What is slough? Defining the proteomic and microbial composition of slough and its implications for wound healing

Slough is a well-known feature of non-healing wounds. This pilot study aims to determine the proteomic and microbiologic components of slough as well as interrogate the associations between wound slough components and wound healing. Ten subjects with slow-to-heal wounds and visible slough were enrolled. Aetiologies included venous stasis ulcers, post-surgical site infections and pressure ulcers. Patient co-morbidities and wound healing outcome at 3-months post-sample collection was recorded. Debrided slough was analysed microscopically, through untargeted proteomics, and high-throughput bacterial 16S-ribosomal gene sequencing. Microscopic imaging revealed wound slough to be amorphous in structure and highly variable. 16S-profiling found slough microbial communities to associate with wound aetiology and location on the body. Across all subjects, slough largely consisted of proteins involved in skin structure and formation, blood-clot formation and immune processes. To predict variables associated with wound healing, protein, microbial and clinical datasets were integrated into a supervised discriminant analysis. This analysis revealed that healing wounds were enriched for proteins involved in skin barrier development and negative regulation of immune responses. While wounds that deteriorated over time started off with a higher baseline Bates-Jensen Wound Assessment Score and were enriched for anaerobic bacterial taxa and chronic inflammatory proteins. To our knowledge, this is the first study to integrate clinical, microbiome, and proteomic data to systematically characterise wound slough and integrate it into a single assessment to predict wound healing outcome. Collectively, our findings underscore how slough components can help identify wounds at risk of continued impaired healing and serves as an underutilised biomarker.

RNA-sequencing of paired tape-strips and skin biopsies in atopic dermatitis reveals key differences

BACKGROUND

Skin tape-strips and biopsies are widely used methods for investigating the skin in atopic dermatitis (AD). Biopsies are more commonly used but can cause scarring and pain, whereas tape-strips are noninvasive but sample less tissue. The study evaluated the performance of skin tape-strips and biopsies for studying AD.

METHODS

Whole-transcriptome RNA-sequencing was performed on paired tape-strips and biopsies collected from lesional and non-lesional skin from AD patients (n = 7) and non-AD controls (n = 5). RNA yield, mapping efficiency, and differentially expressed genes (DEGs) for the two methods (tape-strip/biopsy) and presence of AD (AD/non-AD) were compared.

RESULTS

Tape-strips demonstrated a lower RNA yield (22 vs. 4596 ng) and mapping efficiency to known genes (28% vs. 93%) than biopsies. Gene-expression profiles of paired tape-strips and biopsies demonstrated a medium correlation (R2  = 0.431). Tape-strips and biopsies demonstrated systematic differences in measured expression levels of 6483 genes across both AD and non-AD samples. Tape-strips preferentially detected many itch (CCL3/CCL4/OSM) and immune-response (CXCL8/IL4/IL5/IL22) genes as well as markers of epidermal dendritic cells (CD1a/CD207), while certain cytokines (IL18/IL37), skin-barrier genes (KRT2/FLG2), and dermal fibroblasts markers (COL1A/COL3A) were preferentially detected by biopsies. Tape-strips identified more DEGs between AD and non-AD (3157 DEGs) then biopsies (44 DEGs). Tape-strips also detected higher levels of bacterial mRNA than biopsies.

CONCLUSIONS

This study concludes that tape-strips and biopsies each demonstrate respective advantages for measuring gene-expression changes in AD. Thus, the specific skin layers and genes of interest should be considered before selecting either method.

Novel sampling technique maintaining the two-dimensional organization of microbes during cultivation from chronic wounds: The Imprint method

This study aimed to develop and validate "the Imprint method,", a technique for sampling microbes from chronic wounds while preserving their two-dimensional spatial organization. We used nylon filters to sample bacteria and compared with sampling using Eswabs in 12 patients. The Imprint method identified a mean of 0.93 unique species more than Eswab (4.3 ± 2.2 and 3.4 ± 1.4 unique species, respectively; mean ± SD; n = 30). Accuracy between the Eswab and the Imprint method was 93.2% and in cases of disagreement between methods, Imprint had a higher sensitivity in 6/8 of the most prevalent species. In vitro validation confirmed that the Imprint method could transfer bacterial colonies while replicating their two-dimensional organization and the area covered by bacteria on the plate sampled. Clinical testing demonstrated that the imprint method is a rapid and feasible technique that identified more unique bacterial species than Eswab with a good agreement between methods but that Imprint was better at detecting important pathogens such as Staphylococcus aureus and Pseudomonas aeruginosa. The Imprint method is a novel technique that cultures and records the two-dimensional organization of microbes, providing an alternative or supplement to conventional surface culture using Eswab.

Inhibition of Pseudomonas aeruginosa quorum sensing by chemical induction of the MexEF-oprN efflux pump

The cell-to-cell communication system quorum sensing (QS), used by various pathogenic bacteria to synchronize gene expression and increase host invasion potentials, is studied as a potential target for persistent infection control. To search for novel molecules targeting the QS system in the Gram-negative opportunistic pathogen Pseudomonas aeruginosa, a chemical library consisting of 3,280 small compounds from LifeArc was screened. A series of 10 conjugated phenones that have not previously been reported to target bacteria were identified as inhibitors of QS in P. aeruginosa. Two lead compounds (ethylthio enynone and propylthio enynone) were re-synthesized for verification of activity and further elucidation of the mode of action. The isomeric pure Z-ethylthio enynone was used for RNA sequencing, revealing a strong inhibitor of QS-regulated genes, and the QS-regulated virulence factors rhamnolipid and pyocyanin were significantly decreased by treatment with the compounds. A transposon mutagenesis screen performed in a newly constructed lasB-gfp monitor strain identified the target of Z-ethylthio enynone in P. aeruginosa to be the MexEF-OprN efflux pump, which was further established using defined mex knockout mutants. Our data indicate that the QS inhibitory capabilities of Z-ethylthio enynone were caused by the drainage of intracellular signal molecules as a response to chemical-induced stimulation of the MexEF-oprN efflux pump, thereby inhibiting the autogenerated positive feedback and its enhanced signal-molecule synthesis.

Bacterial aerobic respiration is a major consumer of oxygen in sputum from patients with acute lower respiratory tract infection

Bacterial aerobic respiration may determine the outcome of antibiotic treatment in experimental settings, but the clinical relevance of bacterial aerobic respiration for the outcome of antibiotic treatment has not been tested. Therefore, we hypothesized that bacterial aerobic respiration is higher in sputum from patients with acute lower respiratory tract infections (aLRTI), than in sputum from patients with chronic LRTI (cLRTI), where the bacteria persist despite antibiotic treatment. The bacterial aerobic respiration was determined according to the dynamics of the oxygen (O2 ) concentration in sputum from aLRTI patients (n = 52). This result was evaluated by comparison to previously published data from patients with cLRTI. O2 consumption resulting in anoxic zones was more frequent in sputum with detected bacterial pathogens. The bacterial aerobic respiration in aLRTI sputum approximated 55% of the total O2 consumption, which was significantly higher than previously published for cLRTI. The bacterial aerobic respiration in sputum was higher in aLRTI patients than previously seen in cLRTI patients, indicating the presence of bacteria with a sensitive physiology in aLRTI. These variations in bacterial physiology between aLRTI patients and cLRTI patients may contribute the huge difference in treatment success between the two patient groups.

