Demonstration of Bacillus cereus in orthopaedic-implant-related infection with use of a multi-primer polymerase chain reaction-mass spectrometric assay: report of two cases

A Response Surface Methodological Approach for Large-Scale Production of Antibacterials from Lactiplantibacillus plantarum with Potential Utility against Foodborne and Orthopedic Infections

A variety of bacteria, including beneficial probiotic lactobacilli, produce antibacterials to kill competing bacteria. Lactobacilli secrete antimicrobial peptides (AMPs) called bacteriocins and organic acids. In the food industry, bacteriocins, but even whole cell-free supernatants, are becoming more and more important as bio-preservatives, while, in orthopedics, bacteriocins are introducing new perspectives in biomaterials technologies for anti-infective surfaces. Studies are focusing on Lactiplantibacillus plantarum (previously known as Lactobacillus plantarum). L. plantarum exhibits great phenotypic versatility, which enhances the chances for its industrial exploitation. Importantly, more than other lactobacilli, it relies on AMPs for its antibacterial activity. In this study, Response Surface Methodology (RSM) through a Box-Behnken experimental design was used to estimate the optimal conditions for the production of antibacterials by L. plantarum. A temperature of 35 °C, pH 6.5, and an incubation time of 48 h provided the highest concentration of antibacterials. The initial pH was the main factor influencing the production of antibacterials, at 95% confidence level. Thanks to RSM, the titer of antibacterials increased more than 10-fold, this result being markedly higher than those obtained in the very few studies that have so far used similar statistical methodologies. The Box-Behnken design turned out to be a valid model to satisfactorily plan a large-scale production of antibacterials from L. plantarum.

Promising applications of D-amino acids in periprosthetic joint infection

Due to the rise in our aging population, a disproportionate demand for total joint arthroplasty (TJA) in the elderly is forecast. Periprosthetic joint infection (PJI) represents one of the most challenging complications that can occur following TJA, and as the number of primary and revision TJAs continues to rise, an increasing PJI burden is projected. Despite advances in operating room sterility, antiseptic protocols, and surgical techniques, approaches to prevent and treat PJI remain difficult, primarily due to the formation of microbial biofilms. This difficulty motivates researchers to continue searching for an effective antimicrobial strategy. The dextrorotatory-isoforms of amino acids (D-AAs) are essential components of peptidoglycan within the bacterial cell wall, providing strength and structural integrity in a diverse range of species. Among many tasks, D-AAs regulate cell morphology, spore germination, and bacterial survival, evasion, subversion, and adhesion in the host immune system. When administered exogenously, accumulating data have demonstrated that D-AAs play a pivotal role against bacterial adhesion to abiotic surfaces and subsequent biofilm formation; furthermore, D-AAs have substantial efficacy in promoting biofilm disassembly. This presents D-AAs as promising and novel targets for future therapeutic approaches. Despite their emerging antibacterial efficacy, their role in disrupting PJI biofilm formation, the disassembly of established TJA biofilm, and the host bone tissue response remains largely unexplored. This review aims to examine the role of D-AAs in the context of TJAs. Data to date suggest that D-AA bioengineering may serve as a promising future strategy in the prevention and treatment of PJI.

Beyond the pan-genome: current perspectives on the functional and practical outcomes of the distributed genome hypothesis

The principle of monoclonality with regard to bacterial infections was considered immutable prior to 30 years ago. This view, espoused by Koch for acute infections, has proven inadequate regarding chronic infections as persistence requires multiple forms of heterogeneity among the bacterial population. This understanding of bacterial plurality emerged from a synthesis of what-were-then novel technologies in molecular biology and imaging science. These technologies demonstrated that bacteria have complex life cycles, polymicrobial ecologies, and evolve in situ via the horizontal exchange of genic characters. Thus, there is an ongoing generation of diversity during infection that results in far more highly complex microbial communities than previously envisioned. This perspective is based on the fundamental tenet that the bacteria within an infecting population display genotypic diversity, including gene possession differences, which result from horizontal gene transfer mechanisms including transformation, conjugation, and transduction. This understanding is embodied in the concepts of the supragenome/pan-genome and the distributed genome hypothesis (DGH). These paradigms have fostered multiple researches in diverse areas of bacterial ecology including host-bacterial interactions covering the gamut of symbiotic relationships including mutualism, commensalism, and parasitism. With regard to the human host, within each of these symbiotic relationships all bacterial species possess attributes that contribute to colonization and persistence; those species/strains that are pathogenic also encode traits for invasion and metastases. Herein we provide an update on our understanding of bacterial plurality and discuss potential applications in diagnostics, therapeutics, and vaccinology based on perspectives provided by the DGH with regard to the evolution of pathogenicity.

