Anaerobic prosthetic joint infection

Prosthetic joint infection caused by Mediterraneibacter gnavus following total knee arthroplasty, challenges in anaerobic bacteria identification

BACKGROUND

Mediterraneibacter gnavus is a Gram positive, non-sporulated, obligate anaerobe diplococci. It was first described in 1974 by Moore et al. (under the name Ruminococcus gnavus) from faeces and contents of the gastrointestinal tract of humans. It is a relatively common member of the human gut microbiota, nevertheless its role as a pathogenic bacterium has not been completely elucidated yet and it seems to depend on numerous factors, including those of the host. Here we present a case of prosthetic joint infection following total knee arthroplasty by M. gnavus.

CASE PRESENTATION

A 74 years old patient was admitted to the emergency department presenting with acute onset of left knee pain and swelling 20 days after total left knee arthroplasty. Follow-up revealed erythema and oedema without signs of fluctuation or purulent discharge from the surgical wound and elevated inflammatory reactants. Synovial fluid was taken for bacterial culture and antibiotic treatment with ceftazidime and daptomycin was established. Examination of the synovial fluid revealed abundant polymorphonuclear leucocytes, without visualizing bacteria. After four days of incubation, anaerobic culture exhibit growth of small, grey, umbilicated colonies in pure culture on Schaedler agar. The microorganism was identified as R. gnavus by MALDI-TOF (Bruker Daltonics) and M. gnavus by 16S ribosomal bacterial sequencing. The isolated showed susceptibility to the most commonly used anaerobicidal antibiotics except for clindamycin. Surgical treatment and infection source control included DAIR (debridement, antibiotics, and implant retention) and vacuum assisted therapy. The patient was discharged after six weeks with a 3-month course of oral amoxicillin as consolidation therapy. Subsequent follow-up revealed adequate wound healing with no signs of infection.

CONCLUSIONS

Mediterraneibacter gnavus have been reported as the causal microorganism in a range of human infections, nevertheless its identification remains challenging. Infection of prosthetic joints by anaerobic microorganisms is uncommon and is not considered in its empirical antibiotic treatment, thus, correct and swift identification of anaerobic bacteria in these cases is paramount.

Total hip arthroplasty in patients with colostomy: impact on inpatient complications, hospital costs, and length of stay

INTRODUCTION

The presence of permanent end-colostomy is traditionally thought of as a risk factor for complications following orthopedic joint replacement; however, literature supporting this association is scarce. This study aims to discern how length of stay, cost of stay, and inpatient complications following total hip arthroplasty (THA) are impacted by presence of colostomy.

METHODS

Data from the National Inpatient Sample was analyzed by International Classification of Diseases, 10th Revision, Clinical Modification regarding THA in patients with and without end-colostomy. Unmatched and matched analyses comparing length of stay, cost of stay, and post-operative adverse outcomes between the two groups were conducted. In the unmatched analysis, 445 THA patients with colostomy were compared to 367,449 THA patients without colostomy. The colostomy patients were then matched for age, sex, race, diabetes, obesity, and the matched groups consisted of 445 patients with and 425 patients without colostomy, respectively.

RESULTS

Compared to the THA without colostomy group, the colostomy group was significantly older, had longer hospital stays, and greater cost of stay. When matched for age and comorbidities, length of hospital stay (p < 0.001) and cost of stay (p = 0.002) remained significantly higher. The colostomy group was at significantly increased risk for periprosthetic fracture, dislocation, and infection compared to all THA patients. When matched for age and common comorbidities, the colostomy group had significantly higher risk in only periprosthetic dislocation [p = 0.003, OR 11.8 (1.6-4.6, 95% CI)] and periprosthetic infection [p < 0.05, OR 2.7 (0.97-7.7 95% CI)].

CONCLUSION

Patients with colostomy are at risk of longer hospital courses and greater incurred costs following THA compared to patients without colostomy. They are additionally at significantly increased risk of periprosthetic dislocation and periprosthetic infection, warranting treatment as high-risk patients.

STUDY DESIGN

Retrospective cohort study.

Clostridial prosthetic joint infections: A series of 16 cases and literature review

OBJECTIVES

Prosthetic joint infections (PJIs) due to the Clostridium species have not been widely investigated. We aimed to characterize these uncommon infections.

METHODS

We conducted a retrospective study between 2003 and 2020 in six French hospitals combined with a review of the literature.

RESULTS

The main conclusions obtained from the 16 patients included were reinforced by the literature analysis: (i) Clostridium perfringens was the most frequently involved species, (ii) patients presented an advanced age at the time of prosthesis placement and infection, (iii) most of the infections were early- or delayed-onset, (iv) the prognosis for these PJIs remains poor, (v) when performed (n = 5), DAIR with 12-week antimicrobial therapy led to a favorable outcome in 80% of cases.

CONCLUSIONS

Given the low incidence of this infection, our work represents the largest series of clostridial PJIs reported to date and highlights some specificities of these infections. Further prospective studies are needed to confirm these results.

First periprosthetic hip infection caused by Eggerthella lenta

Periprosthetic joint infection (PJI) caused by anaerobic, Gram-positive bacilli is rare. We present here a case of an 83-year-old female patient who was admitted to our tertiary referral arthroplasty center to treat a complex PJI of her right hip joint after multiple failed surgeries. External and intraoperative cultures reveald growth of Eggerthella lenta (E. lenta). Microbiological identification was fast but in a very few samples. A successful management, comprising of radical debridement with one-stage exchange and an antibiotic treatment with multiple antibiotics, has been achieved at 24-month follow-up. To the best of our knowledge, we have provided the first case study of a hip PJI caused by E. lenta successfully treated with one-stage exchange and an adequate antibiotic treatment.

Prosthetic knee joint infection caused by α-hemolytic Streptococcus species: a case report

BACKGROUND

Knee arthroplasty is an orthopedic surgical procedure in which a damaged joint is replaced with an artificial one. It is estimated that 1-2% of knee arthroplasties will encounter infection over their lifetime. Although α-hemolytic Streptococcus species play an important role in prosthetic joint infection, they are less common than staphylococcal species.

CASE PRESENTATION

In this report, a 50-year-old Iranian woman was diagnosed with prosthetic knee joint infection based on clinical, radiological, and laboratory findings. She was diabetic and had undergone a left total knee arthroplasty, which, 18 months after the surgery, presented pain, erythema, and edema in that knee. The primary culture of knee aspirate was positive for α-hemolytic Streptococcus species, but following antibiotic medication, culture was negative. The primary antibiotic regime was vancomycin and meropenem, which was changed to cefepime for the management of the infection based on the results of antimicrobial susceptibility testing.

CONCLUSIONS

This report indicated the clinical presentation and management of the patient with prosthetic joint infection in which the patient recovered without any severe complications or surgical intervention.

