Molecular detection of transcriptionally active bacteria from failed prosthetic hip joints removed during revision arthroplasty

Improved identification of polymicrobial infection in total knee arthroplasty through sonicate fluid cultures

INTRODUCTION

Periprosthetic joint infection (PJI) is the leading cause for early failure of total knee arthroplasty (TKA). An insufficient diagnosis of the involved bacterial species can be a possible cause for this high failure rate. Sonicate fluid cultures (SFC) have been shown to increase the detection rate of PJI in comparison to the use of conventional microbiological methods. The hypothesis of this study is that sonication will improve not only the detection rate of PJI, but also the detection rate of polymicrobial infection in patients with TKA revision surgery.

MATERIALS AND METHODS

109 patients, undergoing TKA revision surgery, were enrolled in this prospective cohort study and received a synovial aspiration, intraoperative tissue cultures, histological sampling of the periprosthetic membrane (PM), and sonication of the explanted endoprosthesis. A PJI was defined according to the following criteria: presence of intraarticular pus or a sinus tract, positive isolation of the same bacterial species in ≥2 microbiological samples or a PM indicative of infection.

RESULTS

31 patients had a defined PJI according to the above-mentioned criteria. SFC achieved the highest sensitivity (74 %) of all microbiological methods. The PM achieved a sensitivity of 87 %. When the results of the SFC and the PM were combined, it was possible to further increase the sensitivity to 94 %. The utilization of SFC doubled the number of polymicrobial bacterial isolations in our patient collective. There were 12 cases of polymicrobial bacterial isolations, six were detectable through conventional microbiological methods, four were detectable through SFC and two were identifiable as polymicrobial through the isolation of an additional bacterial species in the SFC.

CONCLUSIONS

In our study, SFC were the most sensitive microbiological method and were surpassed only by the histology. The use of SFC doubled the detection rate of polymicrobial isolations, which would be missed with conventional microbiological methods alone.

Enrichment of bacteria samples by centrifugation improves the diagnosis of orthopaedics-related infections via real-time PCR amplification of the bacterial methicillin-resistance gene

Background

To effectively treat orthopaedic infections by methicillin-resistant strains, an early diagnosis is necessary. Bacterial cultures and real-time polymerase chain reaction (PCR) have been used to define methicillin-resistant staphylococci. However, even when patients display clinical signs of infections, bacterial culture and real-time PCR often cannot confirm infection. The aim of this study was to prospectively compare the utility of real-time PCR for the mecA gene detection following centrifugation of human samples with suspected orthopaedic infections.

Results

In addition to the conventional real-time PCR method, we performed real-time PCR following centrifugation of the sample at 4,830×g for 10 min in a modified real-time PCR (M-PCR) method. We suspended cultured methicillin-resistant Staphylococcus aureus and generated standard dilution series for in vitro experiments. The in vitro detection sensitivity of the M-PCR method was approximately 5.06 times higher than that of the conventional real-time PCR method. We performed bacterial culture, pathological examination, real-time PCR, and M-PCR to examine the infectious fluids and tissues obtained from 36 surgical patients at our hospital. Of these, 20 patients who had undergone primary total hip arthroplasty were enrolled as negative controls. In addition, 15 patients were examined who were clinically confirmed to have an infection, including periprosthetic joint infection (eight patients), pyogenic spondylitis (two patients), infectious pseudoarthrosis (two patients), and after spine surgery (three patients). In one sample from a patient who developed infectious pseudoarthrosis and two samples from surgical site infections after spine surgery, the mecA gene was detected only by the M-PCR method. In one patient with infectious pseudoarthrosis, one patient with infection after arthroplasty, and two patients with purulent spondylitis, the detection sensitivity of the M-PCR method was increased compared with PCR (clinical sample average: 411.6 times).

Conclusions

These findings suggest that the M-PCR method is useful to detect methicillin-resistant strains infections. In addition, the centrifugation process only takes 10 min longer than conventional real-time PCR methods. We believe that the M-PCR method could be clinically useful to detect orthopaedic infections caused by methicillin-resistant strains.

Electronic supplementary material

The online version of this article (doi:10.1186/s13104-015-1180-2) contains supplementary material, which is available to authorized users.

Culture-negative periprosthetic joint infection

➤ Negative results on culture still pose a real challenge in the diagnosis of periprosthetic joint infection.➤ There are numerous reasons for the inability to isolate the infecting organism from the affected joint, the most important of which is the administration of antibiotics prior to obtaining culture samples.➤ For patients suspected of having a periprosthetic joint infection, antibiotics should not be given until the diagnosis is confirmed or aspiration of the joint should be delayed for at least two weeks after the last dose of antibiotics.➤ Other strategies that can be used to enhance the likelihood of obtaining a positive result on culture include expeditious transport of culture samples, placement of a tissue or fluid sample in the appropriate medium, implant sonication, and prolonging the incubation period of the samples to two or three weeks.➤ In patients in whom the prerevision aspiration has not yielded an infecting organism, yet the clinical picture is consistent with periprosthetic joint infection, a minimum of three to five tissue culture samples are recommended at the time of revision surgery.➤ Biomarkers and molecular techniques, such as polymerase chain reaction identification of bacterial DNA, may play an increasing role in the future in the diagnosis of periprosthetic joint infection, when standardized techniques have not identified an infecting organism.

