophylaxis) of implant-associated infections have mostly been adapted according to these results.

Objective

The aim of this study was to evaluate patients with surgical site infections following instrumented stabilization of the spine with regard to detected bacteria species and the course of the disease.

Patients and methods

We performed a retrospective single-center analysis of implant-associated infections of the spine from 2010 to 2014. A total of 138 patients were included in the study. The following parameters were evaluated: C-reactive protein serum concentration, microbiological evaluation of tissue samples, the time course of the disease, indication for instrumented stabilization of the spine, localization of the infection, and the number of revision surgeries required until cessation of symptoms.

Results

Coagulase-negative Staphylococcus spp. were most commonly detected (n=69, 50%), followed by fecal bacteria (n=46, 33.3%). In 23.2% of cases, no bacteria were detected despite clinical suspicion of an infection. Most patients suffered from degenerative spine disorders (44.9%), followed by spinal fractures (23.9%), non-degenerative scoliosis (20.3%), and spinal tumors (10.1%). Surgical site infections occurred predominantly within 3 months (64.5%), late infections after 2 years were rare (4.3%), in particular when compared with PJIs. Most cases were successfully treated after 1 revision surgery (60.9%), but there were significant differences between bacteria species. Fecal bacteria were more difficult to treat and often required more than 1 revision surgery.

Conclusion

In summary, we were able to demonstrate significant differences between spinal implant-associated infections and PJIs. These aspects should be considered early on in the treatment of surgical site infections following instrumented stabilization of the spine.

In vitro activity of tedizolid and comparator agents against Gram-positive pathogens responsible for bone and joint infections

Tedizolid, a second-generation oxazolidinone that displays a potent activity against Gram-positive pathogens, could be an interesting option for the treatment of bone and joint infections (BJIs). The aim of the study was to determine minimal inhibitory concentration (MIC) of tedizolid against a collection of 359 clinical isolates involved in clinically-documented BJIs and to compare them to those of comparator agents used in Gram-positive infections. Of the 104 Staphylococcusaureus and 102 coagulase-negative staphylococci (CoNS) isolates, 99 and 92 % were categorized as susceptible to tedizolid, respectively (MIC25=0.12/0.25 µg ml^-1 and MIC90=0.25/0.5 µg ml^-1), regardless of their methicillin resistance. MIC50 and MIC90 for the 51 enterococci, the 50 Corynebacterium spp. and the 52 Propionibacterium spp. were either equal or inferior to 0.5 µg ml^-1. Altogether, tedizolid possessed a potent in vitro activity against most of the BJI Gram-positive pathogens with 95 % of them exhibiting a MIC ≤0.5 µg ml^-1.

Common Medical Comorbidities Correlated With Poor Outcomes in Hip Periprosthetic Infection

BACKGROUND

Periprosthetic infection has been linked to risk factors such as diabetes, obesity, and smoking among others. This study examined the relationship between common patient comorbidities and hip periprosthetic infection outcomes.

METHODS

We retrospectively reviewed the records of 149 culture-positive periprosthetic hip infections at our tertiary care center that underwent treatment between 2005 and 2015. Baseline characteristics and common comorbidities were analyzed with relation to rates of successfully treated infection, total surgeries for infection, and cumulative length of hospitalization using multivariate analysis.

RESULTS

Patients with coronary artery disease or anemia had significantly lower rate of successfully treated infection. Patients with anemia or chronic pulmonary disease underwent significantly more surgery, and patients with chronic pulmonary disease, psychiatric disease, anemia, or diabetes spent significantly longer time in hospital.

CONCLUSION

Potentially modifiable cardiovascular, respiratory, and psychiatric diseases were associated with a decreased rate of successfully treated infection, more surgery, and longer hospitalization in treatment for hip periprosthetic infection in multivariate analysis.

Using Engineered Bacteria to Characterize Infection Dynamics and Antibiotic Effects In Vivo

Synthetic biology has focused on engineering microbes to synthesize useful products or to serve as living diagnostics and therapeutics. Here we utilize a host-derived Escherichia coli strain engineered with a genetic toggle switch as a research tool to examine in vivo replicative states in a mouse model of chronic infection, and to compare in vivo and in vitro bacterial behavior. In contrast to the effect of antibiotics in vitro, we find that the fraction of actively dividing bacteria remains relatively high throughout the course of a chronic infection in vivo and increases in response to antibiotics. Moreover, the presence of non-dividing bacteria in vivo does not necessarily lead to an antibiotic-tolerant infection, in contrast to expectations from in vitro experiments. These results demonstrate the utility of engineered bacteria for querying pathogen behavior in vivo, and the importance of validating in vitro studies of antibiotic effects with in vivo models.

Accuracy of different diagnostic tests for early, delayed and late prosthetic joint infection

BACKGROUND

A combination of laboratory, histopathological and microbiological tests for diagnosis of prosthetic joint infection (PJI) have been strongly recommended. This study aims to characterize the accuracy of individual or group tests, such as culture of sonicate fluid, synovial fluid and peri-implant tissue, C-reactive protein (CRP) and histopathology for detection of early, delayed and late PJI.

METHODS

A prospective study of patients undergoing hip or knee arthroplasty from February 2009 to February 2014 was performed in a Spanish tertiary health care hospital. The diagnostic accuracy of the different methods was evaluated constructing receiver-operating-characteristic (ROC) curve areas.

RESULTS

One hundred thirty consecutive patients were included: 18 (13.8%) early PJI, 35 (27%) delayed PJI and 77 (59.2%) late PJI. For individual parameters, the area under the ROC curve for peri-implant tissue culture was larger for early (0.917) than for delayed (0.829) and late PJI (0.778), p = 0.033. There was a significantly larger difference for ROC area in the synovial fluid culture for delayed (0.803) than for early (0.781) and late infections (0.679), p = 0.039. The comparison of the areas under the ROC curves for the two microbiological tests showed that sonicate fluid was significantly different from peri-implant tissue in delayed (0.951 vs 0.829, p = 0.005) and late PJI (0.901 vs 0.778, p = 0.000). The conjunction of preoperative parameters, synovial fluid culture and CRP, improved the accuracy for late PJI (p = 0.01). The conjunction of histopathology and sonicate fluid culture increased the area under ROC curve of sonication in early (0.917 vs 1.000); p = 0.06 and late cases (0.901 vs 0.999); p < 0.001.

CONCLUSION

For early PJI, sonicate fluid and peri-implant tissue cultures achieve the same best sensitivity. For delayed and late PJI, sonicate fluid culture is the most sensitive individual diagnostic method. By combining histopathology and peri-implant tissue, all early, 97% of delayed and 94.8% of late cases are diagnosed. The conjunction of histopathology and sonicate fluid culture yields a sensitivity of 100% for all types of infection.

