Prospective Analysis of a Sterile, Semi-automated Tissue Biopsy Homogenization Method in the Diagnosis of Prosthetic Joint Infections

Future directions for early detection of fracture related infections

Introduction

Fracture related infection (FRI) refers to pathogens infecting a fracture site and hence impeding fracture healing. It is a significant complication that carries substantial disease burden and socio-economic costs, but has had limited scientific development. Hence, this paper will review the existing strategies for early detection of FRI, in the form of serum markers, molecular diagnostics and imaging modalities, and further discuss potential future directions for improved detection of FRI.

Existing Strategies for Diagnosis of FRI

The Anti-infection Global Expert Committee (AIGEC) developed a consensus definition for FRI in 2017, which includes confirmatory and suggestive criteria for diagnosis of FRI. Existing strategies for diagnosis include clinical, laboratory, histopathological, microbiological and radiological investigations.

Future Directions for Early Detection of FRI

With increasing recognition of FRI, early detection is crucial for early treatment to be enforced. We have identified potential areas for future development in diagnostics for early detection of FRI, which are discussed in this manuscript. They include inflammatory cytokines, serum calcium levels, platelet count, improved management of histopathological and microbiological specimens, metagenomics, wound biomarkers, gut microbiota analysis, and novel imaging technologies.

Rapid high-throughput processing of tissue samples for microbiological diagnosis of periprosthetic joint infections using bead-beating homogenization

Enrichment of periprosthetic tissue samples in blood culture bottles (BCBs) for microbiological diagnosis of periprosthetic joint infections (PJI) is more reliable than the use of an enrichment broth. Nevertheless, the extremely time-consuming homogenization of the samples for BCB processing has so far limited its use, especially in high-throughput settings. We aimed to establish a highly scalable homogenization process of tissue samples for long-term incubation in BCBs. A protocol for homogenization of tissue samples using bead beating was established and validated. In a second step, the use of the homogenate for enrichment in BCBs was compared to the use of thioglycolate broth (TB) in terms of diagnostic accuracy using clinical tissue samples from 150 patients with suspected PJI. Among 150 analyzed samples, 35 samples met the microbiological criteria for PJI. Using BCB, 32 of 35 (91.4%) PJI were detected compared to 30 of 35 (85.7%) by TB. The use of BCB had a lower secondary contamination rate (2/115; 1.7% vs 4/115; 3.5%) but the trend was not significant due to low numbers of samples (P = 0.39). The time to process a batch of 12 samples using the established homogenization method was 23 ± 5 min (n = 10 batches). We established and validated a homogenization workflow that achieves the highest sensitivity in the microbiological diagnostic of PJI. The enrichment of the tissue homogenate in BCBs showed equally good results as the use of enrichment broth and allows semi-automated high-throughput processing while demonstrating lower contamination rates in our study.

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.

What is the best technic to dislodge Staphylococcus epidermidis biofilm on medical implants?

Background

Bacterial biofilm can occur on all medical implanted devices and lead to infection and/or dysfunction of the device.

In this study, artificial biofilm was formed on four different medical implants (silicone, piccline, peripheral venous catheter and endotracheal tube) of interest for our daily clinical and/or research practice. We investigated the best conventional technic to dislodge the biofilm on the implants and quantified the number of bacteria. Staphylococcus epidermidis previously isolated from a breast implant capsular contracture on a patient in the university hospital of Dijon was selected for its ability to produce biofilm on the implants. Different technics (sonication, Digest-EUR®, mechanized bead mill, combination of sonication plus Digest-EUR®) were tested and compared to detach the biofilm before quantifying viable bacteria by colony counting.

Results

For all treatments, the optical and scanning electron microscope images showed substantial less biofilm biomass remaining on the silicone implant compared to non-treated implant.

This study demonstrated that the US procedure was statistically superior to the other physical treatment: beads, Digest-EUR® alone and Digest-EUR® + US (p < 0.001) for the flexible materials (picc-line, PIV, and silicone). The number of bacteria released by the US is significantly higher with a difference of 1 log on each material. The result for a rigid endotracheal tube were different with superiority for the chemical treatment dithiothreitol: Digest-EUR®. Surprisingly the combination of the US plus Digest-EUR® treatment was consistently inferior for the four materials.

Conclusions

Depending on the materials used, the biofilm dislodging technique must be adapted. The US procedure was the best technic to dislodge S. epidermidis biofilm on silicone, piccline, peripheral venous catheter but not endotracheal tube. This suggested that scientists should compare themselves different methods before designing a protocol of biofilm study on a given material.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02606-x.

Pre-processing tissue specimens with a tissue homogenizer: clinical and microbiological evaluation

BACKGROUND

Tissues are valuable specimens in diagnostic microbiology because they are often obtained by invasive methods, and effort should thus be taken to maximize microbiological yield. The objective of this study was to evaluate the added value of using tissue pre-processing (tissue homogenizer instrument gentleMACS Dissociator) in detecting microorganisms responsible for infections.

METHODS

We included 104 randomly collected tissue samples, 41 (39.4 %) bones and 63 (60.6 %) soft tissues, many of those (42/104 (40.4 %)) were of periprosthetic origins. We compared the agreement between pre-processing tissues using tissue homogenizer with routine microbiology diagnostic procedure, and we calculated the performance of these methods when clinical infections were used as reference standard.

RESULTS

There was no significant difference between the two methods (McNemar test, p = 0.3). Among the positive culture using both methods (n = 62), 61 (98.4 %) showed at least one similar microorganism. Exactly similar microorganisms were found in 42/62 (67.7 %) of the samples. From the included tissues, 55/ 104 (52.9 %) were deemed as infected. We found that the sensitivity of homogenized tissue procedure was lower (83.6 %) than when tissue was processed using tissue homogenizer (89.1 %). Sub-analysis on periprosthetic tissues and soft or bone tissues showed comparable results.

CONCLUSIONS

The added value of GentleMACS Dissociator tissue homogenizer is limited in comparison to routine tissue processing.