Biofilms and core pathogens shape the tumor microenvironment and immune phenotype in colorectal cancer

Extensive research has explored the role of gut microbiota in colorectal cancer (CRC). Nonetheless, metatranscriptomic studies investigating the in situ functional implications of host-microbe interactions in CRC are scarce. Therefore, we characterized the influence of CRC core pathogens and biofilms on the tumor microenvironment (TME) in 40 CRC, paired normal, and healthy tissue biopsies using fluorescence in situ hybridization (FISH) and dual-RNA sequencing. FISH revealed that Fusobacterium spp. was associated with increased bacterial biomass and inflammatory response in CRC samples. Dual-RNA sequencing demonstrated increased expression of pro-inflammatory cytokines, defensins, matrix-metalloproteases, and immunomodulatory factors in CRC samples with high bacterial activity. In addition, bacterial activity correlated with the infiltration of several immune cell subtypes, including M2 macrophages and regulatory T-cells in CRC samples. Specifically, Bacteroides fragilis and Fusobacterium nucleatum correlated with the infiltration of neutrophils and CD4+ T-cells, respectively. The collective bacterial activity/biomass appeared to exert a more significant influence on the TME than core pathogens, underscoring the intricate interplay between gut microbiota and CRC. These results emphasize how biofilms and core pathogens shape the immune phenotype and TME in CRC while highlighting the need to extend the bacterial scope beyond CRC pathogens to advance our understanding and identify treatment targets.

Characterization of patients with odontogenic necrotizing soft tissue infections in the head and neck area. A retrospective analysis

OBJECTIVE

Necrotizing soft-tissue infection (NSTI) in the head and neck area may develop from odontogenic infections. The aim of this study was to characterize patients with NSTI in the head and neck with odontogenic origin in a well-defined prospectively collected cohort.

MATERIAL AND METHODS

Patients with NSTI in the head and neck, hospitalized between 2013 and 2017 at Copenhagen University Hospital and registered in the Scandinavian INFECT database were included. Medical records of identified patients and from the INFECT database were screened for a defined set of data including the primary focus of infection, comorbidities, predisposing factors, clinical and radiographic diagnostics, course of treatment, and treatment outcome.

RESULTS

Thirty-five patients with NSTI in the head and neck area were included in the study. A total of 54% had odontogenic origin, primarily from mandibular molars, and 94% had radiographic signs of infectious oral conditions. Overall, comorbidities were reported in 51% with cardiovascular disease being the most prevalent. In 20%, no comorbidities or predisposing conditions could be identified. The overall 30-day mortality rate was 9%.

CONCLUSIONS

More than half of NSTI cases in the head and neck region had an odontogenic origin, and special attention should be paid to infections related to mandibular molars.

Pharmacokinetics of Locally Applied Antibiotic Prophylaxis for Implant-Based Breast Reconstruction

Importance

Antibiotic irrigation of breast implants is widely used internationally, but no clinical study has investigated the pharmacokinetics of antibiotic prophylaxis in the breast implant pocket.

Objectives

To evaluate how long locally applied gentamicin, cefazolin, and vancomycin concentrations in the implant pocket remain above the minimum inhibitory concentration (MIC) for the most common bacterial infections and to measure systemic uptake.

Design, Setting, and Participants

This prospective cohort study was performed at the Department of Plastic Surgery and Burns Treatment, Rigshospitalet, Copenhagen, Denmark, between October 25, 2021, and September 22, 2022, among 40 patients undergoing implant-based breast reconstruction who were part of the ongoing BREAST-AB trial (Prophylactic Treatment of Breast Implants With a Solution of Gentamicin, Vancomycin and Cefazolin Antibiotics for Women Undergoing Breast Reconstructive Surgery: a Randomized Controlled Trial). Patients were randomized to receive locally applied gentamicin, cefazolin, and vancomycin or placebo. Samples were obtained from the surgical breast drain and blood up to 10 days postoperatively.

Exposures

The breast implant and the implant pocket were irrigated with 160 μg/mL of gentamicin, 2000 μg/mL of cefazolin, and 2000 μg/mL of vancomycin in a 200-mL saline solution.

Main Outcomes and Measures

The primary outcome was the duration of antibiotic concentrations above the MIC breakpoint for Staphylococcus aureus according to the Clinical and Laboratory Standards Institute: gentamicin, 4 μg/mL; cefazolin, 2 μg/mL; and vancomycin, 2 μg/mL. Secondary outcomes included the time above the MIC for Pseudomonas aeruginosa and other relevant bacteria, as well as systemic uptake.

Results

The study included 40 patients (median age, 44.6 years [IQR, 38.3-51.4 years]; median body mass index, 23.9 [IQR, 21.7-25.9]) with a median number of 3 drain samples (range, 1-10 drain samples) and 2 blood samples (range, 0-6 blood samples). Vancomycin and cefazolin remained above the MIC for S aureus significantly longer than gentamicin (gentamicin, 0.9 days [95% CI, 0.5-1.2 days] for blood samples vs 6.9 days [95% CI, 2.9 to 10.9 days] for vancomycin [P = .02] vs 3.7 days [95% CI, 2.2-5.2 days] for cefazolin [P = .002]). The gentamicin level remained above the MIC for P aeruginosa for 1.3 days (95% CI, 1.0-1.5 days). Only cefazolin was detectable in blood samples, albeit in very low concentrations (median concentration, 0.04 μg/mL [range, 0.007-0.1 μg/mL]).

Conclusions and Relevance

This study suggests that patients treated with triple-antibiotic implant irrigation during breast reconstruction receive adequate prophylaxis for S aureus and other common implant-associated, gram-positive bacteria. However, the protection against P aeruginosa may be inadequate.

Microbial Primer: In vivo biofilm

In this primer on biofilms and their role in infections, we trace the historical roots of microbial understanding from Van Leeuwenhoek's observations to Bill Costerton's groundbreaking work, which solidified biofilms' significance in infections. In vivo biofilm research, investigating patient samples and utilizing diverse host models, has yielded invaluable insights into these complex microbial communities. However, it comes with several challenges, particularly regarding replicating biofilm infections accurately in the laboratory. In vivo biofilm analyses involve various techniques, revealing biofilm architecture, composition, and behaviour, while gaps in knowledge persist regarding infection initiation and source, diversity, and the Infectious Microenvironment (IME). Ultimately, the study of biofilms in infections remains a dynamic and evolving field poised to transform our approach to combat biofilm-associated diseases.

Biofilm formation on endovascular aneurysm repair (EVAR) grafts-a proof of concept in vitro model

OBJECTIVES

An endovascular aneurysm repair (EVAR) graft is a catheter-implanted vascular prosthesis and is the preferred treatment for patients with aortic aneurysm. If an EVAR graft becomes the focus of infection, the treatment possibilities are limited because it is technically difficult to remove the graft to obtain source control. This study examines whether Pseudomonas aeruginosa and Staphylococcus aureus form biofilm on EVAR prostheses.