Use of Common Inflammatory Markers in the Long-Term Screening of Total Hip Arthroprosthesis Infections: Our Experience

Orthopedic implants have become essential components of modern medicine. The risk of infection of total hip arthroplasty (THA) is 1.5%-2%. Are the C-reactive protein (CRP), the erythrocyte sedimentation rate (ESR), and procalcitonin (PCT) good markers for THA infection screenings? From February 2009 to December 2012 at our Department of Orthopedics and Traumatology, 1248 patients were treated with THA. No prosthesis was cemented. All patients received antibiotic prophylaxis. All patients were discharged approximately 7.4 days after surgery with this clinical and radiographic follow-up program at 15 days and 1, 3, 6, 12, 24, and 36 months after surgery. Blood samples to determine ESR, CRP, and PCT values were taken at 1 hour before surgery and 15 days and 1, 3, 6, 12, 24, and 36 months after surgery. During follow-ups there were 22 cases of THA infections; according the Widmer classification, infections are hematogenous ones in 16 cases, late chronic ones in 5 cases, and early postoperative ones in 1 case. In all cases the three markers were considered positive; in 6 cases there were no radiological signs of septic loosening. ESR, CRP, and PCT proved to have a greater diagnostic accuracy than X-rays in predicting late chronic and early postoperative infections. These markers are valuable support for the surgeon in monitoring the prosthetic implant lifespan.

Gonococcal Prosthetic Joint Infection

Neisseria gonorrhoea is a common sexually transmitted infection worldwide. Disseminated gonococcal infection is an infrequent presentation and rarely can be associated with septic arthritis. Incidence of this infection is rising, both internationally and in older age groups. We present the first documented case of N. gonorrhoea prosthetic joint infection which was successfully treated with laparoscopic debridement and antimicrobial therapy.

Role of Nuclear Medicine for Diagnosing Infection of Recently Implanted Lower Extremity Arthroplasties

Infection is an infrequent complication of lower extremity prosthetic joint surgery. Approximately one-third develop within 3 months (early), another third within 1 year (delayed), and the remainder more than 1 year (late) after surgery. Diagnosing prosthetic joint infection, especially in the early postoperative period during the first year, is challenging. Pain is almost always present. The presence of fever is variable, ranging from less than 5% to more than 40% of patients. Leukocytosis is a poor predictor of infection. After primary uncomplicated arthroplasty, the C-reactive protein remains elevated for up to 3 weeks. The erythrocyte sedimentation rate can remain elevated for up to 1 year. Although joint aspiration with culture, the definitive preoperative diagnostic procedure, is specific, its sensitivity is variable. Plain radiographs lack sensitivity and specificity. Radionuclide studies are useful for evaluating painful joint replacements, but data on their utility during the early postoperative period are limited. During the first year after arthroplasty insertion, the bone scan can exclude infection. It is a good "rule-out" test, but it is not reliable for "ruling in" infection. Gallium-67 accumulates in normally healing surgical incisions and in aseptic inflammation. With an accuracy of 60%-80% for diagnosing prosthetic joint infection, there is little role for this radiopharmaceutical for evaluating prosthetic joints, regardless of age. Although data about diagnosing prosthetic joint infection with ¹⁸F-FDG in the early postoperative period are lacking, uptake of this radiopharmaceutical in a variety of postoperative settings for variable time periods is well known. Furthermore, its utility for diagnosing prosthetic joint infection in general, after nearly 2 decades of investigation, remains to be established. Indium-111-labeled leukocytes do not accumulate in normally healing surgical wounds, and in combination with marrow imaging, the test is about 90% accurate for diagnosing prosthetic joint infection. Preliminary data indicate a comparable accuracy in the early postoperative period.

Q fever prosthetic joint infection

Coxiella burnetii is the causative pathogen of the zoonotic infection Q fever. Most patients with Q fever experience a non-specific febrile illness, hepatitis or pneumonia. Q fever has recently been described as a cause of prosthetic joint septic arthritis, but remains very uncommonly reported. We present a case of Q fever prosthetic joint septic arthritis that has responded to a combination of two-stage surgical exchange and prolonged medical treatment with doxycycline and hydroxychloroquine.

Staged Reimplantation of a Total Hip Prosthesis After Co-infection with Candida tropicalis and Staphylococcus haemolyticus: A Case Report

Fungal prosthetic joint infection is a rare complication in total joint arthroplasty. There are no established guidelines for management of these infections. We present a case of a 53-year-old male with a hip joint prosthesis co-infected with Candida tropicalis and Staphylococcus haemolyticus. A two-stage exchange arthroplasty was performed. The patient underwent implant removal, debridement, irrigation with saline solution and application of cement spacer impregnated with vancomycin followed by aggressive antimicrobial treatment in first stage. Complete eradication of infection was demonstrated by negative culture of sonicated cement spacer fluid and negative 16S rRNA and 18S rRNA gene PCR of sonicate fluid, synovial fluid and periprosthetic tissue samples. He underwent second-stage revision hip arthroplasty after 9 months of the first stage. At the latest follow-up, there was no evidence of recurrence of infection. This case illustrates the utility of sonication of biomaterials and molecular techniques for microbiological confirmation of absence of infection in staged surgeries which is required for a successful outcome.

Affinity interactions drive post-implantation drug filling, even in the presence of bacterial biofilm

Current post-operative standard of care for surgical procedures, including device implantations, dictates prophylactic antimicrobial therapy, but a percentage of patients still develop infections. Systemic antimicrobial therapy needed to treat such infections can lead to downstream tissue toxicities and generate drug-resistant bacteria. To overcome issues associated with systemic drug administration, a polymer incorporating specific drug affinity has been developed with the potential to be filled or refilled with antimicrobials, post-implantation, even in the presence of bacterial biofilm. This polymer can be used as an implant coating or stand-alone drug delivery device, and can be translated to a variety of applications, such as implanted or indwelling medical devices, and/or surgical site infections. The filling of empty affinity-based drug delivery polymer was analyzed in an in vitro filling/refilling model mimicking post-implantation tissue conditions. Filling in the absence of bacteria was compared to filling in the presence of bacterial biofilms of varying maturity to demonstrate proof-of-concept necessary prior to in vivo experiments. Antibiotic filling into biofilm-coated affinity polymers was comparable to drug filling seen in same affinity polymers without biofilm demonstrating that affinity polymers retain ability to fill with antibiotic even in the presence of biofilm. Additionally, post-implantation filled antibiotics showed sustained bactericidal activity in a zone of inhibition assay demonstrating post-implantation capacity to deliver filled antibiotics in a timeframe necessary to eradicate bacteria in biofilms. This work shows affinity polymers can fill high levels of antibiotics post-implantation independent of biofilm presence potentially enabling device rescue, rather than removal, in case of infection.

