The 2023 Orthopedic Research Society's international consensus meeting on musculoskeletal infection: Summary from the in vitro section

Antimicrobial strategies for musculoskeletal infections are typically first developed with in vitro models. The In Vitro Section of the 2023 Orthopedic Research Society Musculoskeletal Infection international consensus meeting (ICM) probed our state of knowledge of in vitro systems with respect to bacteria and biofilm phenotype, standards, in vitro activity, and the ability to predict in vivo efficacy. A subset of ICM delegates performed systematic reviews on 15 questions and made recommendations and assessment of the level of evidence that were then voted on by 72 ICM delegates. Here, we report recommendations and rationale from the reviews and the results of the internet vote. Only two questions received a ≥90% consensus vote, emphasizing the disparate approaches and lack of established consensus for in vitro modeling and interpretation of results. Comments on knowledge gaps and the need for further research on these critical MSKI questions are included.

Improving antimicrobial treatment in terms of antimicrobial stewardship and health costs by an OPAT service

PURPOSE

Outpatient parenteral antimicrobial therapy (OPAT) is a standard for antimicrobial therapy internationally. With this prospective cohort study, we aimed to assess the impact of an OPAT service as part of antimicrobial stewardship (AMS) and evaluate the safety and efficiency of the program while illuminating the financial benefit for the hospital.

METHODS

Socio-demographic data, treatment regimen and outcomes were prospectively recorded for all patients assigned to the program of the OPAT unit of the University Hospital of Zurich between November 2018 and September 2022.

RESULTS

In total, we recorded 303 OPAT assignments of which 260 resulted in effective OPAT episodes. The 260 OPAT episodes were further optimized toward the choice of antimicrobial agent (n = 18) and length of therapy (n = 6). Moreover, OPAT resulted in alteration of patient assessment and care led by AMS strategies in 247 of 260 episodes (95%). While the bed days saved per year increased consistently with time, a total of 3934 in-hospital treatment days were saved amounting to a cost saving of 9,835,000 CHF over 47 months. Adverse events were recorded in 46 cases whilst only two of these have been the reason for readmission during OPAT treatment. Clinical cure was noted in 77% (199/260) and was negatively associated with Charlson Comorbidity Index (CCI; OR per 1 unit higher 0.85 (95% CI 0.78-0.93)).

CONCLUSION

This study demonstrates the impact of an OPAT service in the framework of AMS as well as its benefits for the hospital whilst preserving safety and efficacy for the patient's parenteral antimicrobial treatment.

MEndoB, a chimeric lysin featuring a novel domain architecture and superior activity for the treatment of staphylococcal infections

Bacterial infections are a growing global healthcare concern, as an estimated annual 4.95 million deaths are associated with antimicrobial resistance (AMR). Methicillin-resistant Staphylococcus aureus is one of the deadliest pathogens and a high-priority pathogen according to the World Health Organization. Peptidoglycan hydrolases (PGHs) of phage origin have been postulated as a new class of antimicrobials for the treatment of bacterial infections, with a novel mechanism of action and no known resistances. The modular architecture of PGHs permits the creation of chimeric PGH libraries. In this study, the chimeric enzyme MEndoB was selected from a library of staphylococcal PGHs based on its rapid and sustained activity against staphylococci in human serum. The benefit of the presented screening approach was illustrated by the superiority of MEndoB in a head-to-head comparison with other PGHs intended for use against staphylococcal bacteremia. MEndoB displayed synergy with antibiotics and rapid killing in human whole blood with complete inhibition of re-growth over 24 h at low doses. Successful treatment of S. aureus-infected zebrafish larvae with MEndoB provided evidence for its in vivo effectiveness. This was further confirmed in a lethal systemic mouse infection model in which MEndoB significantly reduced S. aureus loads and tumor necrosis factor alpha levels in blood in a dose-dependent manner, which led to increased survival of the animals. Thus, the thorough lead candidate selection of MEndoB resulted in an outstanding second-generation PGH with in vitro, ex vivo, and in vivo results supporting further development.IMPORTANCEOne of the most pressing challenges of our era is the rising occurrence of bacteria that are resistant to antibiotics. Staphylococci are prominent pathogens in humans, which have developed multiple strategies to evade the effects of antibiotics. Infections caused by these bacteria have resulted in a high burden on the health care system and a significant loss of lives. In this study, we have successfully engineered lytic enzymes that exhibit an extraordinary ability to eradicate staphylococci. Our findings substantiate the importance of meticulous lead candidate selection to identify therapeutically promising peptidoglycan hydrolases with unprecedented activity. Hence, they offer a promising new avenue for treating staphylococcal infections.