METHODS

EVAR graft sections were exposed to bacteria at 102 or 108 colony forming units (CFU)/mL in lysogeny broth and Krebs-Ringer at 37°C, bacterial biofilm formation was evaluated by scanning electron microscopy and counting CFU on the graft sections after antibiotic exposure at × 10 minimal inhibitory concentration. Bacteria were tested for tolerance to benzylpenicillin, tobramycin, and ciprofloxacin.

RESULTS

Bacterial exposure for 15 minutes established biofilms on all prosthesis fragments (6/6 replicates). After 4 hours, bacteria were firmly attached to the EVAR prostheses and resisted washing. After 18-24 hours, the median CFU/g of EVAR graft reached 5.2 × 108 (1.15 × 108-1.1 × 109) for S. aureus and 9.1 × 107 (3.5 × 107-6.25 × 108) for P. aeruginosa. Scanning electron microscopy showed bacterial attachment to the graft pieces. There was a time-dependent development of tolerance with approximately 20 (tobramycin), 560 (benzylpenicillin), and 600 (ciprofloxacin) times more S. aureus surviving antibiotic exposure in 24- compared with 0-hour-old biofilm. Five (tobramycin) and 170 times (ciprofloxacin) more P. aeruginosa survived antibiotic exposure in 24- compared with 0-hour-old biofilms.

DISCUSSION

Our results show that bacteria can rapidly adhere to and subsequently form antibiotic-tolerant biofilms on EVAR graft material in concentrations equivalent to levels seen in transient bacteraemia in vivo. Potentially, the system can be used for identifying optimal treatment combinations for infected EVAR prosthesis.

Reduced Skin Microbiome Diversity in Infancy Is Associated with Increased Risk of Atopic Dermatitis in High-Risk Children

It is currently unknown whether alterations in the skin microbiome exist before development of atopic dermatitis (AD). In this prospective Danish birth cohort of 300 children, we examined whether skin microbiome alterations during the first 2 months of life were associated with an increased risk of AD in the first 2 years and its severity after adjustment for environmental factors and selected skin chemokine and natural moisturizing factor levels. We found no overall association between the skin microbiome at birth and age 2 months and AD during the first 2 years of life. However, when restricting the analysis to children with at least one parent with atopy, a lower alpha diversity at age 2 months was associated with an increased risk of AD (adjusted hazard ratio = 1.7, 95% confidence interval = 1.1-2.6). We observed a stronger association in children where both parents had atopy (adjusted hazard ratio = 4.4, 95% confidence interval = 1.1-18.2). The putative pathogenic role of changes in the skin microbiome on AD risk remains uncertain but may play a role in those with an atopic predisposition.

A simplified bacterial community found within the epidermis than at the epidermal surface of atopic dermatitis patients and healthy controls

There has been considerable research into the understanding of the healthy skin microbiome. Similarly, there is also a considerable body of research into whether specific microbes contribute to skin disorders, with atopic dermatitis (AD) routinely linked to increased Staphylococcus aureus (S. aureus) colonisation. In this study, the epidermal surface of participants was sampled using swabs, while serial tape-stripping (35 tapes) was performed to sample through the stratum corneum. Samples were taken from AD patients and healthy controls, and the bacterial communities were profiled by metabarcoding the universal V3-V4 16S rRNA region. Results show that the majority of bacterial richness is located within the outermost layers of the stratum corneum, however there were many taxa that were found almost exclusively at the very outermost layer of the epidermis. We therefore hypothesise that tape-stripping can be performed to investigate the 'core microbiome' of participants by removing environmental contaminants. Interestingly, significant community variation between AD patients and healthy controls was only observable at the epidermal surface, yet a number of individual taxa were found to consistently differ with AD status across the entire epidermis (i.e. both the epidermal surface and within the epidermis). Sampling strategy could therefore be tailored dependent on the hypothesis, with sampling for forensic applications best performed using surface swabs and outer tapes, while profiling sub-surface communities may better reflect host genome and immunological status.

Direct 16S/18S rRNA Gene PCR Followed by Sanger Sequencing as a Clinical Diagnostic Tool for Detection of Bacterial and Fungal Infections: a Systematic Review and Meta-Analysis

rRNA gene Sanger sequencing is being used for the identification of cultured pathogens. A new diagnostic approach is sequencing of uncultured samples by using the commercial DNA extraction and sequencing platform SepsiTest (ST). The goal was to analyze the clinical performance of ST with a focus on nongrowing pathogens and the impact on antibiotic therapy. A literature search used PubMed/Medline, Cochrane, Science Direct, and Google Scholar. Eligibility followed PRISMA-P criteria. Quality and risk of bias were assessed drawing on QUADAS-2 (quality assessment of diagnostic accuracy studies, revised) criteria. Meta-analyses were performed regarding accuracy metrics compared to standard references and the added value of ST in terms of extra found pathogens. We identified 25 studies on sepsis, infectious endocarditis, bacterial meningitis, joint infections, pyomyositis, and various diseases from routine diagnosis. Patients with suspected infections of purportedly sterile body sites originated from various hospital wards. The overall sensitivity (79%; 95% confidence interval [CI], 73 to 84%) and specificity (83%; 95% CI, 72 to 90%) were accompanied by large effect sizes. ST-related positivity was 32% (95% CI, 30 to 34%), which was significantly higher than the culture positivity (20%; 95% CI, 18 to 22%). The overall added value of ST was 14% (95% CI, 10 to 20%) for all samples. With 130 relevant taxa, ST uncovered high microbial richness. Four studies demonstrated changes of antibiotic treatment at 12% (95% CI, 9 to 15%) of all patients upon availability of ST results. ST appears to be an approach for the diagnosis of nongrowing pathogens. The potential clinical role of this agnostic molecular diagnostic tool is discussed regarding changes of antibiotic treatment in cases where culture stays negative.

Single cells and bacterial biofilm populations in chronic wound infections

Chronic wounds and chronic ulcers are an increasing problem associated with high health care burden and patient burden. The arrested healing of chronic wounds has, in part, been attributed to the presence of biofilms. Substantial research has documented the presence of biofilms in chronic wounds, and many mechanisms of host-pathogen interactions have been uncovered to explain the arrested healing. However, the paradigm of whether biofilms are only observed in chronic infections was recently challenged when biofilms were also observed in acute infections. Here, we characterize the distribution of bacteria in lower leg wounds with particular emphasis on Pseudomonas aeruginosa and Staphylococcus aureus by confocal laser scanning microscopy combined with PNA-FISH staining and routine culture of bacteria. We show that 40% of wounds contained either P. aeruginosa or S. aureus biofilms and demonstrate the presence of scattered single cells in tissues stained with a universal bacterial PNA-FISH probe. Thus, we demonstrate that chronic wounds do not only harbor bacteria organized in biofilms, but also carry populations of scattered single cells and small cell clusters of only a few bacteria. Our findings may influence diagnostic tools being developed to only target biofilms, where single-cell subpopulations thus may be overlooked and possibly lead to false-negative results.