STATEMENT OF SIGNIFICANCE

Post-operative prophylactic antimicrobial therapy greatly reduces risk of infection, such as on biomedical implants, but does not totally eliminate infections, and the healthcare cost of these remaining infections remains a major concern. Systemic antimicrobial therapy to treat these infections can lead to tissue toxicity and drug-resistant bacteria. In order to treat only those patients who have developed infections, a customizable antimicrobial delivery system made of cyclodextrin-based affinity polymer has been developed that is capable of filling post-implantation and delivering the filled antibiotic in a sustained manner even when the delivery device covered in bacterial biofilm. These observations have the potential to be translated to a wide variety of applications, such as implanted or indwelling medical devices, and/or surgical site infections.

α-Defensin point-of-care test for diagnosis of prosthetic joint infections: neglected role of laboratory and clinical pathologists

Periprosthetic joint infection (PJI) is a serious complication that may occur after native joint replacement leading to a severe health and economic burden. Currently, due to several confounding factors, PJI is difficult to diagnose. Today, a multidisciplinary approach is indispensable to correctly define a periprosthetic joint infection; indeed, tissue histology, microbiology cultures and clinical findings are used together to achieve this goal. Analysis of α-defensin is commonly used for PJI diagnosis, as it allows the rapid detection of α-defensin present in the synovial fluid following a microbial infection. Currently, a point-of-care testing (POCT) assay able to detect the presence of human α-defensins 1–3 in synovial fluid of patients is aimed directly at orthopedic surgeons. However, many orthopedic surgeons lack experience and training in quality laboratory practices, often failing to appreciate the significance of quality control and proper documentation when using POCT assays. To guarantee the highest quality diagnostic services, the α-defensin test should be used together with other biochemical and microbiological criteria commonly used for PJI diagnosis. Additionally, the close cooperation and communication between laboratory, pathologists and physicians is of fundamental importance in the correct diagnosis of PJI.

Laboratory Workflow Analysis of Culture of Periprosthetic Tissues in Blood Culture Bottles

Culture of periprosthetic tissue specimens in blood culture bottles is more sensitive than conventional techniques, but the impact on laboratory workflow has yet to be addressed. Herein, we examined the impact of culture of periprosthetic tissues in blood culture bottles on laboratory workflow and cost. The workflow was process mapped, decision tree models were constructed using probabilities of positive and negative cultures drawn from our published study (T. N. Peel, B. L. Dylla, J. G. Hughes, D. T. Lynch, K. E. Greenwood-Quaintance, A. C. Cheng, J. N. Mandrekar, and R. Patel, mBio 7:e01776-15, 2016, https://doi.org/10.1128/mBio.01776-15), and the processing times and resource costs from the laboratory staff time viewpoint were used to compare periprosthetic tissues culture processes using conventional techniques with culture in blood culture bottles. Sensitivity analysis was performed using various rates of positive cultures. Annualized labor savings were estimated based on salary costs from the U.S. Labor Bureau for Laboratory staff. The model demonstrated a 60.1% reduction in mean total staff time with the adoption of tissue inoculation into blood culture bottles compared to conventional techniques (mean ± standard deviation, 30.7 ± 27.6 versus 77.0 ± 35.3 h per month, respectively; P < 0.001). The estimated annualized labor cost savings of culture using blood culture bottles was $10,876.83 (±$337.16). Sensitivity analysis was performed using various rates of culture positivity (5 to 50%). Culture in blood culture bottles was cost-effective, based on the estimated labor cost savings of $2,132.71 for each percent increase in test accuracy. In conclusion, culture of periprosthetic tissue in blood culture bottles is not only more accurate than but is also cost-saving compared to conventional culture methods.

Infections after shoulder arthroplasty are correlated with higher anesthetic risk score: a case-control study in Brazil

Purposes

Shoulder arthroplasty (SA) has been performed by many years for the treatment of several conditions, including osteoarthritis and proximal humeral fractures following trauma. Surgical site infection (SSI) following Shoulder arthroplasty remains a challenge, contributing to increased morbidity and costs. Identification of risk factors may help implementing adequate strategies to prevent infection. We aimed to identify pre- and intra-operative risk factors associated with deep infections after Shoulder arthroplasty.

Methods

An unmatched case-control study was conducted to describe the prevalence, clinical and microbiological findings, and to evaluate patient and surgical risk factors for prosthetic shoulder infection (PSI), among 158 patients who underwent SA due to any reason, at a tertiary public university institution. Risk factors for PSI was assessed by uni- and multivariate analyses using multiple logistic regression.

Results

168 SA from 158 patients were analyzed, with an overall infection rate of 9.5% (16/168 cases). Subjects undergoing SA with American Society of Anesthesiologists (ASA) grade III or higher (odds ratio [OR] = 5.30, 95% confidence interval [CI] = 1.58–17.79, p < 0.013) and presenting local hematoma after surgery (odds ratio [OR] = 7.10, 95% confidence interval [CI] = 1.09–46.09, p = 0.04) had higher risk for PSI on univariate analysis. However, only ASA score grade III or higher remained significant on multivariate analysis (OR = 4.74, 95% CI = 1.33–16.92, p = 0.016). Gram-positive cocci and Gram-negative bacilli were equally isolated in 50% of cases; however, the most commonly detected bacterium was Pseudomonas aeruginosa (18.7%).

Conclusion

This study provides evidence suggesting that patient-related known factors such as higher ASA score predisposes to shoulder arthroplasty-associated infection. Furthermore, unusual pathogens associated with PSI were identified.

Oral Therapy, Microbiological Findings, and Comorbidity Influence the Outcome of Prosthetic Joint Infections Undergoing 2-Stage Exchange

BACKGROUND

The aim of the present study was to investigate potential predictive factors of an unfavorable outcome in patients with prosthetic joint infection (PJI) undergoing 2-stage exchange.

METHODS

Patients with PJI undergoing 2-stage exchange and observed over a 5-year period (2009-2013) were included. Cure was defined by the disappearance of infection after a 96-week follow-up period. Statistical analysis was performed using the Mann-Whitney U test, the Fisher exact test, and the multivariate analysis.

RESULTS

One-hundred twenty-two patients with PJI were included (median age, 69 years [range, 36-80 years]; 48% males, 47 hip PJI, and 75 knee PJI). Known comorbidities related to an increased risk of infection were reported in 43 patients (35%). Microbiological definition was obtained in 101 (83%) patients, and Staphylococcus aureus was isolated in 44 (36%) patients. Coagulase-negative staphylococci were isolated in 41 (34%) patients. A favorable outcome was obtained in 102 of 122 patients (84%). After univariate analysis, bacterial growth from operative specimens (P = .007), growth of Gram-positive bacteria (P < .001), use of oral therapy (P = .01), and absence of known comorbidities (P = .02) were associated with favorable outcome. Administration of rifampin (P = .99) and results of blood analysis were not predictive of outcome. After multivariate analysis was applied, infection sustained by Gram-positive bacteria, administration of oral antibiotics, and absence of known comorbidities frequently resulted in favorable outcome.

CONCLUSION

A favorable outcome in patients with PJI undergoing 2-stage procedure was associated with an infection sustained by Gram-positive bacteria, absence of known comorbidities, and administration of oral therapy. Therefore, failure rate can be reduced with appropriate treatment choices.