Clinical pointers in Prevotella septic arthritis of the hip: a case report

BACKGROUND

Infective arthritis is an orthopaedic surgical emergency. Staphylococcus aureus remains the commonest causative bacteria across all age groups. Prevotella spp. as a cause of infective arthritis is extremely rare.

CASE REPORT

We present our case of a 30-year-old African male patient who presented with mild signs of infective arthritis of the left hip. His risk factors were his background retroviral disease, intravenous drug abuse, and a previous episode of left hip arthrotomy which healed expectantly with intervention. The current presentation was treated with arthrotomy of the hip, fluid lavage, and skeletal traction based on our clinical findings and the rarity of the presentation was seen to be mobilising non-weight bearing with crutches, and pain-free on the left hip.

CONCLUSION

A high index of suspicion for Prevotella Septic Arthritis (PSA) should be exercised when treating infective arthritis patients with background joint arthropathies, and intravenous drug abuse, especially in individuals with significant immunosuppression and/or recent tooth extraction. Fortunately, although rare an entity, good outcomes can be expected with early diagnosis and classic treatment principles of joint decompression and lavage as well as guided antibiotic therapy.

Microbiology of chronic mesh infection

PURPOSE

Mesh infection following hernia repair is one of the most dreaded complications of hernia surgery. Mesh sinus, infected seromas, mesh extrusion, and mesh-related enteric fistulas are common complications associated with synthetic mesh. This study aimed to review the microbiota of mesh infection in 100 patients submitted to mesh explantation.

METHODS

We reviewed the charts of patients presenting with a history of mesh infection lasting or arising six months or more after mesh placement. All patients who submitted to abdominal wall repair with complete removal of an infected mesh and presenting a positive culture were included. The microbiology analysis was based on positive cultures obtained from the fluids and tissues surrounding the mesh or positive cultures of the mesh. Microorganisms were divided into gram-positive or gram-negative, aerobic or anaerobic, and fungi.

RESULTS

Pure aerobic gram-positive cultures were encountered in 50% of the patients, followed by a combination of aerobic gram-positive/gram-negative (8%) and pure gram-negative cultures (6%). Anaerobes were recovered from 31% of patients. Fungi were recovered from 6%. Staphylococcus aureus was identified in 64% of cultures, with methicillin-resistant Staphylococcus aureus present in 42% and methicillin-sensitive Staphylococcus aureus in 22%. Among aerobic gram-negative infections, six (17%) were caused by multi-resistant bacteria, including Pseudomonas aeruginosa, Proteus mirabilis, Acinetobacter baumanii, Klebsiella pneumoniae complex, and Enterobacter cloacae complex.

CONCLUSION

Staphylococcus aureus plays a significant role in the pathogenesis of synthetic mesh infection. Staphylococcus aureus, isolated in 64% of cultures, accounted for most single bacterial infections and was the prevalent germ in mesh sinus and infected seromas. Gram-negative infection occurred in 35%. Anaerobes occurred in 31%, commonly encountered in polymicrobial infections. Most fungi cultures happened in patients with enteric fistulas.

Microbiological profiles and antibiotic resistance of periprosthetic joint infection after hip replacement in patients with fracture or non-fracture: A comparative study

BACKGROUND

Periprosthetic joint infection (PJI) is one of the worst complications following total joint arthroplasty (TJA). Unfortunately, effective prevention strategies to reduce the burden of PJI have not been fully determined in hip replacement patients with fracture and non-fracture.

OBJECTIVE

This study aimed to analyze and compare the demographic characteristics, microbiological profiles and antibiotic resistance of PJI after hip replacement between patients with fracture and non-fracture.

METHODS

We retrospectively analyzed the data of 132 patients who treated PJI. There were divided into two groups: non-fracture group (64 patients infected after hip replacement for fracture) and non-fracture group (68 patients infected after hip replacement for non-fracture). Microorganisms were obtained from the synovial fluid and infected necrotic tissue in the joint capsule, medullary cavity, or acetabulum in all patients, and microbiological profiles and antibiotic resistance were evaluated.

RESULTS

Coagulase-negative staphylococci (CoNS) were the most common pathogenic microorganisms in all patients. Methicillin-resistant Staphylococcus (MRS) accounted for 25% in all pathogenic microbes. Staphylococci showed high drug resistance rates to clindamycin, levofloxacin, and all of the first- and second-generation cephalosporins. MRS isolates in non-fracture group had higher drug resistance rates to clindamycin and levofloxacin than than those in fracture group. Gram-negative bacilli (GNB) showed high drug resistance rates to Aztreonam, gentamicin and all of the third- and fourth-generation cephalosporins. Furthermore, GNB isolates in the non-fracture group showed higher resistance rates to gentamicin and all of the third- and fourth-generation cephalosporins.

CONCLUSIONS

MRS isolates in the non-fracture group showed higher drug resistance rates to clindamycin and levofloxacin, and GNB isolates in non-fracture group showed higher drug resistance rates to gentamicin and all of the third- and fourth-generation cephalosporins.

A first case of prosthetic joint infection with Actinomyces radingae

Prosthetic joint infection is a common clinical orthopedic problem but infections caused by Actinomyces species have been rarely reported. An increasing number of reports identifying Actinomyces in cases of prosthetic joint infection suggest it may be an emerging pathogen. We describe here the first known case of a prosthetic joint infection caused by Actinomyces radingae.

C9 immunostaining as a tissue biomarker for periprosthetic joint infection diagnosis

Background

Culture-negative periprosthetic joint infections (PJI) are often false diagnosed as aseptic implant failure leading to unnecessary revision surgeries due to repeated infections. A marker to increase the security of e PJI diagnosis is therefore of great importance. The aim of this study was to test C9 immunostaining of periprosthetic tissue as a novel tissue-biomarker for a more reliable identification of PJI, as well as potential cross-reactivity.

Method

We included 98 patients in this study undergoing septic or aseptic revision surgeries. Standard microbiological diagnosis was performed in all cases for classification of patients. Serum parameters including C-reactive protein (CRP) serum levels and white blood cell (WBC) count were included, and the periprosthetic tissue was immunostained for C9 presence. The amount of C9 tissue staining was evaluated in septic versus aseptic tissue and the amount of C9 staining was correlated with the different pathogens causing the infection. To exclude cross-reactions between C9 immunostaining and other inflammatory joint conditions, we included tissue samples of a separate cohort with rheumatoid arthritis, wear particles and chondrocalcinosis.

Results

The microbiological diagnosis detected PJI in 58 patients; the remaining 40 patients were classified as aseptic. Serum CRP values were significantly increased in the PJI cohort. Serum WBC was not different between septic and aseptic cases. We found a significant increase in C9 immunostaining in the PJI periprosthetic tissue. To test the predictive value of C9 as biomarker for PJI we performed a ROC analyses. According to the Youden's criteria C9 is a very good biomarker for PJI detection with a sensitivity of 89% and a specificity of 75% and an AUC of 0.84. We did not observe a correlation of C9 staining with the pathogen causing the PJI. However, we observed a cross reactivity with the inflammatory joint disease like rheumatoid arthritis and different metal wear types. In addition, we did not observe a cross reactivity with chondrocalcinosis.