In Vitro Assessment of Bacterial Adhesion and Biofilm Formation on Novel Bioactive, Biodegradable Electrospun Fiber Meshes Intended to Support Tendon Rupture Repair

The surgical repair of a ruptured tendon faces two major problems: specifically increased fibrous adhesion to the surrounding tissue and inferior mechanical properties of the scar tissue compared to the native tissue. Bacterial attachment to implant materials is an additional problem as it might lead to severe infections and impaired recovery. To counteract adhesion formation, two novel implant materials were fabricated by electrospinning, namely, a random fiber mesh containing hyaluronic acid (HA) and poly(ethylene oxide) (PEO) in a ratio of 1:1 (HA/PEO 1:1) and 1:4 (HA/PEO 1:4), respectively. Electrospun DegraPol (DP) treated with silver nanoparticles (DP-Ag) was developed to counteract the bacterial attachment. The three novel materials were compared to the previously described DP and DP with incorporated insulin-like growth factor-1 (DP-IGF-1), two implant materials that were also designed to improve tendon repair. To test whether the materials are prone to bacterial adhesion and biofilm formation, we assessed 10 strains of Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Enterococcus faecalis, known for causing nosocomial infections. Fiber diameter, pore size, and water contact angle, reflecting different degrees of hydrophobicity, were used to characterize all materials. Generally, we observed higher biofilm formation on the more hydrophobic DP as compared to the more hydrophilic DP-IGF-1 and a trend toward reduced biofilm formation for DP treated with silver nanoparticles. For the two HA/PEO implants, a similar biofilm formation was observed. All tested materials were highly prone to bacterial adherence and biofilm formation, pointing toward the need of further material development, including the optimized incorporation of antibacterial agents such as silver nanoparticles or antibiotics.

Impact of sex and gender on post-COVID-19 syndrome, Switzerland, 2020

BackgroundWomen are overrepresented among individuals with post-acute sequelae of SARS-CoV-2 infection (PASC). Biological (sex) as well as sociocultural (gender) differences between women and men might account for this imbalance, yet their impact on PASC is unknown.AimWe assessed the impact of sex and gender on PASC in a Swiss population.MethodOur multicentre prospective cohort study included 2,856 (46% women, mean age 44.2 ± 16.8 years) outpatients and hospitalised patients with PCR-confirmed SARS-CoV-2 infection.ResultsAmong those who remained outpatients during their first infection, women reported persisting symptoms more often than men (40.5% vs 25.5% of men; p < 0.001). This sex difference was absent in hospitalised patients. In a crude analysis, both female biological sex (RR = 1.59; 95% CI: 1.41-1.79; p < 0.001) and a score summarising gendered sociocultural variables (RR = 1.05; 95% CI: 1.03-1.07; p < 0.001) were significantly associated with PASC. Following multivariable adjustment, biological female sex (RR = 0.96; 95% CI: 0.74-1.25; p = 0.763) was outperformed by feminine gender-related factors such as a higher stress level (RR = 1.04; 95% CI: 1.01-1.06; p = 0.003), lower education (RR = 1.16; 95% CI: 1.03-1.30; p = 0.011), being female and living alone (RR = 1.91; 95% CI: 1.29-2.83; p = 0.001) or being male and earning the highest income in the household (RR = 0.76; 95% CI: 0.60-0.97; p = 0.030).ConclusionSpecific sociocultural parameters that differ in prevalence between women and men, or imply a unique risk for women, are predictors of PASC and may explain, at least in part, the higher incidence of PASC in women. Once patients are hospitalised during acute infection, sex differences in PASC are no longer evident.

C-di-AMP levels modulate Staphylococcus aureus cell wall thickness, response to oxidative stress, and antibiotic resistance and tolerance

IMPORTANCE

Antibiotic resistance and tolerance are substantial healthcare-related problems, hampering effective treatment of bacterial infections. Mutations in the phosphodiesterase GdpP, which degrades cyclic di-3', 5'-adenosine monophosphate (c-di-AMP), have recently been associated with resistance to beta-lactam antibiotics in clinical Staphylococcus aureus isolates. In this study, we show that high c-di-AMP levels decreased the cell size and increased the cell wall thickness in S. aureus mutant strains. As a consequence, an increase in resistance to cell wall targeting antibiotics, such as oxacillin and fosfomycin as well as in tolerance to ceftaroline, a cephalosporine used to treat methicillin-resistant S. aureus infections, was observed. These findings underline the importance of investigating the role of c-di-AMP in the development of tolerance and resistance to antibiotics in order to optimize treatment in the clinical setting.