Increased Resistance of Skin Flora to Antimicrobial Prophylaxis in Patients Undergoing Hip Revision Arthroplasty

BACKGROUND/AIM

Prosthetic joint infection (PJI) remains a major complication after total joint replacement and is the primary indication for revision arthroplasty. Specifically, coagulase-negative Staphylococci (CNS) can cause low-grade infections. Despite the use of cephalosporin-based antimicrobial prophylaxis (AMP) and antiseptic treatment at the surgical site, evidence suggests that a significant number of cases of dermal CNS results in low-grade PJI. Thus, this study examined the bacterial colonization and resistance patterns at the surgical site. We hypothesized that the bacteria developed resistance to antibiotics that are frequently used in primary and revision total hip arthroplasty (THA) procedures.

PATIENTS AND METHODS

Ninety patients, including 63 primary and 27 revision THA patients, were enrolled in this study. For each patient, a single swab of the skin at the surgical site was subjected to clinical microbiology to assess bacterial colonization. Furthermore, resistance to a sentinel panel of antibiotics (benzylpenicillin, erythromycin, tetracycline, oxacillin, fusidic acid, clindamycin, gentamicin, levofloxacin/moxifloxacin, rifampicin, linezolid and vancomycin) was tested.

RESULTS

In 96.7% of the patients, at least one bacterial strain was identified at the surgical site, with CNS strains comprising 93.1% of the total. The sentinel panel showed that 30.7% of the CNS strains exhibited maximal resistance to oxacillin, a commonly used cephalosporin. Additionally, oxacillin resistance increased 1.9-fold (p=0.042) between primary and revision THA. Notably, 8.1% of the CNS stains found on patients undergoing primary THA were resistant to gentamicin, an aminoglycoside, and this rate increased 4.7-fold (p=0.001) for patients undergoing revision THA.

CONCLUSION

CNS strains have significant resistance to standard AMP, particularly in individuals undergoing revision THA.

Risk of surgical site infection, acute kidney injury, and Clostridium difficile infection following antibiotic prophylaxis with vancomycin plus a beta-lactam versus either drug alone: A national propensity-score-adjusted retrospective cohort study

BACKGROUND

The optimal regimen for perioperative antimicrobial prophylaxis is controversial. Use of combination prophylaxis with a beta-lactam plus vancomycin is increasing; however, the relative risks and benefits associated with this strategy are unknown. Thus, we sought to compare postoperative outcomes following administration of 2 antimicrobials versus a single agent for the prevention of surgical site infections (SSIs). Potential harms associated with combination regimens, including acute kidney injury (AKI) and Clostridium difficile infection (CDI), were also considered.

METHODS AND FINDINGS

Using a multicenter, national Veterans Affairs (VA) cohort, all patients who underwent cardiac, orthopedic joint replacement, vascular, colorectal, and hysterectomy procedures during the period from 1 October 2008 to 30 September 2013 and who received planned manual review of perioperative antimicrobial prophylaxis regimen and manual review for the 30-day incidence of SSI were included. Using a propensity-adjusted log-binomial regression model stratified by type of surgical procedure, the association between receipt of 2 antimicrobials (vancomycin plus a beta-lactam) versus either single agent alone (vancomycin or a beta-lactam) and SSI was evaluated. Measures of association were adjusted for age, diabetes, smoking, American Society of Anesthesiologists score, preoperative methicillin-resistant Staphylococcus aureus (MRSA) status, and receipt of mupirocin. The 7-day incidence of postoperative AKI and 90-day incidence of CDI were also measured. In all, 70,101 procedures (52,504 beta-lactam only, 5,089 vancomycin only, and 12,508 combination) with 2,466 (3.5%) SSIs from 109 medical centers were included. Among cardiac surgery patients, combination prophylaxis was associated with a lower incidence of SSI (66/6,953, 0.95%) than single-agent prophylaxis (190/12,834, 1.48%; crude risk ratio [RR] 0.64, 95% CI 0.49, 0.85; adjusted RR 0.61, 95% CI 0.46, 0.83). After adjusting for SSI risk, no association between receipt of combination prophylaxis and SSI was found for the other types of surgeries evaluated, including orthopedic joint replacement procedures. In MRSA-colonized patients undergoing cardiac surgery, SSI occurred in 8/346 (2.3%) patients who received combination prophylaxis versus 4/100 (4.0%) patients who received vancomycin alone (crude RR 0.58, 95% CI 0.18, 1.88). Among MRSA-negative and -unknown cardiac surgery patients, SSIs occurred in 58/6,607 (0.9%) patients receiving combination prophylaxis versus 146/10,215 (1.4%) patients who received a beta-lactam alone (crude RR 0.61, 95% CI 0.45, 0.83). Based on these associations, the number needed to treat to prevent 1 SSI in MRSA-colonized patients is estimated to be 53, compared to 176 in non-MRSA patients. CDI incidence was similar in both exposure groups. Across all types of surgical procedures, risk of AKI was increased in the combination antimicrobial prophylaxis group (2,971/12,508 [23.8%] receiving combination versus 1,058/5,089 [20.8%] receiving vancomycin alone versus 7,314/52,504 [13.9%] receiving beta-lactam alone). We found a significant association between absolute risk of AKI and receipt of combination regimens across all types of procedures. If the observed association is causal, the number needed to harm for severe AKI following cardiac surgery would be 167. The major limitation of our investigation is that it is an observational study in a predominantly male population, which may limit generalizability and lead to unmeasured confounding.

CONCLUSIONS

There are benefits but also unintended consequences of antimicrobial and infection prevention strategies aimed at "getting to zero" healthcare-associated infections. In our study, combination prophylaxis was associated with both benefits (reduction in SSIs following cardiac surgical procedures) and harms (increase in postoperative AKI). In cardiac surgery patients, the difference in risk-benefit profile by MRSA status suggests that MRSA-screening-directed prophylaxis may optimize benefits while minimizing harms in this selected population. More information about long-term outcomes and patient and societal preferences regarding risk of SSI versus risk of AKI is needed to improve clinical decision-making.

Ica-status of clinical Staphylococcus epidermidis strains affects adhesion and aggregation: a thermodynamic analysis

Staphylococcus epidermidis is a major nosocomial pathogen associated with infections of indwelling medical devices. One important virulence factor of these organisms is their ability to adhere to devices and form biofilms. In this study, we evaluated the effect of the ica operon on cell surface hydrophobicity, thermodynamics of adhesion, and biofilm formation for seven S. epidermidis strains. The surface free energy parameters of the bacterial cell surface and the substratum were determined by contact angle measurement. Biofilm formation was assayed using crystal violet staining. Results showed that ica-positive strains demonstrated a higher hydrophobic characteristic than ica-negative strains, suggesting that the ica-operon seems to determine the cell surface hydrophobicity of S. epidermidis. Interaction of ica-positive strains with a tissue-culture treated polystyrene surface was energetically favourable (ΔG^Tot < 0), in contrast to ica-negative strains (ΔG^Tot > 0). The interfacial free energy of aggregation of S. epidermidis was lower for ica-positive than for ica-negative strains. Our study suggests that, in addition to biofilm formation, adhesion and aggregation of clinical S. epidermidis is stimulated in ica-positive strains by influencing the thermodynamics of interaction.