What's in a name? Characteristics of clinical biofilms

In vitro biofilms are communities of microbes with unique features compared to individual cells. Biofilms are commonly characterized by physical traits like size, adhesion, and a matrix made of extracellular substances. They display distinct phenotypic features, such as metabolic activity and antibiotic tolerance. However, the relative importance of these traits depends on the environment and bacterial species. Various mechanisms enable biofilm-associated bacteria to withstand antibiotics, including physical barriers, physiological adaptations, and changes in gene expression. Gene expression profiles in biofilms differ from individual cells but, there is little consensus among studies and so far, a 'biofilm signature transcriptome' has not been recognized. Additionally, the spatial and temporal variability within biofilms varies greatly depending on the system or environment. Despite all these variable conditions, which produce very diverse structures, they are all noted as biofilms. We discuss that clinical biofilms may differ from those grown in laboratories and found in the environment and discuss whether the characteristics that are commonly used to define and characterize biofilms have been shown in infectious biofilms. We emphasize that there is a need for a comprehensive understanding of the specific traits that are used to define bacteria in infections as clinical biofilms.

Endolysin Inhibits Skin Colonization by Patient-Derived Staphylococcus Aureus and Malignant T-Cell Activation in Cutaneous T-Cell Lymphoma

Staphylococcus aureus is suspected to fuel disease activity in cutaneous T-cell lymphomas. In this study, we investigate the effect of a recombinant, antibacterial protein, endolysin (XZ.700), on S. aureus skin colonization and malignant T-cell activation. We show that endolysin strongly inhibits the proliferation of S. aureus isolated from cutaneous T-cell lymphoma skin and significantly decreases S. aureus bacterial cell counts in a dose-dependent manner. Likewise, ex vivo colonization of both healthy and lesional skin by S. aureus is profoundly inhibited by endolysin. Moreover, endolysin inhibits the patient-derived S. aureus induction of IFNγ and the IFNγ-inducible chemokine CXCL10 in healthy skin. Whereas patient-derived S. aureus stimulates activation and proliferation of malignant T cells in vitro through an indirect mechanism involving nonmalignant T cells, endolysin strongly inhibits the effects of S. aureus on activation (reduced CD25 and signal transducer and activator of transcription 5 phosphorylation) and proliferation (reduced Ki-67) of malignant T cells and cell lines in the presence of nonmalignant T cells. Taken together, we provide evidence that endolysin XZ.700 inhibits skin colonization, chemokine expression, and proliferation of pathogenic S. aureus and blocks their potential tumor-promoting effects on malignant T cells.

A collagen-based layered chronic wound biofilm model for testing antimicrobial wound products

A new in vitro chronic wound biofilm model was recently published, which provided a layered scaffold simulating mammalian tissue composition on which topical wound care products could be tested. In this paper, we updated the model even further to mimic the dynamic influx of nutrients from below as is the case in a chronic wound. The modified in vitro model was created using collagen instead of agar as the main matrix component and contained both Staphylococcus aureus and Pseudomonas aeruginosa. The model was cast in transwell inserts and then placed in wound simulating media, which allowed for an exchange of nutrients and waste products across a filter. Three potential wound care products and chlorhexidine digluconate 2% solution as a positive control were used to evaluate the model. The tested products were composed of hydrogels made from completely biodegradable starch microspheres carrying different active compounds. The compounds were applied topically and left for 2-4 days. Profiles of oxygen concentration and pH were measured to assess the effect of treatments on bacterial activity. Confocal microscope images were obtained of the models to visualise the existence of microcolonies. Results showed that the modified in vitro model maintained a stable number of the two bacterial species over 6 days. In untreated models, steep oxygen gradients developed and pH increased to >8.0. Hydrogels containing active compounds alleviated the high oxygen consumption and decreased pH drastically. Moreover, all three hydrogels reduced the colony forming units significantly and to a larger extent than the chlorhexidine control treatment. Overall, the modified model expressed several characteristics similar to in vivo chronic wounds.

Antibiotic implant irrigation and deep infection: A retrospective study of 1508 patients undergoing breast reconstruction with implants

BACKGROUND

Antibiotic implant irrigation is increasingly used to prevent deep infection after implant-based breast reconstruction. However, there is limited evidence of the clinical effect. In this study, we compare the risk of a deep infection in a Danish population of women who either received antibiotic implant irrigation with gentamycin or vancomycin, or no irrigation.

METHODS

We retrospectively reviewed consecutive patients undergoing all types of breast reconstruction with implants at Rigshospitalet and Herlev Hospital, Denmark, in 2010-2019. Logistic regression was used to compare the risk of deep infection between no irrigation and irrigation with gentamicin or vancomycin, and to account for the difference in risk between patient subgroups and risk factors.

RESULTS

We included 1508 patients who received antibiotic irrigation with gentamicin (500 patients), vancomycin (304 patients) or no irrigation (704 patients). The univariable risk analysis showed a significant decreased risk of deep infection using gentamicin irrigation compared with no irrigation (OR 0.58, p<0.05). However, when adjusting for risk factors for infection, there was no significant decrease in the risk of infection when using gentamicin (OR 0.90, p=0.71) or vancomycin (OR 1.0, p=0.99) compared with the control group.

CONCLUSIONS

We found no significant effect of using antibiotic implant irrigation after isolating it from risk factors for deep infection. However, due to the limitations of the study, we cannot conclude that there is no effect of antibiotic implant irrigation. There is a need for a randomized, placebo-controlled trial to investigate the effect, and potential side-effects, of antibiotic implant irrigation.

E-cadherin and aquaporin-3 are downregulated in wound edges of human chronic wounds

Chronic wounds are defined as wounds that fail to proceed through the normal phases of wound healing; a complex process involving different dynamic events including migration of keratinocytes in the epidermis. Chronic wounds are estimated to affect 1-2% of the human population worldwide and are a major socioeconomic burden. The prevalence of chronic wounds is expected to increase with the rising number of elderly and patients with diabetes and obesity, who are at high risk of developing chronic wounds. Since E-cadherin and the water channel aquaporin-3 are important for both skin function and cell migration, and aquaporin-3 is furthermore involved in wound healing of the skin demonstrated by impaired wound healing in aquaporin-3-null mice, we hypothesized that E-cadherin and aquaporin-3 expression may be dysregulated in chronic wounds. Therefore, we investigated the expression of E-cadherin and aquaporin-3 in biopsies from the edges of chronic wounds from human patients. This was accomplished by immunohistochemical stainings of E-cadherin and aquaporin-3 on serial sections followed by qualitative evaluation of staining patterns, which revealed low expression of both E-cadherin and aquaporin-3 at the wound edge. Future studies are needed to reveal if this downregulation is associated with the pathophysiology of chronic wounds.

Protocol to assess metabolic activity of Pseudomonas aeruginosa by measuring heat flow using isothermal calorimetry

Here, we present a protocol for assessing metabolic activity of bacterial populations by measuring heat flow using isothermal calorimetry. We outline the steps for preparing the different growth models of Pseudomonas aeruginosa and performing continuous metabolic activity measurements in the calScreener. We detail simple principal component analysis to differentiate between metabolic states of different populations and probabilistic logistic classification to assess resemblance to wild-type bacteria. This protocol for fine-scale metabolic measurement can aid in understanding microbial physiology. For complete details on the use and execution of this protocol, please refer to Lichtenberg et al. (2022).¹.