Post-procedural Bacillus cereus septic arthritis in a patient with systemic lupus erythematosus

INTRODUCTION

Bacillus species are often considered as contaminants when cultured from clinical samples. Bacillus cereus may be a pathogen in certain circumstances and is known to cause musculoskeletal infections. This report aims to educate clinicians and clinical microbiology laboratories on B. cereus musculoskeletal infections and to heighten awareness that Bacillus species should not always be dismissed as contaminants.

CASE PRESENTATION

We report the case of a patient who presented to a tertiary hospital in Pretoria, South Africa, in November 2018 with B. cereus septic arthritis and underlying systemic lupus erythematosus (SLE). The isolate would otherwise have been dismissed as a contaminant had it not been for the crucial interaction between the laboratory and the treating clinicians. To our knowledge, this is the first case report of septic arthritis caused by B. cereus in an SLE patient where the organism was cultured from the joint specimen. Identification of the organism was performed using matrix-assisted laser desorption/ionisation mass spectrometry.

MANAGEMENT AND OUTCOME

Definitive treatment was with intravenous vancomycin, continued for four weeks, in addition to arthroscopy and management of the underlying SLE. The patient had a good clinical outcome and regained full mobility.

CONCLUSION

Musculoskeletal infections, specifically septic arthritis caused by B. cereus, are exceedingly rare infections. Immune suppression, trauma, prosthetic implants and invasive procedures are important risk factors for B. cereus musculoskeletal infections. Close collaboration with a multi-disciplinary team approach will effect the best outcome for complicated patients with B. cereus infections.

Bacterial Deoxyribonucleic Acid Is Often Present in Failed Revision Anterior Cruciate Ligament Reconstructions

PURPOSE

To determine whether bacterial DNA will be detectable by polymerase chain reaction (PCR) in torn graft tissue at the time of revision anterior cruciate ligament reconstruction (ACLR).

METHODS

A total of 31 consecutive revision ACLR cases from 1 center from 2014-2016 were recruited. No patients had clinical signs of infection on presentation. Torn graft tissue was obtained in revision cases and subjected to clinical culture and PCR analysis with a universal bacterial primer. Fluorescence microscopy was used to confirm the presence of a biofilm. We obtained negative control samples of water open to air on the field and excess primary ACLR graft tissue, as well as torn native ligament, to evaluate for PCR positivity due to environmental contamination.

RESULTS

Clinical cultures were positive (coagulase-negative Staphylococcus) in 1 revision case (3%, 1 of 31). Bacterial DNA was detectable in most revision ACLR cases (87.0%, 27 of 31), and there was a low rate of PCR positivity in negative control samples of water open to air (0%, 0 of 3), excess primary ACLR graft tissue after passage (20%, 1 of 5), or native torn ligament (20%, 1 of 5). Bacterial biofilm presence on failed graft tissue as well as monofilament suture was visually confirmed with fluorescence microscopy.

CONCLUSIONS

Bacterial DNA is frequently present in failed ACLR grafts, with high rates of DNA detection by PCR but low culture positivity.

LEVEL OF EVIDENCE

Level IV, case series.

Comparing culture and molecular methods for the identification of microorganisms involved in necrotizing soft tissue infections

Background

Necrotizing soft tissue infections (NSTIs) are a group of infections affecting all soft tissues. NSTI involves necrosis of the afflicted tissue and is potentially life threatening due to major and rapid destruction of tissue, which often leads to septic shock and organ failure. The gold standard for identification of pathogens is culture; however molecular methods for identification of microorganisms may provide a more rapid result and may be able to identify additional microorganisms that are not detected by culture.

Methods

In this study, tissue samples (n = 20) obtained after debridement of 10 patients with NSTI were analyzed by standard culture, fluorescence in situ hybridization (FISH) and multiple molecular methods. The molecular methods included analysis of microbial diversity by 1) direct 16S and D2LSU rRNA gene Microseq 2) construction of near full-length 16S rRNA gene clone libraries with subsequent Sanger sequencing for most samples, 3) the Ibis T5000 biosensor and 4) 454-based pyrosequencing. Furthermore, quantitative PCR (qPCR) was used to verify and determine the relative abundance of Streptococcus pyogenes in samples.