Acute periprosthetic knee infection: is there still a role for DAIR?

BACKGROUND AND AIM OF THE WORK

Periprosthetic knee infection is a rare complication associated with prosthetic failure; incidence change from 0,4-2% of primary total knee replacement and 5.6% in revisions. Indications for debridment, antibiotics and implant retention (DAIR) are early acute infections or acute delayed infection. Aim of the work is to check if this technique is still a successful in early infections.

METHODS

We have analyzed recent literature data on DAIR and all DAIR procedures in our clinic in the last 10 years, the mean time between onset of symptoms and surgery, the mean antibiotic therapy duration and results we have obtained. We evaluate the diagnostic process and different treatments in early knee periprosthetic infections, especially the DAIR approach.

RESULTS

If correct indications are followed, DAIR has a success rate in 31-100% of the cases; if it is applied in late chronic infection the success rate is 28-62%. In our experience DAIR has an 80% success rate: in 20 patients treated with DAIR we had 4 failures.

CONCLUSIONS

DAIR can be considered a successful treatment, but it depends from individual patient factors, from the microorganisms involved, from the duration of antibiotic therapy and from correct choice in timing and in execution of DAIR by the orthopedic surgeon.

Two-stage revision after total knee arthroplasty

BACKGROUND AND AIM OF THE WORK

Periprosthetic knee infection is a complication associated with prosthetic failure; incidence change from 0,4-2% of primary total knee replacement and 5,6% in revisions; incidence is increasing over the years. Two-stage revision is the technique used in chronic infection. Aim of the work is to check success rate in our data. Methods. We analyzed retrospectively data of patients who undergone two stage revision surgery between 01/01/2010 to 31/12/2015. We made a clinical and radiological control after 1, 3, 6, 12, 24 months and we evaluate the outcome in December 2016. Results. Between 2010 and 2015 we treated 45 patients with two-stage revision. Mean follow-up was 3,4 years. Success rate is 89,9%. We had failure in 5 patients: everyone had knee surgery before first knee arthroplasty and Charlson Comorbidity Score was greater then 4 in 4 cases. Conclusions. Two stage revision can be considered a successful treatment in chronic periprosthetic knee infection. It has an optimal success rate, but it has some disadvantages as joint stiffness and pain in the interval between stages. This is a technique with two major surgery procedure with associated morbidity, discomfort, cost and prolonged stay in hospital.

Specific Infectious Organisms Associated With Poor Outcomes in Treatment for Hip Periprosthetic Infection

BACKGROUND

Periprosthetic hip infection treatment remains a significant challenge for orthopedics. Some studies have suggested that methicillin resistance and gram-negative organism type are associated with increased treatment failure. The aim of this research is to determine if specific organisms were associated with poor outcomes in treatment for hip periprosthetic infection.

METHODS

Records were reviewed of all patients between 2005 and 2015 who underwent treatment for infected partial or total hip arthroplasty. Characteristics of each patient's treatment course were determined including baseline characteristics, infecting organism(s), infection status at final follow-up, surgeries for infection, and time in hospital. Baseline characteristics and organisms that were associated with clinical outcomes in univariate analysis were incorporated into multivariable outcomes models.

RESULTS

When compared with patients infected with other organism(s), patients infected with the following organisms had significantly decreased infection-free rates: Pseudomonas, methicillin-resistant Staphylococcus aureus (MRSA), and Proteus. Infection with certain organisms was associated with 1.13-2.58 additional surgeries: methicillin-sensitive S aureus, coagulase-negative Staphylococcus, MRSA, Pseudomonas, Peptostreptococcus, Klebsiella, Candida, diphtheroids, Propionibacterium acnes, and Proteus species. Specific organisms were associated with 8.56-24.54 additional days in hospital for infection: methicillin-sensitive S aureus, coagulase-negative Staphylococcus, Proteus, MRSA, Enterococcus, Pseudomonas, Klebsiella, beta-hemolytic Streptococcus, and diphtheroids. Higher comorbidity score was also associated with greater length of hospitalization.

CONCLUSION

MRSA, Pseudomonas, and Proteus were associated with all 3 outcomes of lower infection-free rate, more surgery, and more time in hospital in treatment for hip periprosthetic infection. Organism-specific outcome information may help individualize patient-physician discussions about the expected course of treatment for hip periprosthetic infection.

Assessment of the automated multiplex-PCR Unyvero i60 ITI® cartridge system to diagnose prosthetic joint infection: a multicentre study

OBJECTIVES

Prosthetic joint infections (PJI) are responsible for significant morbidity and mortality and their number continues to rise. Their management remains complex, especially the microbiological diagnosis. Besides 'homemade' tests developed by several teams, new molecular biology methods are now available with different analytical performance and usability.

METHODS

We studied the performances of one of these tests: ITI^® multiplex PCR (mPCR) by the Curetis^® company and compared it to either 'optimized' culture or 16S rRNA PCR. We performed a retrospective multicentre study to assess the contributions of mPCR in the diagnosis of PJI. We randomly selected 484 intraoperative specimens among 1252 of various types (biopsy, bone, tissue around the prosthesis, synovial fluid) from 251 patients in seven different hospitals. Each sample was treated according to the recommendations of the manufacturer.

RESULTS

In all, 154 out of 164 (93.9%) samples negative in culture were negative with the mPCR. Among the 276 positive samples in culture, 251 (90.9%) were monomicrobial, of which 119 (47.4%) were positive with the mPCR, and 25 (9.1%) were polymicrobial, of which 12 (48%) were positive with the mPCR. The concordance rate of mPCR with culture was 58.1% (53.6%-62.7%) and the concordance rate with 16S rRNA PCR was 70.1% (65.5%-74.6%).

CONCLUSION

This new standardized molecular test showed a lack of detection when the bacterial inoculum was low (number of positive media per sample and number of colonies per media) but can be useful when patients have received antibiotic therapy previously.

Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the "race for the surface" theory

Objectives

Implant-related infection is one of the most devastating complications in orthopaedic surgery. Many surface and/or material modifications have been developed in order to minimise this problem; however, most of the in vitro studies did not evaluate bacterial adhesion in the presence of eukaryotic cells, as stated by the ‘race for the surface’ theory. Moreover, the adherence of numerous clinical strains with different initial concentrations has not been studied.

Methods

We describe a method for the study of bacterial adherence in the presence of preosteoblastic cells. For this purpose we mixed different concentrations of bacterial cells from collection and clinical strains of staphylococci isolated from implant-related infections with preosteoblastic cells, and analysed the minimal concentration of bacteria able to colonise the surface of the material with image analysis.