Cerebral abscesses with odontogenic origin: a population-based cohort study

Objectives

Recent studies have indicated that cerebral abscess (CA) patients with odontogenic origin are on the rise. However, CA patients are often poorly characterized and with an unknown etiologic background. The purpose of this study is to identify and characterize CA patients that may have an odontogenic origin based on microbiologic, radiographic, and/or clinical findings.

Materials and methods

This is a population-based cohort study analyzing retrospective and prospective data from CA patients. Radiographic examinations of panoramic radiographs (PRs) or computed tomography (CT) scans were conducted. CA patients characterized with odontogenic origin required the fulfilment of the following criteria on admission: (1) Oral pathologic conditions were the only bacterial infections present, (2) oral microorganisms were isolated in the purulent exudate from the brain, and (3) radiographically and/or clinical recordings of oral pathologic conditions.

Results

A total of 44 patients could be included in this study of which 25 (57%) were characterized as having CA with a likely odontogenic origin. Type two diabetes (T2D) (p = 0.014) and microorganisms of the Streptococcus anginosus group (SAG) (p < 0.01) were overrepresented in patients with CAs of odontogenic origin.

Conclusions

Odontogenic infections may cause CAs to a greater extent than previously assumed. T2D was overrepresented among patients with odontogenic CA. When microorganisms of the SAG were isolated from the brain pus, CA patients had a predisposing odontogenic or sinus infection.

Clinical relevance

The identification of patients with a likely odontogenic CA will contribute to understanding the etiology of the infectious disease and highlighting the importance of preserving oral health.

Defining the temporal relationship between the skin microbiome, immune response and skin barrier function during flare and resolution of atopic dermatitis: protocol of a Danish intervention study

INTRODUCTION

Lesional skin of atopic dermatitis (AD) is often colonised by Staphylococcus aureus and the bacterial abundance increases during a flare. However, the role of S. aureus and the skin microbiome in the pathogenesis of AD, including its influence on the dysfunctional skin barrier and immune response, remains to be elucidated. In this study, the temporal relationship between alterations in the skin barrier function, inflammation and microbiome is examined in adults with AD.

METHODS AND ANALYSIS

This clinical study consists of 81 adult patients with AD, as defined by the Hanifin and Rajka criteria, and 41 age and sex-matched controls. The objectives are to examine alterations in the skin microbiome, skin barrier and immune response during (1) an untreated AD flare, (2) an AD flare treated with topical corticosteroids (TCS), (3) an AD flare treated with systemic dicloxacillin/placebo and TCS or (4) cutaneous exposure to either autologous S. aureus, staphylococcal enterotoxin B or a vehicle. Skin biopsies, tape strips, skin and nasal swabs are collected and analysed using RNA sequencing, multiplex immunoassays, liquid chromatography-mass spectrometry and 16S rDNA. Blood samples are analysed for filaggrin gene mutations and leucocyte gene expression.

ETHICS AND DISSEMINATION

The scientific Ethical Committee of the Capital Region in Denmark (phases I and II: H-20011047, phases III and IV: H-21079287), the local data protection agency (phases I and II: P-2020-165, phases III and IV: P-2022-250) and the Danish Medicines Agency (phases III and IV: EudraCT 2021-006883-25, ClinicalTrials.gov: NCT05578482) have approved the studies. Participants will give written informed consent prior to study initiation. The study is conducted in accordance with the Helsinki Declaration. Outcomes will be presented at national and international conferences and in international peer-reviewed publications.

TRIAL REGISTRATION NUMBER

NCT05578482, EudraCT 2021-006883-2.

Adaptation of Pseudomonas aeruginosa biofilms to tobramycin and the quorum sensing inhibitor C-30 during experimental evolution requires multiple genotypic and phenotypic changes

In the present study we evaluated the fitness, antimicrobial susceptibility, metabolic activity, gene expression, in vitro production of virulence factors and in vivo virulence of experimentally evolved Pseudomonas aeruginosa PAO1. These strains were previously evolved in the presence of tobramycin and the quorum sensing inhibitor furanone C-30 (C-30) and carried mutations in mexT and fusA1. Compared to the wild-type (WT), the evolved strains show a different growth rate and different metabolic activity, suggesting they have an altered fitness. mexT mutants were less susceptible to C-30 than WT strains; they also show reduced susceptibility to chloramphenicol and ciprofloxacin, two substrates of the MexEF-OprN efflux pump. fusA1 mutants had a decreased susceptibility to aminoglycoside antibiotics, and an increased susceptibility to chloramphenicol. The decreased antimicrobial susceptibility and decreased susceptibility to C-30 was accompanied by a changed metabolic activity profile during treatment. The expression of mexE was significantly increased in mexT mutants and induced by C-30, suggesting that MexEF-OprN exports C-30 out of the bacterial cell. The in vitro production of virulence factors as well as virulence in two in vivo models of the strains evolved in the presence of C-30 was unchanged compared to the virulence of the WT. Finally, the evolved strains were less susceptible towards tobramycin (alone and combined with C-30) in an in vivo mouse model. In conclusion, this study shows that mutations acquired during experimental evolution of P. aeruginosa biofilms in the presence of tobramycin and C-30, are accompanied by an altered fitness, metabolism, mexE expression and in vitro and in vivo antimicrobial susceptibility.

Inoculum Concentration Influences Pseudomonas aeruginosa Phenotype and Biofilm Architecture

In infections, bacterial cells are often found as relatively small multicellular aggregates characterized by a heterogeneous distribution of phenotype, genotype, and growth rates depending on their surrounding microenvironment. Many laboratory models fail to mimic these characteristics, and experiments are often initiated from planktonic bacteria given optimal conditions for rapid growth without concerns about the microenvironmental characteristics during biofilm maturation. Therefore, we investigated how the initial bacterial concentration (henceforth termed the inoculum) influences the microenvironment during initial growth and how this affects the sizes and distribution of developed aggregates in an embedded biofilm model-the alginate bead biofilm model. Following 24 h of incubation, the viable biomass was independent of starting inoculum but with a radically different microenvironment which led to differences in metabolic activity depending on the inoculum. The inoculum also affected the number of cells surviving treatment with the antibiotic tobramycin, where the highest inoculum showed higher survival rates than the lowest inoculum. The change in antibiotic tolerance was correlated with cell-specific RNA content and O2 consumption rates, suggesting a direct role of metabolic activity. Thus, the starting number of bacteria results in different phenotypic trajectories governed by different microenvironmental characteristics, and we demonstrate some of the possible implications of such physiological gradients on the outcome of in vitro experiments. IMPORTANCE Biofilm aggregates grown in the alginate bead biofilm model bear resemblance to features of in vivo biofilms. Here, we show that changing the initial concentration of bacteria in the biofilm model leads to widely different behavior of the bacteria following an incubation period. This difference is influenced by the local conditions experienced by the bacteria during growth, which impact their response to antibiotic treatment. Our study provides a framework for manipulating aggregate sizes in in vitro biofilm models. It underlines the importance of how experiments are initiated, which can profoundly impact the outcomes and interpretation of microbiological experiments.