Results

For 70 % of the surgical samples it was possible to identify microorganisms by culture. Some samples did not result in growth (presumably due to administration of antimicrobial therapy prior to sampling). The molecular methods identified microorganisms in 90 % of the samples, and frequently detected additional microorganisms when compared to culture. Although the molecular methods generally gave concordant results, our results indicate that Microseq may misidentify or overlook microorganisms that can be detected by other molecular methods.

Half of the patients were found to be infected with S. pyogenes, but several atypical findings were also made including infection by a) Acinetobacter baumannii, b) Streptococcus pneumoniae, and c) fungi, mycoplasma and Fusobacterium necrophorum.

Conclusion

The study emphasizes that many pathogens can be involved in NSTIs, and that no specific “NSTI causing” combination of species exists. This means that clinicians should be prepared to diagnose and treat any combination of microbial pathogens. Some of the tested molecular methods offer a faster turnaround time combined with a high specificity, which makes supplemental use of such methods attractive for identification of microorganisms, especially for fulminant life-threatening infections such as NSTI.

Polymerase Chain Reaction-Electrospray-Time-of-Flight Mass Spectrometry Versus Culture for Bacterial Detection in Septic Arthritis and Osteoarthritis

Background: Preliminary studies have identified known bacterial pathogens in the knees of patients with osteoarthritis (OA) before arthroplasty. Aims: The current study was designed to determine the incidence and types of bacteria present in the synovial fluid of native knee joints from adult patients with diagnoses of septic arthritis and OA. Patients and Methods: Patients were enrolled between October 2010 and January 2013. Synovial fluid samples from the affected knee were collected and evaluated with both traditional microbial culture and polymerase chain reaction–electrospray ionization–time-of-flight mass spectrometry (molecular diagnostics [MDx]) to prospectively characterize the microbial content. Patients were grouped by diagnosis into one of two cohorts, those with clinical suspicion of septic arthritis (n = 44) and those undergoing primary arthroplasty of the knee for OA (n = 21). In all cases where discrepant culture and MDx results were obtained, we performed species-specific 16S rRNA fluorescence in situ hybridization (FISH) as a confirmatory test. Results: MDx testing identified bacteria in 50% of the suspected septic arthritis cases and 29% of the arthroplasty cases, whereas culture detected bacteria in only 16% of the former and 0% of the latter group. The overall difference in detection rates for culture and MDx was very highly significant, p-value = 2.384 × 10⁻⁷. All of the culture-positive cases were typed as Staphylococcus aureus. Two of the septic arthritis cases were polymicrobial as was one of the OA cases by MDx. FISH testing of the specimens with discordant results supported the MDx findings in 91% (19/21) of the cases, including one case where culture detected S. aureus and MDx detected Streptococcus agalactiae.Conclusions: MDx were more sensitive than culture, as confirmed by FISH. FISH only identifies bacteria that are embedded or infiltrated within the tissue and is thus not susceptible to contamination. Not all suspected cases of septic arthritis contain bacteria, but a significant percent of patients with OA, and no signs of infection, have FISH-confirmed bacterial biofilms present in the knee.

Emperor's new clothes: Is particle disease really infected particle disease?

Aseptic loosening remains the most significant long-term complication of total hip replacement. The current paradigm points to an inflammatory response to wear particles as its main trigger. Recently, there have been increasing numbers of positive bacterial isolates reported among patients with clinically absent infection. This paper reviews existing evidence on possible involvement of bacteria and microbial-associated molecular patterns in the pathology of so-called "aseptic loosening." © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:1497-1504, 2016.

Direct demonstration of bacterial biofilms on prosthetic mesh after ventral herniorrhaphy

BACKGROUND

Prosthetic mesh is employed routinely in the treatment of ventral and parastomal hernias, but its use can lead to major complications, including infection, extrusion, and fistula. Bacterial biofilms have been posited to play a role in mesh-related infection, but although bacteria have been noted to form biofilms on mesh surfaces in vitro, they have never been visualized directly in biofilms on mesh recovered from patients experiencing infectious complications.

METHODS

Five patients who developed complications after ventral hernia repair with prosthetic mesh were operated on again. Explanted mesh was examined for biofilm with confocal laser scanning microscopy (CLSM) and fluorescence in situ hybridization (FISH). In two cases, a novel molecular assay (the Ibis T5000) was used to characterize the biofilm-forming bacteria.