Results

Our results show that clinical strains adhere to the material surface at lower concentrations than collection strains. A destructive effect of bacteria on preosteoblastic cells was also detected, especially with higher concentrations of bacteria.

Conclusions

The method described herein can be used to evaluate the effect of surface modifications on bacterial adherence more accurately than conventional monoculture studies. Clinical strains behave differently than collection strains with respect to bacterial adherence.

Cite this article: M. Martinez-Perez, C. Perez-Jorge, D. Lozano, S. Portal-Nuñez, R. Perez-Tanoira, A. Conde, M. A. Arenas, J. M. Hernandez-Lopez, J. J. de Damborenea, E. Gomez-Barrena, P. Esbrit, J. Esteban. Evaluation of bacterial adherence of clinical isolates of Staphylococcus sp. using a competitive model: An in vitro approach to the “race for the surface” theory. Bone Joint Res 2017;6:315–322. DOI: 10.1302/2046-3758.65.BJR-2016-0226.R2.

Hyperbaric Oxygen Therapy is Ineffective as an Adjuvant to Daptomycin with Rifampicin Treatment in a Murine Model of Staphylococcus aureus in Implant-Associated Osteomyelitis

Implant-associated infections caused by bacterial biofilms are difficult to treat. Surgical intervention is often necessary to cure the patient, as the antibiotic recalcitrance of biofilms renders them untreatable with conventional antibiotics. Intermittent hyperbaric oxygen treatment (HBOT) has been proposed as an adjuvant to conventional antibiotic treatment and it has been speculated that combining HBOT with antibiotics could improve treatment outcomes for biofilm infections. In this study we addressed whether HBOT could improve treatment outcomes of daptomycin and rifampicin combination therapy. The effect of HBOT on the treatment outcomes of daptomycin and rifampicin against implant-associated osteomyelitis was quantified in a murine model. In total, 80 mice were randomized into two groups receiving antibiotics, either alone or in combination with daily intermittent HBOT (304 kPa for 60 min) following injection of antibiotics. Treatment was initiated 11 days after animals were infected with Staphylococcus aureus and treatment duration was 14 days. We found that HBOT did not improve the cure rate and did not reduce the bacterial load on the implant surface or in the surrounding tissue. Cure rates of daptomycin + rifampicin were 40% in infected tibias and 75% for implants while cure rates for HBOT-daptomycin + rifampicin were 50% and 85%, respectively, which were not significantly higher (Fisher’s exact test). While it is encouraging that the combination of daptomycin and rifampicin is very effective, our study demonstrates that this efficacy cannot be improved by adjuvant HBOT.

Microbiological diagnosis of device-related biofilm infections

Medical device-related infections cause undue patient distress, increased morbidity and mortality and pose a huge financial burden on healthcare services. The pathogens are frequently distributed heterogeneously in biofilms, which can persist without being effectively cleared by host immune defenses and antibiotic therapy. At present, there is no 'gold standard' available to reveal the presence of device-related biofilm infections. However, adequate sample collection and logistics, standardised diagnostic methods, and interpretation of results by experienced personnel are important steps in efficient diagnosis and treatment of these infections. The focus of this mini review is on prosthethic joint and cardiovascular implantable device infections, which exemplify permanent devices that are placed in a sterile body site. These device-related infections represent some of the most challenging in terms of both diagnosis and treatment.

Prevention of Propionibacterium acnes biofilm formation in prosthetic infections in vitro

BACKGROUND

The role of Propionibacterium acnes in shoulder arthroplasty and broadly in orthopedic prosthetic infections has historically been underestimated, with biofilm formation identified as a key virulence factor attributed to invasive isolates. With an often indolent clinical course, P acnes infection can be difficult to detect and treat. This study investigates absorbable cements loaded with a broad-spectrum antibiotic combination as an effective preventive strategy to combat P acnes biofilms.

METHODS

P acnes biofilm formation on an unloaded synthetic calcium sulfate (CaSO₄) bone void filler cement bead was evaluated by scanning electron microscopy over a period of 14 days. Beads loaded with tobramycin alone or vancomycin alone (as comparative controls) and beads loaded with a vancomycin-tobramycin dual treatment were assessed for their ability to eradicate planktonic P acnes, prevent biofilm formation, and eradicate preformed biofilms using a combination of viable-cell counts, confocal microscopy, and scanning electron microscopy.

RESULTS

P acnes surface colonization and biofilm formation on unloaded CaSO₄ beads was slow. Beads loaded with antibiotics were able to kill planktonic cultures of 10⁶ colony-forming units/mL, prevent bacterial colonization, and significantly reduce biofilm formation over periods of weeks. Complete eradication of established biofilms was achieved with a contact time of 1 week.

CONCLUSIONS

This study demonstrates that antibiotic-loaded CaSO₄ beads may represent an effective antibacterial and antibiofilm strategy to combat prosthetic infections in which P acnes is involved.

Management of Prosthetic Joint Infection

Although uncommon, prosthetic joint infection is a devastating complication. This challenging condition requires a coordinated management approach to achieve good patient outcomes. This review details the general principles to consider when managing patients with prosthetic joint infection. The different medical/surgical treatment strategies and how to appropriately select a strategy are discussed. The data to support each strategy are presented, along with discussion of antimicrobial strategies in specific situations.

Impact of Contaminating DNA in Whole-Genome Amplification Kits Used for Metagenomic Shotgun Sequencing for Infection Diagnosis

Whole-genome amplification (WGA) is a useful tool for amplification of very small quantities of DNA for many uses, including metagenomic shotgun sequencing for infection diagnosis. Depending on the application, background DNA from WGA kits can be problematic. Three WGA kits were tested for their utility in a metagenomics approach to identify the pathogens in sonicate fluid comprised of biofilms and other materials dislodged from the surfaces of explanted prosthetic joints using sonication. The Illustra V2 Genomiphi, Illustra single cell Genomiphi, and Qiagen REPLI-g single cell kits were used to test identical sonicate fluid samples. Variations in the number of background reads, the genera identified in the background, and the number of reads from known pathogens known to be present in the samples were observed between kits. These results were then compared to those obtained with a library preparation without prior WGA using an NEBNext Ultra II paired-end kit, which requires a very small amount of input DNA. This approach also resulted in the presence of contaminant bacterial DNA and yielded fewer reads from the known pathogens. These findings highlight the impact that WGA kit selection can have on metagenomic analysis of low-biomass samples and the importance of the careful selection and consideration of the implications of using these tools.