3D blood-brain barrier-organoids as a model for Lyme neuroborreliosis highlighting genospecies dependent organotropism

Lyme neuroborreliosis (LNB), a tick-borne infection caused by spirochetes within the Borrelia burgdorferi sensu lato (s.L.) complex, is among the most prevalent bacterial central nervous system (CNS) infections in Europe and the US. Here we have screened a panel of low-passage B. burgdorferi s.l. isolates using a novel, human-derived 3D blood-brain barrier (BBB)-organoid model. We show that human-derived BBB-organoids support the entry of Borrelia spirochetes, leading to swelling of the organoids and a loss of their structural integrity. The use of the BBB-organoid model highlights the organotropism between B. burgdorferi s.l. genospecies and their ability to cross the BBB contributing to CNS infection.

Prevalence of biofilms in acute infections challenges a longstanding paradigm

The significance of bacterial biofilm formation in chronic bacterial lung infections has long been recognized [1]. Likewise, chronic biofilm formation on medical devices is well accepted as a nidus for recurrent bacteremia [2,3]. Even though the prevailing paradigm relies on the dominance of planktonic bacteria in acute endobronchial infections, our understanding of the bacterial organization during acute infection is, so far, limited - virtually absent. However, by comparing similar clinical samples, we have recently demonstrated massive bacterial biofilm formation during acute lung infections resembling the immense bacterial biofilm formation during chronic lung infections. These findings pose major challenges to the basic paradigm of chronic infections being dominated by biofilm forming bacteria while acute infections are dominated by planktonic bacteria. As opposed to the similar high amount of bacterial biofilm found in chronic and acute lung infections, we found that the fast bacterial growth in acute lung infections differed from the slow bacterial growth in chronic lung infections. By highlighting these new findings, we review modes of improved treatment of biofilm infections and the relevance of bacterial growth rates for other bacterial biofilm infections than human lung infections.

Establishing a consensus on wound infection definitions

OBJECTIVES

The aim of this study was to establish an international, interorganisational consensus on wound infection terminology.

METHODS

This project consisted of definition scoping and a Delphi process to produce a consensus glossary for 18 wound infection terms. Recent guidelines/consensus documents were reviewed to identify 2-4 definitions for each term. An online consensus process was undertaken using the RAND Appropriateness Method, a consensus method for panels to reach agreement. International wound organisations nominated experts to participate, from whom 21 participants were selected to represent different organisations, geographic regions and disciplines. In the first consensus round, each term was presented alongside 2-3 definitions and participants nominated their preferred definition, with the majority vote used to select a baseline definition. The consensus process then proceeded, with participants using a 9-point Likert scale to score their level of agreement or disagreement with the definition for each term. Participants also provided a justification outlining the reason behind their rating. At the end of each round, an index was calculated to provide a quantitative evaluation indicating whether agreement or disagreement had been reached.

RESULTS

Reasoning statements were summarised and the definitions were adjusted to incorporate concepts identified by participants. The adjusted definition was presented in the next consensus round, together with the reasoning statements. Terms for which a final definition was not achieved in three consensus rounds were finalised with preferential voting using 2-3 definitions that had reached consensus.

PROJECT PROGRESS AND SIGNIFICANCE

The project generated a glossary of wound infection terms, endorsed through participation of 15 international organisations, for dissemination of guidelines and clinical decision-making/teaching tools.

IWII Wound Infection in Clinical Practice consensus document: 2022 update

ABSTRACT

Wound infection is a major challenge for clinicians globally, with accurate and timely identification of wound infection being critical to achieving clinical and cost-effective management, and promotion of healing. This paper presents an overview of the development of the International Wound Infection Institute (IWII)'s 2022 Wound Infection in Clinical Practice consensus document. The updated document summarises current evidence and provides multidisciplinary healthcare providers with effective guidance and support on terminology, paradigms related to biofilm, identification of wound infection, wound cleansing, debridement and antimicrobial stewardship. Integral to the update is revision of wound infection management strategies which are incorporated within the IWII's Wound Infection Continuum (IWII-WIC) and management plan. The aim of the 2022 IWII consensus document update was to provide an accessible and useful clinical resource in at least six languages, incorporating the latest evidence and current best practice for wound infection and prevention. Dissemination techniques for the consensus are discussed and highlighted.

Characterization of pig skin microbiome and appraisal as an in vivo subcutaneous injection model

Pig skin is commonly used in the medical industry as an injection model due to its compelling physiological affinity to human skin. However, the pig neck skin microflora remains largely uncharacterized, which may have undesirable implications for the translatability of results to humans. This study aimed to characterize pig neck skin microbiome with direct comparison with human skin microflora at emblematic injection sites to appraise its suitability as an injection model. Ten minipigs were sampled with tape strips and swabs and analysed by matrix-assisted laser desorption/ionization-time of flight mass spectrometry and 16S/ITS high throughput sequencing and confocal laser scanning microscopy. Results were directly compared with previous investigations of human injection sites. Pig skin was dominated by phyla 94.8% Firmicutes, 3% Proteobacteria, and 2.2% Actinobacteria. Staphylococcus spp. prevailed (44.4%) at the genus level with S. capitis and S. chromogenes present in all samples. Pig skin revealed populations in the 104 colony-forming units (CFU)/cm2 range with 3% identified as Gram-negative and increased alpha diversity (compared with 102 CFU/cm2 and 10% in humans). While notable taxonomical differences on species levels were seen, pig skin encompassed 97.1% of genera found in human samples. The increased population and variation found support the pig neck as an imperfect but fidelitous subcutaneous injection model that can adequately challenge devices from a microbial standpoint.

Prophylactic treatment of breast implants with a solution of gentamicin, vancomycin and cefazolin antibiotics for women undergoing breast reconstructive surgery: protocol for a randomised, double-blind, placebo-controlled trial (The BREAST-AB trial)

INTRODUCTION

Periprosthetic infection is one of the most severe complications following implant-based breast reconstruction affecting 5%-10% of the women. Currently, many surgeons apply antibiotics locally on the breast implant to reduce the risk of postoperative infection, but no randomised, placebo-controlled trials have tested the treatment's efficacy.

METHODS AND ANALYSIS

The BREAST-AB trial (BREAST-AntiBiotics) is an investigator-initiated, multicentre, randomised, placebo-controlled, double-blind trial of local treatment with gentamicin, vancomycin and cefazolin on breast implants in women undergoing implant-based breast reconstruction. The trial drug consists of 80 mg gentamicin, 1 g vancomycin and 1 g cefazolin dissolved in 500 mL of isotonic saline. The placebo solution consists of 500 mL isotonic saline. The trial drug is used to wash the dissected tissue pocket and the breast implant prior to insertion. The primary outcome is all-cause explantation of the breast implant within 180 days after the breast reconstruction surgery. This excludes cases where the implant is replaced with a new permanent implant, for example, for cosmetic reasons. Key long-term outcomes include capsular contracture and quality of life. The trial started on 26 January 2021 and is currently recruiting.

ETHICS AND DISSEMINATION

The trial was approved by the Regional Ethics Committee of the Capital Region (H-20056592) on 1 January 2021 and the Danish Medicines Agency (2020070016) on 2 August 2020. The main paper will include the primary and secondary outcomes and will be submitted to an international peer-reviewed journal.