Conclusion

Our study identifies C9 as a potential tissue-biomarker for the identification of PJI using immunohistological staining of tissue biopsies. The use of C9 staining could help to reduce the number of false negative diagnoses of PJI.

Periprosthetic Hip Joint Infection with Flavonifractor plautii: A Literature Review and Case Report

The purpose of this case report and review of the literature is to provide documentation on periprosthetic hip joint infection with Flavonifractor plautii (formerly known as Eubacterium plautii), a strictly anaerobic bacterium, and to report on a successful pathway for management including staged surgical revisions and extended antibiotic therapy. A systematic review of the literature was conducted, which identified this case as only the fifth documented case of human infection with this organism; as a result, conduct of further research is warranted, based on the paucity of reports in the literature addressing anaerobic periprosthetic joint infection.

Periprosthetic Joint Infection With Actinomyces radingae May Lead to the Identification of a Neglected Source of Intraoperative Contamination

Periprosthetic joint infection remains a major complication in arthroplasty. We present the first description of a case of periprosthetic joint infection with Actinomyces radingae, microorganism that is mostly found on the skin of the upper body and might cause particular challenges as it is difficult to culture and specify. Furthermore, a thorough microbiologic workup may indicate the source of infection. In this case, it is possible that perspiration from the surgeon was the source of intraoperative contamination. Intraoperative contamination through perspiration may be important and should be avoided by all means.

Increased rate of enteric bacteria as cause of periprosthetic joint infections in patients with liver cirrhosis

Introduction

Periprosthetic joint infections (PJI) are a major complication in joint-arthroplasty. Rifampicin is often used as an additional agent to treat PJI, because it penetrates bacterial biofilms. However, rifaximin, belonging to the same antibiotic class as rifampicin, is frequently used to prevent episodes of hepatic encephalopathy in patients with cirrhosis and may induce resistance to rifampicin. The aim of this study was to examine the microbial pattern of periprosthetic joint infections in cirrhotic patients and to test the hypothesis that intake of rifaximin increases the rate of resistance to rifampicin in periprosthetic joint infections.

Methods

A cohort of cirrhotic patients and PJI (n = 25) was analysed on the characteristics of bacterial isolates from sonication and tissue analysis. In a second step a subgroup analysis on the development of rifampicin resistant bacterial specimens, depending on the intake of rifaximin (8 rifaximin intake patients vs. 13 non rifaximin intake patients) was performed.

Results

Intestinal bacteria were found in 50% of the specimens, which was significantly more frequent than in a control cohort. By comparison of the single bacterial isolates, rifampicin resistance was detected in 69.2% (9/13) of the rifaximin-intake samples. In contrast, the non-rifaximin-intake isolates only were resistant to rifampicin in 22.2% (4/18) of the cases (p = 0.01). The odds ratio for developing a rifampicin-resistance through rifaximin intake was calculated as OR = 13.5.

Conclusion

Periprosthetic joint infections have a high incidence of being caused by enteric bacteria in cirrhotic patients. Due to this change in microbial pattern and the innate resistance to rifampicin of most of gram-negative bacteria, the therapy with rifampicin should be carefully considered. The association between the use of rifaximin and developed resistance to rifampicin has a major impact on the treatment of PJI.

Diagnosis of orthopaedic-implant-associated infections caused by slow-growing Gram-positive anaerobic bacteria - a clinical perspective

Slow-growing Gram-positive anaerobic bacteria (SGAB) such as Cutibacterium acnes are increasingly recognized as causative agents of implant-associated infections (IAIs) in orthopaedic surgeries. SGAB IAIs are difficult to diagnose because of their non-specific clinical and laboratory findings as well as the fastidious growth conditions required by these bacteria. A high degree of clinical suspicion and awareness of the various available diagnostic methods is therefore important. This review gives an overview of the current knowledge regarding SGAB IAI, providing details about clinical features and available diagnostic methodologies. In recent years, new methods for the diagnosis of IAI were developed, but there is limited knowledge about their usefulness in SGAB IAI. Further studies are required to determine the ideal diagnostic methodology to identify these infections so that they are not overlooked and mistakenly classified as aseptic failure.

Late onset prosthetic joint infection caused by Parvimonas micra

Parvimonas micra (P.micra) is a difficult to culture gram positive anaerobic microorganism, typically found in the human microbiota, specially in the oral cavity. There are limited cases in literature reporting prosthetic joint infection due to this bacteria, although its isolation has been reported in different settings in later years. We present the case of a late onset knee prosthetic joint infection caused by Parvimonas micra in an 87 year old woman treated with antibiotics and two-step surgery with prosthetic material removal, antibiotic-loaded cement spacer placement and new prosthetic material replacement after 2 weeks of intravenous antimicrobial therapy followed by 6 weeks of oral therapy.

Genomic Analysis of Cutibacterium acnes Strains Isolated from Prosthetic Joint Infections

Cutibacterium acnes is a common cause of prosthetic joint infections (PJIs). The C. acnes population can be divided into six main phylotypes (IA₁, IA₂, IB, IC, II and III) that are associated with different clinical conditions and normal skin. A single-locus sequence typing (SLST) scheme can distinguish ten main SLST types: A-E (all IA₁), F (IA₂), G (IC), H (IB), K (II), L (III). We genome-sequenced and compared 16 strains of C. acnes isolated from healthy skin (n = 4) and PJIs (n = 12), including six PJI cases with a good outcome (four shoulder PJIs, one hip PJI, one knee PJI) and six with infection relapse (three shoulder PJIs, three hip PJIs). The sequenced strains belonged to four different phylotypes (IA₁, IA₂, IB and II) and seven different SLST types. All five type IB strains (all SLST type H1) were PJI isolates (three hip PJIs, two shoulder PJIs), and four of these caused infection relapse (three hip PJIs, one shoulder PJI). Isolates from PJI cases with a good outcome belonged to three different phylotypes (IA, IB, II). Interestingly, four strains (three strains from PJI cases with good outcome and one strain from healthy skin) contained a linear plasmid; these strains belonged to different SLST types (A1, C1, F4, H1) and were isolated in three different hospitals. This study suggests that type IB strains have the potential to cause infection relapse, in particular regarding hip PJIs. Moreover, our study revealed that strains belonging to the same SLST type can differ in their accessory genome in different geographic locations, indicative of microevolution.

Clinical and microbiological features of anaerobic implant-related infection in 80 patients after orthopedic surgery

OBJECTIVES

Implant-related infection is a common complication after orthopedic surgery, but there is limited research focused on anaerobic infections. We retrospectively analyzed data from 80 patients with anaerobic implant-related infections in order to investigate the clinical features, bacterial distribution and antimicrobial resistant characteristics of this disease.

