Sonicate fluid inoculated into blood culture bottles does not improve diagnosis of periprosthetic joint infection caused by anaerobes. A retrospective analysis

Direct Prosthetic Joint Infection Diagnosis from Sonication Fluid Inoculated in Blood Culture Bottles by Direct MALDI-TOF Mass Spectrometry

An accurate and fast microbiological diagnosis is key for a proper management and results when facing prosthetic joint infection (PJI). The purpose of this study is to assess the role of direct Matrix-assisted laser desorption ionization time of flight (MALDI-TOF) mass spectrometry (MS) for early identification of the pathogens causing PJI from sonication fluid inoculated in blood culture bottles (BCB-SF). This prospective multicentric study included 107 consecutive patients from February 2016 to February 2017. Among them, 71 prosthetic joint revision surgeries were undergone for aseptic and 36 for septic reasons. Prostheses were sonicated and the resulting fluid inoculated into blood culture bottles, regardless the suspicion for infection. We assessed the diagnostic performance of direct MALDI-TOF MS identification of the pathogens in BCB-SF and compared it with periprosthetic tissue and conventional sonication fluid cultures. The sensitivity of direct MALDI-TOF MS of BCB-SF (69%) was higher compared to conventional sonication fluid (69% vs. 64%, p > 0.05) or intraoperative tissue cultures (69% vs. 53%, p = 0.04), especially for patients receiving antimicrobial treatment. This approach also reduced the time for identification but the specificity was compromised (100% vs. 94%) and polymicrobial infections were missed. In conclusion, BCB-SF improves the sensitivity and reduces the time of PJI diagnosis when used in combination with conventional cultures under strict sterility conditions.

Evaluation of two different semi-automated homogenization techniques in microbiological diagnosis of periprosthetic joint infection: disperser vs. bead milling method

Background

In microbiological diagnosis of periprosthetic joint infection (PJI) there is no consensus regarding the most suitable and optimal number of specimens to be cultured or the most effective technique of tissue processing. This comparative study analysed the accuracy of two semi-automated homogenization methods with special focus on the volume and exact origin of each sample.

Methods

We investigated a total of 722 periprosthetic tissue samples. PJI was defined according to the new scoring system for preoperative and intraoperative criteria. We compared the performance of our routinely used single tissue processing by disposable high-frequency disperser with the bead milling method.

Results

Eighty patients were included. Among forty classified PJIs, 34 patients yielded positive culture results. In 23 cases (68%) exact concordant results were generated with both techniques. However, in seven cases (20%) processing by the disperser and in four cases (12%) by bead milling provided additional positive samples, but without significant difference since the major definition criteria were met in all cases. The percentage of positive results was influenced by the volume and origin of the tissue samples. Results for small tissue samples tended to be better using the bead milling method. This might lead to improved preoperative arthroscopic diagnosis, as the volume of biopsies is generally limited. Six patients had negative results due to previous antimicrobial therapy. Forty other patients were classified as aseptic failures. Neither procedure resulted in any contamination.

Conclusion

Both methods enable reliable processing of tissue samples for diagnosis of PJI and are suitable for routine use.

Identification of Peptoniphilus harei From Blood Cultures in an Infected Aortic Aneurysm Patient: Case Report and Review Published Literature

Gram-positive anaerobic cocci (GPAC) are a commensal part of human flora but are also opportunistic pathogens. This is possibly the first study to report a case of Peptoniphilus harei bacteremia in an abdominal aortic aneurysm (AAA) patient. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) failed to identify the isolate and molecular analysis confirmed it as P. harei. A comprehensive literature review revealed that P. harei is an emergent pathogen. This study serves as a reminder for practicing clinicians to include anaerobic blood cultures as part of their blood culture procedures; this is particularly important situations with a high level of suspicion of infection factors in some noninfectious diseases, as mentioned in this publication. Clinical microbiologists should be aware that the pathogenic potential of GPAC can be greatly underestimated leading to incorrect diagnosis on using only one method for pathogen identification. Upgradation and correction of the MALDI-TOF MS databases is recommended to provide reliable and rapid identification of GPAC at species level in medical diagnostic microbiology laboratories.

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.

Micromonas micros Infection of a Prosthetic Hip Joint: A Case Report and Review of the Literature

Micromonas micros is an oral anaerobic Gram-positive coccus and is a commensal of the mouth, and it is rarely isolated in prosthetic joint infections (PJIs) and even less frequently related to a preceding dental procedure with eventual hematogenous seeding of the prosthetic joint. Here, we present a case of a 56-year-old male with a prosthetic hip joint who developed Micromonas micros prosthetic hip joint infection with symptoms starting a few days after a dental procedure and not having received periprocedural antibiotic prophylaxis. He recovered well with surgical intervention and antimicrobial therapy. We conducted a literature review of prosthetic hip joint infections caused by Micromonas micros as well as briefly discuss current guidelines on antibiotic prophylaxis in patients with prosthetic joints undergoing dental procedures and some knowledge gaps.

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.

Microbiological diagnosis of polymicrobial periprosthetic joint infection revealed superiority of investigated tissue samples compared to sonicate fluid generated from the implant surface

OBJECTIVES

In the microbiological diagnosis of periprosthetic joint infection (PJI), there is much discussion about the methodology of obtaining proper specimens, the processing technique, and suitable culture media. This retrospective study was conducted to analyse the accuracy of our culture techniques.

METHODS

Tissue samples and components from 258 patients after revision arthroplasty of the hip, knee, and shoulder were investigated, and the results of tissue cultures (TC) were compared to those of sonicate fluid cultures (SFC). Furthermore, an evaluation was performed of the influence of different culture media on the detection rate.

RESULTS

PJI was confirmed in 186 patients. The overall sensitivity of TC was no different to that of SFC (91.3% vs 90.8%, P = 1). In 153 cases (82.3%), TC and SFC showed concordant positive results. Results were discordant in 33 cases (17.7%). When differentiated according to the type of infection, TC showed significantly better results than SFC in detecting polymicrobial infections (97.0% vs 67.0%, P = 0.004). There were also significant differences between the culture media regarding the yield of microorganisms.

CONCLUSIONS

TC was more effective in detecting co-infections. The best results were obtained using both TC and SFC. The choice of culture media has a significant influence on the quality of results.