Clinical and Microbiological Characteristics of Bacteroides Prosthetic Joint Infections

Clinical and microbiological characteristics of patients with Bacteroides prosthetic joint infection (PJI) have not been well described in the literature. The aim of this retrospective cohort study was to assess the outcome of patients with Bacteroides PJI and to review risk factors associated with failure of therapy. Between 1/1969 and 12/2012, 20 episodes of Bacteroides PJI in 17 patients were identified at our institution. The mean age of the patients in this cohort at the time of diagnosis was 55.6 years; 59% (n=10) had knee involvement. Twenty four percent (n=4) had diabetes mellitus, and 24% had a history of either gastrointestinal (GI) or genitourinary (GU) pathology prior to the diagnosis of PJI. Thirty five percent (n=6) were immunosuppressed. The initial medical/surgical strategy was resection arthroplasty (n=9, 50%) or debridement and implant retention (n=5, 28%). Thirty seven percent (n=7) were treated with metronidazole. Eighty percent (n=4) of patients that failed therapy had undergone debridement and retention of their prosthesis, as compared to none of those treated with resection arthroplasty. Seventy percent (n=14) of patient episodes were infection free at their last date of follow up. In conclusion, a significant proportion of patients with Bacteroides PJI are immunosuppressed and have an underlying GI or GU tract pathology. Retention and debridement of the prosthesis is associated with a higher risk of treatment failure.

Prevention of Infection in Orthopedic Prosthetic Surgery

Total joint arthroplasty is a generally safe orthopedic procedure; however, infection is a potentially devastating complication. Multiple risk factors have been identified for development of prosthetic joint infections. Identification of patients at risk and preoperative correction of known risk factors, such as smoking, diabetes mellitus, anemia, malnutrition, and decolonization of Staphylococcus carriers, represent well-established actions to decrease the infection risk. Careful operative technique, proper draping and skin preparation, and appropriate selection and dosing of antimicrobials for perioperative prophylaxis are also very important in prevention of infection.

Prevention of Biomaterial Infection by Pre-Operative Incubation with Human Cells

BACKGROUND

Cells of tissues and biofilm forming bacteria compete for the living space on the surface of an implant. We hypothesized the incubation of the implant (titanium, polydimethylsiloxane, and polystyrene surface) with human cells before implantation as a strategy to prevent bacterial adhesion and biofilm formation.

METHODS

After 24 hours of incubation with human osteogenic sarcoma SaOS-2 cells (1 × 10⁵ cells/mL), the materials were incubated for 4.5 hours or two days with Staphylococcus aureus in serial 1:10 dilutions of 10⁸ colony-forming units/mL. The bacterial adherence and biofilm biomass on materials pre-incubated with SaOS-2 cells were compared with our previous results on materials incubated only with bacteria or in simultaneous co-culture of SaOS-2 cells and S. aureus. Fluorescent microscopy and crystal violet stain were used. The number of viable SaOS-2 and bacterial cells present was tested using colorimetric methods (MTT, LDH) and drop plate method, respectively.

RESULTS

The pre-treatment with human cells was associated with a reduction of bacterial colonization of the biomaterial at 4.5 hours and 48 hours compared with the non-pre-treated materials. The presence of bacteria decreased the number of viable human cells on all materials. ( Supplementary Fig. 1 ; see online supplementary materials at www.liebertpub.com/sur ).

CONCLUSIONS

These results suggest that the pre-operative incubation of prostheses with host cells could prevent infection of biomaterials.

Utility of 16S rRNA PCR performed on clinical specimens in patient management

BACKGROUND

Broad-range 16S rRNA PCR can be used for the detection and identification of bacteria from clinical specimens in patients for whom there is a high suspicion of infection and cultures are negative. The aims of this study were (1) to compare 16S rRNA PCR results with microbiological culture results, (2) to assess the utility of 16S rRNA PCR with regard to antimicrobial therapy, and (3) to compare the yield of 16S rRNA PCR for different types of clinical specimen and to perform a cost analysis of the test.

METHODS

A retrospective study was performed on different clinical specimens which had 16S performed over 3 years (2012-2015). Standard microbiological cultures were performed on appropriate media, as per the laboratory protocol. Patient clinical and microbiological data were obtained from the electronic medical records and laboratory information system, respectively. 16S rRNA PCR was performed in a reference laboratory using a validated method for amplification and sequencing. The outcomes assessed were the performance of 16S rRNA PCR, change of antimicrobials (rationalization, cessation, or addition), and duration of therapy. Concordance of 16S rRNA PCR with bacterial cultures was also determined for tissue specimens.

RESULTS

Thirty-two patients were included in the study, for whom an equal number of specimens (n=32) were sent for 16S rRNA PCR. 16S rRNA PCR could identify an organism in 10 of 32 cases (31.2%), of which seven were culture-positive and three were culture-negative. The sensitivity was 58% (confidence interval (CI) 28.59-83.5%) and specificity was 85% (CI 61.13-96%), with a positive predictive value of 70% (CI 35.3-91.9%) and negative predictive value of 77.2% (CI 54.17-91.3%). Antimicrobial therapy was rationalized after 16S rRNA PCR results in five patients (15.6%) and was ceased in four based on negative results (12.5%). Overall the 16S rRNA PCR result had an impact on antimicrobial therapy in 28% of patients (9/32). The highest concordance of 16S rRNA PCR with bacterial culture was found for heart valve tissue (80%), followed by joint fluid/tissue (50%).

CONCLUSIONS

Despite the low diagnostic yield, results of 16S rRNA PCR can still have a significant impact on patient management due to rationalization or cessation of the antimicrobial therapy. The yield of 16S rRNA PCR was highest for heart valves.

The role of RANKL/RANK/OPG system in the canine model of hip periprosthetic infection osteolysis

Purpose

We aimed to investigate whether the RANKL/RANK/OPG system is associated with the incidence of periprosthetic osteolysis with septic loosening, and to investigate the differences of RANKL/RANK/OPG system expression in synovial fluid surrounding the normal and septic loosening hip prosthesis in canine models.

Methods

Twelve healthy adult mongrel canines were divided into two groups: experimental and control. Femoral head and stem replacements were conducted on the right side in both groups. The experimental group received the bacteria fluid intra-articular injection and the other group received the same amount of saline in the same day. The synovial fluid samples were gathered at the 1st, 2nd, 4th, 8th, 12th, 16th and 19th week after the bacteria fluid intra-articular injection for enzyme-linked immunosorbent assay (ELISA), the expression of the RANKL/RANK/OPG system.

Results

Surgery on all animals was successful. Two dogs were excluded from the analysis of the result because of a surgery infection or death. The ELISA of the synovial fluid revealed that the ratio of RANKL/OPG showed a significant upward trend (p≤0.05) with time in the test group but the ratio of RANKL/OPG in the control group changed slowly over time (p>0.05). The ratio of RANKL/OPG value between the test and control group showed a significant upward trend, but had no statistical difference (p>0.05) over time.

Conclusions

It could be concluded that the RANKL/RANK/OPG system is correlated with the incidence of periprosthetic osteolysis with septic loosening. Consequently, imbalance RANKL/RANK/OPG system was related to periprosthetic osteolysis with septic loosening.