METHODS

80 patients who underwent implant-related infections with anaerobes were included. Pathogens were isolated and identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectrometry with verification of 16s rRNA sequencing. Antimicrobial susceptibility testing (AST) was performed using Epsilometric test (E-test).

RESULTS

Among the 80 patients, 61.2% (49/80) were infected with anaerobes alone, while 38.8% (31/80) were co-infected with anaerobes and other bacteria. Early infection cases involving anaerobe-alone infections were significantly higher compared to the co-infection group (P < 0.001), also exhibiting lower levels of neutrophils (P = 0.033) and ESR (P = 0.046). Anaerobe-alone infections in the prosthetic joint infection group represented a higher proportion compared with other implant-related infections (P = 0.031). Among all species of anaerobes identified, the top 3 were Cutibacterium acnes, Finegoldia magna and Peptostreptococcus anaerobius. Low MIC values to vancomycin was recorded in C. acnes strains and for amoxicillin/clavulanic acid and piperacillin/tazobactam in most F. magna strains. One of the C. acnes and F. magna strains appeared multi-drug resistant except to vancomycin.

CONCLUSIONS

Anaerobe-alone infections have later first onset times and lower infection biomarker levels compared to co-infected patients. The first choice against C. acnes is vancomycin, while amoxicillin/clavulanic acid and piperacillin/tazobactam are recommended for F. magna.

A Janus-Faced Bacterium: Host-Beneficial and -Detrimental Roles of Cutibacterium acnes

The bacterial species Cutibacterium acnes (formerly known as Propionibacterium acnes) is tightly associated with humans. It is the dominant bacterium in sebaceous regions of the human skin, where it preferentially colonizes the pilosebaceous unit. Multiple strains of C. acnes that belong to phylogenetically distinct types can co-exist. In this review we summarize and discuss the current knowledge of C. acnes regarding bacterial properties and traits that allow host colonization and play major roles in host-bacterium interactions and also regarding the host responses that C. acnes can trigger. These responses can have beneficial or detrimental consequences for the host. In the first part of the review, we highlight and critically review disease associations of C. acnes, in particular acne vulgaris, implant-associated infections and native infections. Here, we also analyse the current evidence for a direct or indirect role of a C. acnes-related dysbiosis in disease development or progression, i.e., reduced C. acnes strain diversity and/or the predominance of a certain phylotype. In the second part of the review, we highlight historical and recent findings demonstrating beneficial aspects of colonization by C. acnes such as colonization resistance, immune system interactions, and oxidant protection, and discuss the molecular mechanisms behind these effects. This new insight led to efforts in skin microbiota manipulation, such as the use of C. acnes strains as probiotic options to treat skin disorders.

Antimicrobial susceptibility profiles of invasive isolates of anaerobic bacteria from a large Canadian reference laboratory: 2012-2019

Anaerobic bacteria can cause severe and life threatening infections. Susceptibility data are relatively limited on anaerobic organisms despite the clinical importance in guiding empiric treatment of infections. To determine antimicrobial susceptibility profiles of clinically significant anaerobic bacteria, isolates obtained from sterile sites submitted to Public Health Ontario Laboratory (2012-2019) were included in this study (N = 5712). Cefoxitin, clindamycin, metronidazole, meropenem, penicillin and piperacillin-tazobactam were tested using the gradient strip method with MICs interpreted based on Clinical and Laboratory Standards Institute guidelines. Bacteroides spp. (N = 958; 16.7%), Clostridium spp. (N = 798; 14.0%), Cutibacterium spp. (N =659; 11.5%) and Actinomyces spp. (N = 551; 7.0%) were the most commonly isolated genera. Bacteroides fragilis isolates were susceptible to cefoxitin (88.4%), clindamycin (68.4%), metronidazole (96.0%), meropenem (99.0%) and piperacillin-tazobactam (98.4%). Other Bacteroides spp. showed reduced susceptibility to several antimicrobials. Clostridium spp. isolates were susceptible to penicillin (69.7%), clindamycin (69.7%) and cefoxitin (76.3%); C. perfringens and C. ramosum showed distinct susceptibility profiles. Susceptibility rates among anaerobes remained relatively unchanged over 8 years with a few exceptions: C. perfringens susceptibility to clindamycin decreased from 91.3% to 60% (p = 0.03); Clostridium spp. susceptibility to penicillin similarly decreased from 82.1% to 65.9% (p = 0.03); Eggerthella spp. susceptibility to piperacillin-tazobactam decreased from 100% to 24.3% (p < 0.001); B. fragilis group susceptibility to cefoxitin decreased from 70.4% to 48.2% (p = 0.05); and Parabacteroides spp. susceptibility to piperacillin-tazobactam decreased from 100% to 25% (p = 0.01). Our findings underscore the need for ongoing surveillance and periodic monitoring of antimicrobial resistance in order to guide empiric therapy.

Staphylococcus saccharolyticus Associated with Prosthetic Joint Infections: Clinical Features and Genomic Characteristics

The anaerobic coagulase-negative staphylococcal species Staphylococcus saccharolyticus is a member of the normal skin microbiota. However, S. saccharolyticus is rarely found in clinical specimens and its pathogenic potential is unclear. The clinical data of prosthetic hip (n = 5) and shoulder (n = 2) joint implant-associated infections where S. saccharolyticus was detected in periprosthetic tissue specimens are described. The prosthetic hip joint infection cases presented as “aseptic” loosening and may represent chronic, insidious, low-grade prosthetic joint infections (PJIs), eventually resulting in loosening of prosthetic components. All cases were subjected to one-stage revision surgery and the long-term outcome was good. The shoulder joint infections had an acute onset. Polymicrobial growth, in all cases with Cutibacterium acnes, was found in 4/7 patients. All but one case were treated with long-term administration of beta-lactam antibiotics. Whole-genome sequencing (WGS) of the isolates was performed and potential virulence traits were identified. WGS could distinguish two phylogenetic clades (clades 1 and 2), which likely represent distinct subspecies of S. saccharolyticus. Little strain individuality was observed among strains from the same clade. Strains of clade 2 were exclusively associated with hip PJIs, whereas clade 1 strains originated from shoulder PJIs. It is possible that strains of the two clades colonize different skin habitats. In conclusion, S. saccharolyticus has the potential to cause PJIs that were previously regarded as aseptic loosening of prosthetic joint devices.

Bone and joint infections caused by Clostridium perfringens: a case series

The objective of this study was to evaluate antimicrobial therapy outcomes of bone and joint infections (BJI) caused by Clostridium perfringens. We investigated remission of symptoms and the absence of relapse or reinfection during follow-up. Among the 8 patients with C. perfringens BJI, the type of infection was early prosthesis infection (n = 2), osteosynthetic device infection (n = 4), and chronic osteomyeletis (n = 2). Clindamycin-rifampicin combination was given in 4 cases and metronidazole in 4 cases. The overall success rate was 87.5%. Among the 7 patients who completed antibiotic treatment, the success rate was 100%. The clindamycin-rifampicin combination appeared to be effective in patients with C. perfringens BJI.