RESULTS

The CLSM examination demonstrated adherent biofilms on mesh surfaces in all five patients. Biofilms also were noted on investing fibrous tissue. The FISH study was able to discriminate between bacterial species in polymicrobial biofilms. In two patients the Ibis T5000 detected more species of constituent biofilm bacteria than did standard culture. Removal of the mesh and reconstruction with autologous tissues or biologic materials resolved the presenting complaints in all cases.

CONCLUSION

Bacterial biofilms should be considered an important contributor to the pathology and complications associated with prosthetic mesh implanted in the abdominal wall. If biofilms are present, complete removal of the mesh and repair of the resulting defect without alloplastic materials is an effective intervention.

Presence of bacteria in failed anterior cruciate ligament reconstructions

BACKGROUND

Novel microbial detection technologies have revealed that chronic bacterial biofilms, which are recalcitrant to antibiotic treatment, are common in failed orthopedic procedures.

QUESTIONS

Are bacteria present on failed anterior cruciate ligament (ACL) reconstructions? Is there a difference in the presence or nature of bacteria in failed ACL reconstructions relative to a control set of healthy ACL's?

METHODS

We used a case-control study design, where we analyzed the bacterial composition of 10 failed ACL reconstructions and compared it to 10 native ACL's harvested during total knee arthroplasty. The IBIS Universal Biosensor was used to determine the nature of bacteria on ACL specimens, and fluorescent in situ hybridization (FISH) was used to visualize bacteria in a subset of cases.

RESULTS

Bacteria are present in failed ACL reconstructions. Bacteria are present in ACL's harvested during total knee arthroplasty, but the nature of the species differs significantly between experimental and control sets. Twelve genera were detected in the experimental set (in both allografts and autografts), and in four samples multiple species were detected. In contrast, the control group was characterized by presence of Propionibacterium acnes.

CONCLUSIONS

We demonstrate the presence of bacteria on failed ACLs surgeries, and open the door to investigate whether and how bacteria and the associated immune responses could possibly contribute to graft failure.

CLINICAL RELEVANCE

If microbial pathogens can be linked to failed grafts, it could provide: (1) markers for early diagnosis of abnormal healing in ACL surgeries, and (2) targets for early treatment to prevent additional reconstruction surgeries.

Towards diagnostic guidelines for biofilm-associated infections

Biofilms associated with the human body, particularly in typically sterile locations, are difficult to diagnose and treat effectively because of their recalcitrance to conventional antibiotic therapy and host immune responses. The study of biofilms in medicine today requires a translational approach, with examination of clinically relevant biofilms in the context of specific anatomic sites, host tissues, and diseases, focusing on what can be done to mitigate their pathologic consequences. This review, which grew out of a discussion session on clinical biofilms at the 5th ASM Biofilm Conference in Cancun, Mexico, is designed to give an overview of biofilm-associated infections (BAI) and to propose a platform for further discussion that includes clinicians, medical microbiologists, and biofilm researchers who are stakeholders in advancing the scientific pursuit of better diagnosis and treatment of BAI to mitigate their human and healthcare costs. It also highlights the need for better diagnostic markers, which exploit the difference between planktonic and biofilm cells.

Characterization of bacterial communities in venous insufficiency wounds by use of conventional culture and molecular diagnostic methods

Microbial infections delay wound healing, but the effect of the composition of the wound microbiome on healing parameters is unknown. To better understand bacterial communities in chronic wounds, we analyzed debridement samples from lower-extremity venous insufficiency ulcers using the following: conventional anaerobic and aerobic bacterial cultures; the Ibis T5000 universal biosensor (Abbott Molecular); and 16S 454 FLX titanium series pyrosequencing (Roche). Wound debridement samples were obtained from 10 patients monitored clinically for at least 6 months, at which point 5 of the 10 sampled wounds had healed. Pyrosequencing data revealed significantly higher bacterial abundance and diversity in wounds that had not healed at 6 months. Additionally, Actinomycetales was increased in wounds that had not healed, and Pseudomonadaceae was increased in wounds that had healed by the 6-month follow-up. Baseline wound surface area, duration, or analysis by Ibis or conventional culture did not reveal significant differences between wounds that healed after 6 months and those that did not. Thus, pyrosequencing identified distinctive baseline characteristics of wounds that did not heal by the 6-month follow-up, furthering our understanding of potentially unique microbiome characteristics of chronic wounds.