TRIAL REGISTRATION NUMBER

NCT04731025.

Injection site microflora in persons with diabetes: why needle reuse is not associated with increased infections?

Needle reuse is a common practice and primary cause of customer compliance issues such as pain, bruising, clogging, injection site reactions (ISR), and associated lipodystrophy. This study aimed to characterize skin microflora at injection sites and establish microbial contamination of used pen injectors and needles. The second objective was to evaluate the risk of infections during typical and repeated subcutaneous injections. 50 participants with diabetes and 50 controls (n = 100) were sampled through tape strips and skin swabs on the abdomen and thigh for skin microflora. Used pen injectors and needles were collected after in‐home use and from the hospital after drug administration by health care professionals (HCPs). Samples were analyzed by conventional culture, matrix‐assisted laser desorption/ionization‐time of flight (MALDI‐TOF), mass spectrometry (MS), confocal laser scanning microscopy (CLSM), and 16S/ITS high throughput sequencing (HTS). A mathematical model simulated the risk of needle contamination during injections. Injection site populations were in 10² cells/cm² order, with increased viable bacteria and anaerobic bacteria on the skin in persons with diabetes (p = 0.05). Interpersonal variation dominated other factors such as sex or location. A higher prevalence of Staphylococcus aureus on abdominal skin was found in persons with diabetes than control skin (p ≤ 0.05). Most needles and cartridges (95% and 86%) contained no biological signal. The location of the device collection (hospital vs home‐use) and use regimen did not affect contamination. CLSM revealed scarcely populated skin microflora scattered in aggregates, diplo, or single cells. Our mathematical model demonstrated that penetrating bacteria colonies during subcutaneous injection is unlikely. These findings clarify the lack of documented skin infections from subcutaneous insulin injections in research. Furthermore, these results can motivate the innovation and development of durable, reusable injection systems with pharmacoeconomic value and a simplified and enhanced user experience for patients.

Transcriptomic fingerprint of bacterial infection in lower extremity ulcers

Clinicians and researchers utilize subjective, clinical classification systems to stratify lower extremity ulcer infections for treatment and research. The purpose of this study was to examine whether these clinical classifications are reflected in the ulcer's transcriptome. RNA sequencing (RNA‐seq) was performed on biopsies from clinically infected lower extremity ulcers (n = 44). Resulting sequences were aligned to the host reference genome to create a transcriptome profile. Differential gene expression analysis and gene ontology (GO) enrichment analysis were performed between ulcer severities as well as between sample groups identified by k‐means clustering. Lastly, a support vector classifier was trained to estimate clinical infection score or k‐means cluster based on a subset of genes. Clinical infection severity did not explain the major sources of variability among the samples and samples with the same clinical classification demonstrated high inter‐sample variability. High proportions of bacterial RNA were identified in some samples, which resulted in a strong effect on transcription and increased expression of genes associated with immune response and inflammation. K‐means clustering identified two clusters of samples, one of which contained all of the samples with high levels of bacterial RNA. A support vector classifier identified a fingerprint of 20 genes, including immune‐associated genes such as CXCL8, GADD45B, and HILPDA, which accurately identified samples with signs of infection via cross‐validation. This study identified a unique, host‐transcriptome signature in the presence of infecting bacteria, often incongruent with clinical infection‐severity classifications. This suggests that stratification of infection status based on a transcriptomic fingerprint may be useful as an objective classification method to classify infection severity, as well as a tool for studying host–pathogen interactions.

The gut microbiota can orchestrate the signaling pathways in colorectal cancer

Current evidence suggests that bacteria contribute to the development of certain cancers, such as colorectal cancer (CRC), partly by stimulating chronic inflammation. However, little is known about the bacterial impact on molecular pathways in CRC. Recent studies have demonstrated how specific bacteria can influence the major CRC-related pathways, i.e., Wnt, PI3K-Akt, MAPK, TGF-β, EGFR, mTOR, and p53. In order to advance the current understanding and facilitate the choice of pathways to investigate, we have systematically collected and summarized the current knowledge within bacterial altered major pathways in CRC. Several pro-tumorigenic and anti-tumorigenic bacterial species and their respective metabolites interfere with the major signaling pathways addressed in this review. Not surprisingly, some of these studies investigated known CRC drivers, such as Escherichia coli, Fusobacterium nucleatum, and Bacteroides fragilis. Interestingly, some metabolites produced by bacterial species typically considered pathogenic, e.g., Vibrio cholera, displayed anti-tumorigenic activities, emphasizing the caution needed when classifying healthy and unhealthy microorganisms. The results collectively emphasize the complexity of the relationship between the microbiota and the tumorigenesis of CRC, and future studies should verify these findings in more realistic models, such as organoids, which constitute a promising platform. Moreover, future trials should investigate the clinical potential of preventive modulation of the gut microbiota regarding CRC development.

Bacterial biofilms predominate in both acute and chronic human lung infections

Background

A basic paradigm of human infection is that acute bacterial disease is caused by fast growing planktonic bacteria while chronic infections are caused by slow-growing, aggregated bacteria, a phenomenon known as a biofilm. For lung infections, this paradigm has been thought to be supported by observations of how bacteria proliferate in well-established growth media in the laboratory—the gold standard of microbiology.

Objective

To investigate the bacterial architecture in sputum from patients with acute and chronic lung infections.

Methods

Advanced imaging technology was used for quantification and direct comparison of infection types on fresh sputum samples, thereby directly testing the acute versus chronic paradigm.

Results

In this study, we compared the bacterial lifestyle (planktonic or biofilm), growth rate and inflammatory response of bacteria in freshly collected sputum (n=43) from patient groups presenting with acute or chronic lung infections. We found that both acute and chronic lung infections are dominated by biofilms (aggregates of bacteria within an extracellular matrix), although planktonic cells were observed in both sample types. Bacteria grew faster in sputum from acute infections, but these fast-growing bacteria were enriched in biofilms similar to the architecture thought to be reserved for chronic infections. Cellular inflammation in the lungs was also similar across patient groups, but systemic inflammatory markers were only elevated in acute infections.

Conclusions

Our findings indicate that the current paradigm of equating planktonic with acute and biofilm with chronic infection needs to be revisited as the difference lies primarily in metabolic rates, not bacterial architecture.

Nitric-oxide-driven oxygen release in anoxic Pseudomonas aeruginosa

Denitrification supports anoxic growth of Pseudomonas aeruginosa in infections. Moreover, denitrification may provide oxygen (O₂) resulting from dismutation of the denitrification intermediate nitric oxide (NO) as seen in Methylomirabilis oxyfera. To examine the prevalence of NO dismutation we studied O₂ release by P. aeruginosa in airtight vials. P. aeruginosa rapidly depleted O₂ but NO supplementation generated peaks of O₂ at the onset of anoxia, and we demonstrate a direct role of NO in the O₂ release. However, we were not able to detect genetic evidence for putative NO dismutases.

The supply of endogenous O₂ at the onset of anoxia could play an adaptive role when P. aeruginosa enters anaerobiosis. Furthermore, O₂ generation by NO dismutation may be more widespread than indicated by the reports on the distribution of homologues genes. In general, NO dismutation may allow removal of nitrate by denitrification without release of the very potent greenhouse gas, nitrous oxide.