Antimicrobial Susceptibility Patterns and Wild-Type MIC Distributions of Anaerobic Bacteria at a German University Hospital: A Five-Year Retrospective Study (2015-2019)

Local antimicrobial susceptibility surveys are crucial for optimal empirical therapy guidelines and for aiding in antibiotic stewardship and treatment decisions. For many laboratories, a comprehensive overview of local antimicrobial susceptibility patterns of anaerobic bacteria is still lacking due to the long incubation time and effort involved. The present study investigates the antimicrobial susceptibility patterns and related clinical and demographic data of 2856 clinical isolates of anaerobic bacteria that were submitted for analysis to the Institute for Medical Microbiology and Hygiene of the Freiburg University Medical Center (a tertiary university medical center in Southern Germany) between 2015 and 2019. Antimicrobial susceptibility testing has been carried out according to the European Committee on Antimicrobial Susceptibility Testing (EUCAST) guideline. Minimum inhibitory concentration (MIC)₅₀ and MIC₉₀ for penicillin, metronidazole, moxifloxacin, and clindamycin were established for Gram-positive anaerobes and for ampicillin-sulbactam, meropenem, metronidazole, moxifloxacin, and clindamycin for Gram-negative anaerobes. The distribution of MIC-values for various antibiotics against anaerobic bacteria was also established, especially for those having no specific breakpoints according to EUCAST guidelines. Most clinically relevant anaerobic bacteria originated from general surgery, neurological, and orthopedic wards. A high proportion of isolates were resistant to moxifloxacin and clindamycin indicating the importance of their susceptibility testing before administration. Based on our study metronidazole and other β-lactam/β-lactamase inhibitor combinations such as ampicillin-sulbactam remain suitable for empirical treatment of infections with anaerobic bacteria.

Successful 6-Week Antibiotic Treatment for Early Surgical-site Infections in Spinal Surgery

BACKGROUND

The incidence of spinal surgical site infections (SSIs) remains stable at less than 10%. Surgical reinterventions may be hampered by decubitus, treatment-related adverse events, and cost. In the context of emergence of bacterial resistance, a short duration of antimicrobial treatment is of critical importance. If the duration of treatment for SSI is currently 12 weeks, the aim of our study was to assess the efficacy of an antimicrobial treatment shortened to 6 weeks.

METHODS

This prospective study was carried out from November 2014 to July 2016 in an 827-bed teaching hospital. After surgical management of SSIs, patients received broad-spectrum antibiotics intravenously for 10 days and orally for the remainder, for a total of 6 weeks. Success was defined as absence of relapse, superinfection, or surgical failure at the end of treatment and at 1-year follow-up.

RESULTS

Eighty-five patients were included in this study. The median delay between initial surgery and diagnosis of SSI was 16 days. In 65 cases (76.4%), SSIs were monomicrobial; among these, Staphylococcus aureus was found in 30 cases (46%). Failure was observed in 7 cases (8.2%), with more than half caused by anaerobic bacteria.

CONCLUSIONS

Surgical management of SSI followed by a 6-week antibiotic treatment is associated with favorable outcome. Anaerobic bacteria seem to play a role in the occurrence of relapses. A 6-week reduction in antibiotic treatment leads to reduction in cost and, likely, also to reduction in the emergence and spread of resistant microorganisms.

No differences in short-term outcomes between patients with anaerobic and aerobic culture positive prosthetic joint infection

BACKGROUND

Prosthetic joint infection (PJI) is a devastation complication of total joint arthroplasty that can result in poor patient outcomes. Anaerobic organisms make up a small proportion of PJI cases and are much less studied. Studies comparing patient outcomes in anaerobic PJI to outcomes in aerobic PJI are sparse. The purpose of this study was to compare the clinical presentation, duration of antibiotics, type of treatment provided, and final outcome between PJI patients with anaerobic infection and those with aerobic infection.

METHODS

This was a retrospective study of 26 patients who underwent treatment for PJI at a tertiary referral center. Eight patients with anaerobic PJI were compared to 18 patients with aerobic PJI in terms of clinical presentation, laboratory values, treatment duration, and functional outcome. Statistical analysis was performed on continuous variables of interest.

RESULTS

The results of our study showed that there are no differences in short term clinical outcomes between PJI patients with cultures positive for anaerobic vs aerobic organisms (38.9% vs 50% successfully treated). Inflammatory markers were higher in the aerobic group and patients in the anaerobic group tended to have fewer medical comorbidities.

CONCLUSION

PJI caused by anaerobic organisms results in poor patient outcomes similar to infection caused by aerobic organisms. There are some differences in clinical presentation between the two groups that can be explained by the fact that anaerobic organisms are of low virulence and result in indolent infections causing longstanding symptoms.

Different microbiological profiles between hip and knee prosthetic joint infections

PURPOSE

The study aims to analyze the demographics and microbiological profiles of hip and knee prosthetic joint infection (PJI) and to compare the microbiological differences between hip and knee PJI.

METHODS

We performed a retrospective study of all PJI cases between January 2006 and December 2014 at a referral medical center in Taiwan.

RESULTS

A total of 294 PJI cases were collected: 159 were identified as hip PJI and 135 as knee PJI. The most common causative pathogen was Staphylococcus aureus (78 cases, 27%), followed by coagulase-negative staphylococci (CoNS, 42 cases, 14%). Methicillin-resistant staphylococci (MRS) accounted for 21% of all PJI cases. Fungus and mycobacterium were only involved in 12 cases (4.1%) of all PJI cases. Polymicrobial pathogens, anaerobes, and enteric gram-negative bacilli (GNB) were more likely to occur in hip joint prostheses than in knee joint prostheses (22 vs. 6 cases, p = 0.006; 11 vs. 0 cases; p = 0.002; 20 vs. 6 cases; p = 0.014, respectively).

CONCLUSION

The prevalence of polymicrobial pathogens, anaerobes, and enteric GNB was higher in the prosthetic hip infection than in the prosthetic knee infection. The high prevalence of MRS, including Methicillin-resistant (MR) S. aureus and MR-CoNS in PJI, may warrant the need for empiric antibiotic therapy with broader coverage while pending the culture result of PJI. Although fungal and mycobacterial PJI cases are rare, the incidence of these infections is relatively high in Taiwan. Fungus and mycobacterium should also be taken into consideration whenever a persistent PJI case is encountered.