Biofilm-degrading enzymes from Lysobacter gummosus

Biofilm-degrading enzymes could be used for the gentle cleaning of industrial and medical devices and the manufacture of biofilm-resistant materials. We therefore investigated 20 species and strains of the bacterial genus Lysobacter for their ability to degrade experimental biofilms formed by Staphylococcus epidermidis, a common nosocomial pathogen typically associated with device-related infections. The highest biofilm-degradation activity was achieved by L. gummosus. The corresponding enzymes were identified by sequencing the L. gummosus genome. Partial purification of the biofilm-degrading activity from an extract of extracellular material followed by peptide mass fingerprinting resulted in the identification of two peptidases (α-lytic protease and β-lytic metalloendopeptidase) that were predicted to degrade bacterial cell walls. In addition, we identified two isoforms of a lysyl endopeptidase and an enzyme similar to metalloproteases from Vibrio spp. Potential peptidoglycan-binding C-terminal fragments of two OmpA-like proteins also co-purified with the biofilm-degrading activity. The L. gummosus genome was found to encode five isoenzymes of α-lytic protease and three isoenzymes of lysyl endopeptidase. These results indicated that the extracellular digestion of biofilms by L. gummosus depends on multiple bacteriolytic and proteolytic enzymes, which could now be exploited for biofilm control.

Conventional and molecular diagnostic strategies for prosthetic joint infections

An accurate diagnosis of prosthetic joint infection (PJI) is the mainstay for an optimized clinical management. This review analyzes different diagnostic strategies of PJI, with special emphasis on molecular diagnostic tools and their current and future applications. Until now, the culture of periprosthetic tissues has been considered the gold standard for the diagnosis of PJI. However, sonication of the implant increases the sensitivity of those cultures and is being increasingly adopted by many centers. Molecular diagnostic methods compared with intraoperative tissue culture, especially if combined with sonication, have a higher sensitivity, a faster turnaround time and are not influenced by previous antimicrobial therapy. However, they still lack a system for detection of antimicrobial susceptibility, which is crucial for an optimized and less toxic therapy of PJI. More studies are needed to assess the clinical value of these methods and their cost-effectiveness.

Evaluation of the bacterial distribution within the biofilm by denaturing gradient gel electrophoresis in the rat model of urinary catheters

PURPOSE

Most nosocomial urinary tract infections are related to urinary catheters and their biofilm. For the research in this province, animal models are needed to explain the host-pathogen interactions and have an advantage in controlling external interference. This study investigated the validity of the denaturing gradient gel electrophoresis (DGGE) technique for identification of bacteria in a rat model of urinary catheter biofilm.

METHODS

After cutting with aseptic technique, the 24-gauge polyurethane IV catheter was placed in the female rat bladder through the urethra. The catheters were kept in the bladder for 2, 4, or 6 weeks for each group. The genomic DNA was isolated from harvested biofilm of the extracted catheter, and DGGE was performed. The band patterns of DGGE results were analysed, and the sequences were compared using the BLAST from the NCBI.

RESULTS

The results show that Pseudomonas aerusinosa, Escherichia coli, Enterococcus spp., and Corynebacterium sp. were the dominant bacterial species, regardless of the indwelling periods, and other species of bacteria, including Burkholderia and Achromobacter, were identified. The changes in bacterial distribution for the different indwelling periods were non-specific.

CONCLUSIONS

This study using rat model of urinary catheter suggests that DGGE is a useful method in the analysis of the bacterial community in biofilms. Molecular techniques, including DGGE, are valuable to identify fastidious bacteria in the urinary catheter biofilm. This study may be used as fundamental data for studies involving human materials hereafter.

PCR-hybridization after sonication improves diagnosis of implant-related infection

PURPOSE

We wanted to improve the diagnosis of implant-related infection using molecular biological techniques after sonication.

METHODS

We studied 258 retrieved implant components (185 prosthetic implants and 73 osteosynthesis implants) from 126 patients. 47 patients had a clinical diagnosis of infection (108 components) and 79 patients did not (150 components). The fluids from sonication of retrieved implants were tested in culture and were also analyzed using a modified commercial PCR kit for detection of Gram-positive and Gram-negative bacteria (GenoType BC; Hain Lifescience) after extraction of the DNA.

RESULTS

38 of 47 patients with a clinical diagnosis of infection were also diagnosed as being infected using culture and/or PCR (35 by culture alone). Also, 24 patients of the 79 cases with no clinical diagnosis of infection were identified microbiologically as being infected (4 by culture, 16 by PCR, and 4 by both culture and PCR). Comparing culture and PCR, positive culture results were obtained in 28 of the 79 patients and positive PCR results were obtained in 35. There were 21 discordant results in patients who were originally clinically diagnosed as being infected and 28 discordant results in patients who had no clinical diagnosis of infection.

INTERPRETATION

For prosthetic joint infections and relative to culture, molecular detection can increase (by one tenth) the number of patients diagnosed as having an infection. Positive results from patients who have no clinical diagnosis of infection must be interpreted carefully.