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Pseudomonas aeruginosa was found to release O₂ at the onset of anoxia

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Peaks of O₂ were amplified in a nitric oxide reductase (NOR) mutant

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The O₂ release was mediated by nitric oxide (NO)

Biofilms can act as plasmid reserves in the absence of plasmid specific selection

Plasmids facilitate rapid bacterial adaptation by shuttling a wide variety of beneficial traits across microbial communities. However, under non-selective conditions, maintaining a plasmid can be costly to the host cell. Nonetheless, plasmids are ubiquitous in nature where bacteria adopt their dominant mode of life - biofilms. Here, we demonstrate that biofilms can act as spatiotemporal reserves for plasmids, allowing them to persist even under non-selective conditions. However, under these conditions, spatial stratification of plasmid-carrying cells may promote the dispersal of cells without plasmids, and biofilms may thus act as plasmid sinks.

Dynamics of skin microbiota in shoulder surgery infections

Post-surgical infections arise due to various contributing factors. Most important is the presence of potential pathogenic microorganisms in the skin complemented by the patient´s health status. Cutibacterium acnes is commonly present in the pilosebaceous glands and hair follicle funnels in human skin. After surgical intervention, these highly prevalent, slow-growing bacteria can be found in the deeper tissues and in proximity of implants. C. acnes is frequently implicated in post-surgical infections, often resulting in the need for revision surgery. This review summarizes the current understanding of microbial dynamics in shoulder surgical infections. In particular, we shed light on the contribution of C. acnes to post-surgical shoulder infections as well as their colonization and immune-modulatory potential. Despite being persistently found in post-surgical tissues, C. acnes is often underestimated as a causative organism due to its slow growth and the inefficient detection methods. We discuss the role of the skin environment constituted by microbial composition and host cellular status in influencing C. acnes recolonization potential. Future mapping of the individual skin microbiome in shoulder surgery patients using advanced molecular methods would be a useful approach for determining the risk of post-operative infections.

The importance of understanding the infectious microenvironment

Standard doses of antibiotics do not efficiently treat chronic infections of the soft tissue and bone. In this Personal View, we advocate for improving treatment of these infections by taking the infectious microenvironment into account. The infectious microenvironment can cause sensitive bacteria to lose their susceptibility to antibiotics that are effective in standard laboratory susceptibility testing. We propose that bacteria behave substantially different in standard laboratory conditions than they do in actual infections. The infectious microenvironment could impose changes in growth and metabolic activity that result in increased protection against antibiotics. Therefore, we advocate that improved antibiotic treatment of chronic infection is achievable when antibiotics are recommended on the basis of susceptibility testing in relevant in vitro conditions that resemble actual infectious microenvironments. We recommend establishing knowledge of the relevant conditions of the chemical and physical composition of the infectious microenvironment. Recent advances in RNA sequencing, metabolomics, and microscopy have made it possible for the characterisation of the microenvironment of infections and to validate the clinical relevance of in vitro conditions to actual infections.

Measuring enzymatic degradation of degradable starch microspheres using confocal laser scanning microscopy

Degradable starch microspheres (DSM) have long been used for topical haemostasis, temporary vascular occlusion and as drug delivery systems. When used for the latter, exact degradation rates of DSM have high importance, as this ensures a controlled and timed drug delivery. Current methods of analysing degradation rates are based on whole batch measurements, which does not yield information regarding individual times of degradation nor does it provide direct correlation measurements between sphere diameter and specific degradation time. In this paper we present an alternative method for measuring degradation rates of biodegradable starch microspheres using confocal laser scanning microscopy (CLSM). We succeeded in visualizing the degradation by staining the DSM and then following the spheres over time in a confocal microscope, after the addition of α-amylase. Individual degradation rates of single spheres could be followed, allowing a precise correlation measure between sphere size and degradation time. Furthermore, physical abnormalities such as internal cavities were detected within some spheres. These physical differences also had a measurable effect on the rate of degradation. Finally, complete degradation rates could be determined very accurately. To our knowledge, this is the first paper in which DSM degradation is visualized and measured using CLSM. STATEMENT OF SIGNIFICANCE: Using degradable starch microspheres as a drug delivery system, is a continuously evolving field which shows promise in several different areas of illnesses. This paper presents a new method which visualizes enzymatic degradation of starch microspheres in real-time using confocal microscopy. The method is simple, yet the versatility of it suggests that it could be broadly applied within the field of biodegradation. Here, it illuminates a previously uninvestigated parameter: the effect of physical sphere deformities on the rate of degradation. It also provides precise correlation measures between initial sphere size and time of complete degradation.

The impact of mental models on the treatment and research of chronic infections due to biofilms

Research on biofilms is predominantly made in in vitro contexts. However, in vivo observation of biofilms in human chronic infections shows distinct differences compared to in vitro biofilm growth. This could imply the use of an inadequate mental model both in research and healthcare practices. Drawing on knowledge from the cognitive sciences, we hypothesise that the predominance of in vitro research on biofilms is skewed towards a mental model promoting wrong inferences for researchers and healthcare professionals (HCPs) in the in vivo context. To explore the prevalence of such a mental model, we carried out a qualitative image analysis in which biofilm illustrations from a Google image search were coded for typical in vitro or in vivo characteristics. Further, to investigate potential misinformed and unhelpful clinical interventions related to biofilms, we conducted a quantitative questionnaire among HCPs. The questions were designed to test whether knowledge about in vitro biofilms was used in an in vivo context. This questionnaire was analysed through a chi-squared test. Most biofilm illustrations were consistent with the in vitro model. A statistical analysis of survey responses revealed that HCPs have adequate knowledge about biofilm but often respond incorrectly when asked to apply their knowledge to in vivo contexts. The outcome of this research points to a prevalent and consolidated mental model derived from in vitro observations. This model has likely been made dominant by HCPs' frequent exposure to visual depictions in articles and presentations. The prevalence of the in vitro model sets up the possibility of erroneous claims when the in vitro model is inadequately applied to in vivo contexts. This has potential implications for HCPs working in fields involving biofilm, such as wound care treatment.

A novel chronic wound biofilm model sustaining coexistence of Pseudomonas aeruginosa and Staphylococcus aureus suitable for testing of antibiofilm effect of antimicrobial solutions and wound dressings

Chronic wounds are a large burden to patients and healthcare systems. Biofilm infections in chronic wounds are crucial factors leading to non‐healing of wounds. It is important to study biofilm in wounds and to develop effective interventions against wound biofilm. This study presents a novel in vitro biofilm model mimicking infected chronic wounds. The novel layered chronic wound biofilm model uses woundlike media and includes both Pseudomonas aeruginosa and Staphylococcus aureus, which have been identified as the most important pathogens in wounds. The model sustains their coexistence for at least 96 h. Microscopy of the model revealed microbial growth in non‐surface attached microcolonies as previously observed in vivo. The model was used to determine log₁₀‐reduction for the use of an antimicrobial solution and antimicrobial dressings (containing silver or honey) showing moderate‐to‐low antibiofilm effect, which indicates better concordance with the observed clinical performance of this type of treatment than other widely used standard tests.