Prosthetic joint infections present diverse and unique microbial communities using combined whole-genome shotgun sequencing and culturing methods

Introduction. Prosthetic joint infections (PJIs) are challenging to treat therapeutically because the infectious agents often are resistant to antibiotics and capable of abundant growth in surface-attached biofilms. Though infection rates are low, ca. 1-2 %, the overall increase in the sheer number of joint replacement surgeries results in an increase in patients at risk.Aims. This study investigates the consensus of microbial species comprising PJI ecology, which is currently lacking.Methodology. In this study, PJI populations from seven patients were analysed using combined culturing and whole-genome shotgun sequencing (WGSS) to establish population profiles and compare WGSS and culture methods for detection and identification of the PJI microbiome.Results. WGSS detected strains when culture did not, notably dormant, culture-resistant and rare microbes. The CosmosID algorithm was used to predict micro-organisms present in the PJI and discriminate contaminants. However, culturing indicated the presence of microbes falling below the WGSS algorithm threshold. In these instances, microbes cultured are believed to be minor species. The two strategies were combined to build a population profile.Conclusions. Variability between and among PJIs showed that most infections were distinct and unique. Comparative analysis of populations revealed PJIs to form clusters that were related to, but separate from, vaginal, skin and gut microbiomes. Fungi and protists were detected by WGSS, but the role of fungi is just beginning to be understood and for protists it is unknown. These micro-organisms and their novel and strain-specific microbial interactions remain to be determined in current clinical tests.

Prosthetic Joint Infection due to Actinomyces species: A case series and review of literature

Background: Actinomyces prosthetic joint infections (APJIs) are rare and optimal medical and surgical treatment strategies are unknown. The purpose of our study was to characterize the demographics, risk factors, management and outcomes of patients with PJIs due to Actinomyces spp. Methods: Using a retrospective cohort study design, the medical records of all patients with Actinomyces spp. total hip or knee arthroplasty infection (APJI) seen at a single institution between January 1, 1969 and December 31, 2016 were reviewed. We abstracted information including patient demographics, co-morbidities, joint age, surgical history, microbiology, management and outcomes. A simultaneous literature search via PubMed was performed to identify cases of APJI published in literature and a descriptive analysis was performed. Results: Eleven cases were identified over a 47 year study period at our institution. Seven patients (64%) were female. The median age at the time of diagnosis of infection was 71 years (range, 57-89). The knee was involved in six cases (55%) followed by the hip in 5 (45 %) cases. Three cases had dentures, broken teeth, or poor dentition. Actinomyces odonotlyticus was the most commonly found subspecies at our institution. Median ESR and CRP values were 61mm/hr and 64 mg/L respectively. Eight (72%) patients were managed with 2 stage exchange. Most patients received a course of beta-lactam therapy for 6 weeks. Ten cases (91%) were free of failure after a median duration of follow-up of 2 years (range, 0.67 - 5 years). The median duration from joint arthroplasty to the onset of symptoms was 162 days, range (20-3318). Six (54%) had a history of prior PJI with a different microorganism at the same joint site and 4 patients had history of prior 2 stage exchange (36%). In the literature group, we identified 12 cases and the most common subspecies was Actinomyces israelii; most patients underwent two stage exchange and were treated with 6 weeks of beta lactam antibiotics. Conclusions: Based on our observational study, Actinomyces PJI presents as a late complication of TJR, may be associated with prior PJI at the index joint and antecedent dental manipulation may portend as an additional risk factor. Treatment includes two stage exchange and beta- lactam therapy for 6weeks. These results will help clinicians in improved understanding and management of APJIs which although are rare but warrant special attention as population with implanted joint arthroplasties continues to rise.

Surgical site infection after hip replacement due to a novel Peptoniphilus species, provisionally named 'Peptoniphilus nemausus' sp. nov

We report a case of surgical site infection after total hip prosthesis replacement due to an ofloxacin-resistant Peptoniphilus isolate belonging to an unknown species for which the name 'Peptoniphilus nemausus' sp. nov. is proposed. Follow-up was favourable under clindamycin and rifampin for 3 months in this patient whom had a Proteus mirabilis infection treated by fluoroquinolone.

Staphylococcus saccharolyticus Isolated From Blood Cultures and Prosthetic Joint Infections Exhibits Excessive Genome Decay

The slow-growing, anaerobic, coagulase-negative species Staphylococcus saccharolyticus is found on human skin and in clinical specimens but its pathogenic potential is unclear. Here, we investigated clinical isolates and sequenced the genomes of seven strains of S. saccharolyticus. Phylogenomic analyses showed that the closest relative of S. saccharolyticus is Staphylococcus capitis with an average nucleotide identity of 80%. Previously sequenced strains assigned to S. saccharolyticus are misclassified and belong to S. capitis. Based on single nucleotide polymorphisms of the core genome, the population of S. saccharolyticus can be divided into two clades that also differ in a few larger genomic islands as part of the flexible genome. An unexpected feature of S. saccharolyticus is extensive genome decay, with over 300 pseudogenes, indicating ongoing reductive evolution. Many genes of the core metabolism are not functional, rendering the species auxotrophic for several amino acids, which could explain its slow growth and need for fastidious growth conditions. Secreted proteins of S. saccharolyticus were determined; they include stress response proteins such as heat and oxidative stress-related factors, as well as immunodominant staphylococcal surface antigens and enzymes that can degrade host tissue components. The strains secrete lipases and a hyaluronic acid lyase. Hyaluronidase as well as urease activities were detected in biochemical assays, with clade-specific differences. Our study revealed that S. saccharolyticus has adapted its genome, possibly due to a recent change of habitat; moreover, the data imply that the species has tissue-invasive potential and might cause prosthetic joint infections.

Clinical and Biological Features of Cutibacterium (Formerly Propionibacterium) avidum, an Underrecognized Microorganism

The recent description of the genus Cutibacterium has altered the taxonomy of Propionibacterium species. These organisms still belong to the genera of the skin coryneform group, and the most-studied species remains Cutibacterium acnes. Cutibacterium avidum is also a known skin commensal. This underrecognized microorganism can, however, act as a pathogen after bacterial seeding and can be considered opportunistic, causing either superficial or deep/invasive infections. It can cause numerous infections, including but not limited to breast infections, skin abscesses, infective endocarditis, and device-related infections. The ecological niche of C. avidum is clearly different from that of other members of the genus: it is found in the axillary region or at wet sites rather than in dry, exposed areas, and the number of microorganisms increases during puberty. Historically, it has been used for its ability to modulate the immune response and for its antitumor properties. Conventional microbial culture methods and identification processes allow for its accurate identification and characterization. Thanks to the modern omics tools used for phylogenomic approaches, understanding C. avidum pathogenesis (including host-bacterium interactions and virulence factor characterization) is becoming easier, allowing for more thorough molecular characterization. These analyses have revealed that C. avidum causes diverse diseases mediated by multiple virulence factors. The recent genome approach has revealed specific genomic regions within this species that are involved in adherence and biofilm formation as well as fitness, survival, and defense functions. Numerous regions show the presence of phages and horizontal gene transfer. C. avidum remains highly sensitive to a broad spectrum of antibiotics, such as β-lactams, fluoroquinolones, macrolides, and rifampin, although erythromycin and clindamycin resistance has been described. A long-term treatment regimen with a combination of antibiotics is required to successfully eliminate the remaining adherent bacteria, particularly in the case of deep infections after debridement surgery.