Prosthetic Joint Infection due to Mycobacterium avium-intracellulare in a Patient with Rheumatoid Arthritis: A Case Report and Review of the Literature

Nontuberculous mycobacteria (NTM) are a rare cause of prosthetic joint infections (PJI). However, the prevalence of NTM infections may be increasing with the rise of newer immunosuppressive medications such as biologics. In this case report, we describe a rare complication of immunosuppressive therapies and highlight the complexity of diagnosing and treating PJI due to NTM. The patient is a 79-year-old Caucasian male with a history of severe destructive rheumatoid arthritis on several immunosuppressive agents and right hip osteoarthritis s/p total hip arthroplasty 15 years previously with several complex revisions, presenting with several weeks of worsening right hip and abdominal pain. A right hip CT scan revealed periprosthetic fluid collections. Aspiration of three fluid pockets was AFB smear-positive and grew Mycobacterium avium-intracellulare. The patient was deemed a poor surgical candidate. He underwent a limited I&D and several months of antimycobacterial therapy but clinically deteriorated and opted for hospice care. PJI caused by NTM are rare and difficult to treat. The increased use of biologics and prosthetic joint replacements over the past several decades may increase the risk of PJI due to NTM. A high index of suspicion for NTM in immunosuppressed patients with PJI is needed.

Candida Prosthetic Joint Infection. A Review of Treatment Methods

Fungal microorganisms are still a rare cause of bone and joint infections. We report a new case of knee prosthetic joint infection due to Candida albicans in a patient with a previous two-stage right knee arthroplasty for septic arthritis due to S. epidermidis occurred several months ago. Moreover, the treatment in 76 cases of Candida prosthetic joint infection has been discussed. Forty patients were female and mean age at diagnosis was 65.7 (± SD 18) yrs. No risk factors for candidal infection were found in 25 patients. Infection site was the knee in 38 patients and hip in 36; pain was present in 44 patients and swelling in 24. The most frequent species was C. albicans, followed by C. parapsilosis. Eleven patients were only treated with antifungal drugs being the outcome favourable in all of them. Two-stage exchange arthroplasty was performed in 30 patients, and resection arthroplasty in other 30; in three patients one-stage exchange arthroplasty was done. A favourable outcome was found in 58 patients after antifungal plus surgical treatment, in 11 after antifungal treatment alone and in one after surgery alone. The type of treatment is still not clearly defined and an algorithm for treatment in fungal PJI should be established, but various types of surgical procedures may be applied.

Microbiology and Antimicrobial Challenges of Prosthetic Joint Infection

Research that leads to better strategies to diagnose and treat prosthetic joint infection (PJI) is critical because PJI is a devastating complication of total knee arthroplasty. A key to the diagnosis and management of PJI is defining the microbiology of PJI and improving the medical management of PJI utilizing both systemic and local antimicrobial therapy. In this review, the author will present his opinions on future research needs as they relate to the microbiology of PJI, including antimicrobial resistance and the antimicrobial treatment of PJI. This paper summarizes a presentation given at a recent multidisciplinary research conference entitled "Strategies to improve total knee arthroplasty" sponsored by the Knee Society. It was a part of a session entitled "Periprosthetic Joint Infection."

Staphylococcal Biofilms and Immune Polarization During Prosthetic Joint Infection

Staphylococcal species are a leading cause of community- and nosocomial-acquired infections, where the placement of foreign materials increases infection risk. Indwelling medical devices and prosthetic implants are targets for staphylococcal cell adherence and biofilm formation. Biofilm products actively suppress proinflammatory microbicidal responses, as evident by macrophage polarization toward an anti-inflammatory phenotype and the recruitment of myeloid-derived suppressor cells. With the rise in prosthetic hip and knee arthroplasty procedures, together with the recalcitrance of biofilm infections to antibiotic therapy, it is imperative to better understand the mechanism of crosstalk between biofilm-associated bacteria and host immune cells. This review describes the current understanding of how staphylococcal biofilms evade immune-mediated clearance to establish persistent infections. The findings described herein may facilitate the identification of novel treatments for these devastating biofilm-mediated infections.

Rifampin-Based Combination Therapy Is Active in Foreign-Body Osteomyelitis after Prior Rifampin Monotherapy

Staphylococcal prosthetic joint infections (PJIs) are associated with biofilm formation, making them difficult to treat; if managed with debridement and implant retention, rifampin-based therapy is usually employed. Rifampin resistance potentially challenges PJI treatment. In investigating the effects of rifampin monotherapy on methicillin-resistant Staphylococcus aureus (MRSA) foreign-body osteomyelitis in rats, we previously demonstrated that rifampin resistance was selected but that it disappeared 14 days following rifampin monotherapy (1) and that rifampin resistance occurred less frequently following two rounds than following one round of rifampin monotherapy (2). Here, we compared rifampin monotherapy followed by rifampin-vancomycin combination therapy to rifampin-vancomycin combination therapy alone in experimental MRSA foreign-body osteomyelitis. Animals treated with rifampin monotherapy followed by rifampin-vancomycin combination therapy had decreased quantities of bacteria 14 days following treatment completion (P = 0.034) compared to those in animals treated with combination therapy alone. Additionally, some isolates recovered from animals treated with combination therapy alone, although still susceptible to rifampin, had higher MIC, minimum biofilm-inhibitory concentration (MBIC), and minimum biofilm-bactericidal concentration (MBBC) values than those of the inoculating strain. This suggests that rifampin may remain a feasible treatment option in foreign-body-associated orthopedic infections following the selection of rifampin resistance.

Activity of Electrical Current in Experimental Propionibacterium acnes Foreign-Body Osteomyelitis

Foreign-body-associated infections are often difficult to treat, given that the associated microorganisms are in a biofilm state. Previously, we showed that a low-amperage direct electrical current (DC) reduces Propionibacterium acnes biofilms formed on implant-associated materials in vitro In this study, low-amperage DC was compared to ceftriaxone treatment or no treatment in a novel rat femur model of foreign-body osteomyelitis. A platinum implant seeded with a P. acnes biofilm (10⁷ CFU/cm²) and 10⁹ CFU of planktonic P. acnes was placed in the femoral medullary cavity. One week later, rats were assigned to one of three treatment groups: no treatment, ceftriaxone treatment, or 200-μA-DC treatment. After 2 weeks of treatment, there were fewer bacteria in the bones of the ceftriaxone group (3.06 log₁₀ CFU/g of bone [P = 0.0209]) and the 200-μA-DC group (0.5 log₁₀ CFU/g [P = 0.0015]) than in those of the control group (6.58 log₁₀ CFU/g). The DC-exposed animals exhibited fewer bacteria than the ceftriaxone-treated animals (P = 0.0330). There were fewer bacteria on the implanted wires in the groups treated with ceftriaxone (0.1 log₁₀ CFU/cm²) or a 200-μA DC (0.1 log₁₀ CFU/cm²) than in the control group (2.53 log₁₀ CFU/cm² [P, 0.0003 for both comparisons]). Low-amperage DC may be useful for treating, or aiding in the treatment of, foreign-body infections caused by P. acnes.