Periprosthetic joint infection caused by anaerobes. Retrospective analysis reveals no need for prolonged cultivation time if sensitive supplemented growth media are used

BACKGROUND

In microbiological diagnosis of periprosthetic joint infection (PJI) culture media and incubation time are controversially discussed, especially if anaerobic bacteria are the causative agent. This study was conducted to demonstrate the influence of sensitive supplemented growth media on the duration of culturing anaerobes.

METHODS

Twenty-five consecutive cases were included in this retrospective study. For definition of PJI, the criteria of the Musculoskeletal Infection Society (MSIS) were considered. Histopathological analysis was interpreted according to the classification by Krenn et al. The quantity and time to positivity of detected anaerobes were monitored. Furthermore, antimicrobial activity within the tissue and sonicate fluid was phenotypically tested.

RESULTS

In all cases, even if the patients had received antibiotics before recovery, culture of anaerobes (Propionibacterium species, Finegoldia magna, Parvimonas micra and Robinsoniella peoriensis), both from tissue samples and prosthetic components, first became detectable in supplemented liver thioglycollate broth within six days (median: four days).

CONCLUSION

Recommendations for prolonged cultivation for up to 14 days mostly aim at detection of anaerobes. Here we present a laboratory procedure that can shorten cultivation time considerably.

Finegoldia magna Isolated from Orthopedic Joint Implant-Associated Infections

The anaerobic Gram-positive coccus Finegoldia magna is a rare cause of infections of bone and joints. The aim of this study was to describe the microbiological and clinical characteristics of orthopedic implant-associated infections caused by F. magna We retrospectively analyzed samples consisting of anaerobic Gram-positive cocci and samples already identified as F. magna from patients with orthopedic infections. The isolates found were determined to the species level using matrix-assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF MS). The antibiotic susceptibility pattern was determined by Etest. Whole-genome sequencing (WGS) was performed. Clinical data were extracted from each patient's journal. In nine patients, orthopedic joint implant-associated infections were identified as being caused by F. magna The isolates were susceptible to most of the antibiotics tested, with the exception of rifampin and moxifloxacin in a few cases. Five of the nine infections were monomicrobial. The most common antibiotic used to treat the infection was penicillin V, but five of the nine patients received a combination of antibiotics. Eight patients underwent surgical treatment, with extraction of the implant performed in seven cases and reimplantation in only two cases. The WGS showed a relatively small core genome, with 126,647 single nucleotide polymorphisms identified within the core genome. A phylogenomic analysis revealed that the isolates clustered into two distinct clades. Orthopedic implant-associated infections caused by F. magna are rare, but the bacteria are generally susceptible to antibiotics. Despite this, surgical treatment combined with long-term antibiotics is often necessary. The WGS analysis revealed a high heterogeneity and suggested the existence of at least two different Finegoldia species.

Epidemiology and Antibiotic Resistance of Late Prosthetic Knee and Hip Infections

BACKGROUND

Prosthetic joint infections (PJI) are still a major complication of hip and knee arthroplasties. Identification of the causative pathogens and knowledge of their antibiotic susceptibilities are essential for the management of these infections. The main purpose of the study was to identify and compare the causative bacteria of prosthetic knee and hip joint infections in a reference Italian orthopedic center and to characterize antibiotic resistance profiles of bacteria involved.

METHODS

Data from 429 patients with diagnosis of PJI were collected from January 2013 to June 2015: 229 presented a hip and 200 a knee prosthesis infection. Prostheses and periprosthetic tissues were treated with dithiothreitol before plating onto different media and broths. Identification and antimicrobial susceptibility testing were carried out by VITEK2 Compact (bioMerieux).

RESULTS

There was not a substantial difference in the etiology of hip and knee PJI: staphylococci were the most frequently isolated bacteria in both groups, followed by Enterobacteriaceae and Propionibacterium acnes. Staphylococci showed a high rate of methicillin resistance (144 of 341) and a worrying frequency of isolates were resistant to teicoplanin (9%). Only 8.3% of Enterobacteriaceae produced extended-spectrum beta-lactamases, whereas the rate of carbapenemase-producing bacteria was not significant.

CONCLUSION

We observed similar etiology of hip and knee PJIs. Nevertheless, bacteria isolated from knee showed higher resistance rates to glycopeptides and fluoroquinolones when compared with those isolated from the hip. The reason for this difference remains to be elucidated in future studies.

Orthopedic infections caused by obligatory anaerobic Gram-negative rods: report of two cases

Anaerobic bone and joint infections are uncommon, although the number of anaerobic infections is presumably underestimated because of difficulties with isolation and identification of obligate anaerobes. This study describes two cases of complicated Bacteroides fragilis peri-implant infection of the lumbar spine, infection of the hip and osteomyelitis. Bacteria were identified with the use of a mass spectrometer, VITEK MS system. Drug susceptibility was performed with the use of E-test. The EUCAST breakpoints were used for interpretation with B. fragilis ATCC 25285 as a control. In the two described cases clinical samples were collected for microbiological examination intraoperatively and simultaneously empirical treatment was applied. B. fragilis was isolated in monoculture or in a combination with other bacteria. The treatment was continued according to the susceptibility tests. In a case one clindamycin failure was observed and clindamycin resistance of the isolate was likely due to inadequate time of therapy. Difficulties in collecting an adequate samples and culturing anaerobic bacteria cause that not all infections are properly recognized. In a successful therapy, identification and determination of the susceptibility of the pathogen are essential as well as an appropriate surgical debridement.

Multicenter Investigation of the Micro-Organisms Involved in Penile Prosthesis Infection: An Analysis of the Efficacy of the AUA and EAU Guidelines for Penile Prosthesis Prophylaxis

INTRODUCTION

Penile prosthesis infections remain challenging despite advancements in surgical technique, device improvements, and adoption of antibiotic prophylaxis guidelines.

AIM

To investigate penile prosthesis infection microbiology to consider which changes in practice could decrease infection rates, to evaluate current antibiotic prophylaxis guidelines, and to develop a proposed algorithm for penile prosthesis infections.

METHODS

This retrospective institutional review board-exempt multi-institutional study from 25 centers reviewed intraoperative cultures obtained at explantation or Mulcahy salvage of infected three-piece inflatable penile prostheses (IPPs). Antibiotic usage was recorded at implantation, admission for infection, and explantation or salvage surgery. Cultures were obtained from purulent material in the implant space and from the biofilm on the device.

MAIN OUTCOME MEASURES

Intraoperative culture data from infected IPPs.

RESULTS

Two hundred twenty-seven intraoperative cultures (2002-2016) were obtained at salvage or explantation. No culture growth occurred in 33% of cases and gram-positive and gram-negative organisms were found in 73% and 39% of positive cultures, respectively. Candida species (11.1%), anaerobes (10.5%) and methicillin-resistant Staphylococcus aureus (9.2%) constituted nearly one third of 153 positive cultures. Multi-organism infections occurred in 25% of positive cultures. Antibiotic regimens at initial implantation were generally consistent with American Urological Association (AUA) and European Association of Urology (EAU) guidelines. However, the micro-organisms identified in this study were covered by these guidelines in only 62% to 86% of cases. Antibiotic selection at admissions for infection and salvage or explantation varied widely compared with those at IPP implantation.

CONCLUSION

This study documents a high incidence of anaerobic, Candida, and methicillin-resistant S aureus infections. In addition, approximately one third of infected penile prosthesis cases had negative cultures. Micro-organisms identified in this study were not covered by the AUA and EAU antibiotic guidelines in at least 14% to 38% of cases. These findings suggest broadening antibiotic prophylaxis guidelines and creating a management algorithm for IPP infections might lower infection rates and improve salvage success. Gross MS, Phillips EA, Carrasquillo RJ, et al. Multicenter Investigation of the Micro-Organisms Involved in Penile Prosthesis Infection: An Analysis of the Efficacy of the AUA and EAU Guidelines for Penile Prosthesis Prophylaxis. J Sex Med 2017;14:455-463.

Propionibacterium acnes: Time-to-Positivity in Standard Bacterial Culture From Different Anatomical Sites

BACKGROUND

Propionibacterium acnes infections are likely under-recognized and underreported. This is partly because of low clinical suspicion, perceived non-pathogenicity, or lack of adequate culture incubation time. We conducted a study to assess the optimal incubation period to recover P. acnes from specimens acquired during the workup of suspected clinical infections.

METHODS

A 5-year retrospective chart review was conducted between January 2010 and December 2014 at a single tertiary-care hospital. All patient cases from which P. acnes was recovered were included for analysis. Source of infection, antibiotic use, and culture time-to-positivity (TTP) were recorded.

RESULTS

Implanted devices comprised the single most common source of P. acnes infection. In the majority of cases, P. acnes was the only organism identified. The mean incubation TTP for all isolates was 5.73 days.

CONCLUSIONS

Standard 5-day culture incubation periods are insufficient to recover P. acnes. As a result, P. acnes is likely a much more common etiology of a variety of clinical infections than previously reported.

Propionibacterium acnes Susceptibility and Correlation with Hemolytic Phenotype

BACKGROUND

Many studies have noted an increase in the number of recognized cases of invasive infections due to Propionibacterium acnes, especially after shoulder replacement surgery. The increase in the number of recognized cases of P. acnes, a nonspore-forming, anaerobic, Gram-positive organism, appears due to both an increase in the number of shoulder operations being performed and more specimens being sent for anaerobic cultures. Nevertheless, the optimal surgical and antibiotic management of P. acnes remains controversial.

METHODS

We tested the susceptibility of 106 P. acnes strains from sterile body sites collected at the Erie County Medical Center between 2012 and 2015, using Etest gradient antibiotic strips.

RESULTS

P. acnes is very susceptible to the penicillins and the first-generation cephalosporins. We noted an association between hemolytic phenotype on Brucella Blood Agar and clindamycin resistance.

CONCLUSIONS

Antimicrobial susceptibility testing of P. acnes should no longer just be confined to the research laboratory but expanded and incorporated into routine microbiological evaluation of P. acnes. This would improve patient care as well as help clarify the relationship between hemolysis and clindamycin resistance.

Clinical features of anaerobic orthopaedic infections

Some patient populations and types of orthopaedic surgery could be at particular risk for anaerobic infections. In this retrospective cohort study of operated adult patients with infections from 2004 to 2014, we assessed obligate anaerobes and considered first clinical infection episodes. Anaerobes, isolated from intra-operative samples, were identified in 2.4% of 2740 surgical procedures, of which half (33/65; 51%) were anaerobic monomicrobial infections. Propionibacterium acnes, a penicillin and vancomycin susceptible pathogen, was the predominantly isolated anaerobe. By multivariate analysis, the presence of fracture fixation plates was the variable most strongly associated with anaerobic infection (odds ratio: 2.1, 95% CI: 1.3-3.5). Anaerobes were also associated with spondylodesis and polymicrobial infections. In contrast, it revealed less likely in native bone or prosthetic joint infections and was not related to prior antibiotic use. In conclusion, obligate anaerobes in our case series of orthopaedic infections were rare, and mostly encountered in infections related to trauma with open-fracture fixation devices rather than clean surgical site infection. Anaerobes were often co-pathogens, and cultures most frequently recovered P. acnes. These observations thus do not support changes in current practices such as broader anaerobe coverage for perioperative prophylaxis.

Prosthetic Device Infections

The immunocompromised host is a particularly vulnerable population in whom routine and unusual infections can easily and frequently occur. Prosthetic devices are commonly used in these patients and the infections associated with those devices present a number of challenges for both the microbiologist and the clinician. Biofilms play a major role in device-related infections, which may contribute to failed attempts to recover organisms from routine culture methods. Moreover, device-related microorganisms can be difficult to eradicate by antibiotic therapy alone. Changes in clinical practice and advances in laboratory diagnostics have provided significant improvements in the detection and accurate diagnosis of device-related infections. Disruption of the bacterial biofilm plays an essential role in recovering the causative agent in culture. Various culture and nucleic acid amplification techniques are more accurate to guide directed treatment regimens. This chapter reviews the performance characteristics of currently available diagnostic assays and summarizes published guidelines, where available, for addressing suspected infected prosthetic devices.

Microbiological Diagnosis of Implant-Related Infections: Scientific Evidence and Cost/Benefit Analysis of Routine Antibiofilm Processing

Prosthetic joint infection is one of the most severe complication following joint arthroplasty, producing a significant worsening of patient's quality of life. Management of PJIs requires extended courses of antimicrobial therapy, multiple surgical interventions and prolonged hospital stay, with a consequent economic burden, which is thought to markedly increase in the next years due to the expected burden in total joint arthroplasties. The present review summarizes the present knowledge on microbiological diagnosis of prosthetic joint infections, focusing on aethiological agents and discussing pros and cons of the available strategies for their diagnosis.Intra-operative clinical diagnosis and pathogen identification is considered the diagnostic benchmark, however the presence of bacterial biofilm makes pathogen detection with traditional microbiological techniques highly ineffective. Diagnosis of PJIs is a rather complex challenge for orthopedics and requires a strict collaboration between different specialists: orthopaedics, infectivologists, microbiologists, pathologists and radiologists. Diagnostic criteria have been described by national and international association and scientific societies. Clinicians should be trained on how to use it, but more importantly they should know potential and limitation of the available tests in order to use them appropriately.