Single-cell patterning and characterisation of antibiotic persistent bacteria using bio-sCAPA

In microbiology, accessing single-cell information within large populations is pivotal. Here we introduce bio-sCAPA, a technique for patterning bacterial cells in defined geometric arrangements and monitoring their growth in various nutrient environments. We demonstrate bio-sCAPA with a study of subpopulations of antibiotic-tolerant bacteria, known as persister cells, which can survive exposure to high doses of antibiotics despite lacking any genetic resistance to the drug. Persister cells are associated with chronic and relapsing infections, yet are difficult to study due in part to a lack of scalable, single-cell characterisation methods. As >105 cells can be patterned on each template, and multiple templates can be patterned in parallel, bio-sCAPA allows for very rare population phenotypes to be monitored with single-cell precision across various environmental conditions. Using bio-sCAPA, we analysed the phenotypic characteristics of single Staphylococcus aureus cells tolerant to flucloxacillin and rifampicin killing. We find that antibiotic-tolerant S. aureus cells do not display significant heterogeneity in growth rate and are instead characterised by prolonged lag-time phenotypes alone.

Systemic application of bone-targeting peptidoglycan hydrolases as a novel treatment approach for staphylococcal bone infection

IMPORTANCE

The rising prevalence of antimicrobial resistance in S. aureus has rendered treatment of staphylococcal infections increasingly difficult, making the discovery of alternative treatment options a high priority. Peptidoglycan hydrolases, a diverse group of bacteriolytic enzymes, show high promise as such alternatives due to their rapid and specific lysis of bacterial cells, independent of antibiotic resistance profiles. However, using these enzymes for the systemic treatment of local infections, such as osteomyelitis foci, needs improvement, as the therapeutic distributes throughout the whole host, resulting in low concentrations at the actual infection site. In addition, the occurrence of intracellularly persisting bacteria can lead to relapsing infections. Here, we describe an approach using tissue-targeting to increase the local concentration of therapeutic enzymes in the infected bone. The enzymes were modified with a short targeting moiety that mediated accumulation of the therapeutic in osteoblasts and additionally enables targeting of intracellularly surviving bacteria.

Mechanisms and clinical relevance of the bidirectional relationship of viral infections with metabolic diseases

Viruses have been present during all evolutionary steps on earth and have had a major effect on human history. Viral infections are still among the leading causes of death. Another public health concern is the increase of non-communicable metabolic diseases in the last four decades. In this Review, we revisit the scientific evidence supporting the presence of a strong bidirectional feedback loop between several viral infections and metabolic diseases. We discuss how viruses might lead to the development or progression of metabolic diseases and conversely, how metabolic diseases might increase the severity of a viral infection. Furthermore, we discuss the clinical relevance of the current evidence on the relationship between viral infections and metabolic disease and the present and future challenges that should be addressed by the scientific community and health authorities.

An intensive care unit outbreak with multi-drug-resistant Pseudomonas aeruginosa - spotlight on sinks

BACKGROUND

Pseudomonas aeruginosa and other Gram-negative bacteria have the ability to persist in moist environments in healthcare settings, but their spread from these areas can result in outbreaks of healthcare-associated infections.

METHODS

This study reports the investigation and containment of a multi-drug-resistant P. aeruginosa outbreak in three intensive care units of a Swiss university hospital. In total, 255 patients and 276 environmental samples were screened for the multi-drug-resistant P. aeruginosa outbreak strain. The environmental sampling and molecular characterization of patient and environmental strains, and control strategies implemented, including waterless patient care, are described.

RESULTS

Between March and November 2019, the outbreak affected 29 patients. Environmental sampling detected the outbreak strain in nine samples of sink siphons of three different intensive care units with a common water sewage system, and on one gastroscope. Three weeks after replacement of the sink siphons, the outbreak strain re-grew in siphon-derived samples and newly affected patients were identified. The outbreak ceased after removal of all sinks in the proximity of patients and in medication preparation areas, and minimization of tap water use. Multi-locus sequence typing indicated clonality (sequence type 316) in 28/29 patient isolates and all 10 environmental samples.

CONCLUSIONS

Sink removal combined with the introduction of waterless patient care terminated the multi-drug-resistant P. aeruginosa outbreak. Sinks in intensive care units may pose a risk for point source outbreaks with P. aeruginosa and other bacteria persisting in moist environments.

Limited Adaptation of Staphylococcus aureus during Transition from Colonization to Invasive Infection

Staphylococcus aureus carriage is a risk factor for invasive infections. Unique genetic elements favoring the transition from colonizing to invasive phenotype have not yet been identified, and phenotypic adaptation traits are understudied. We therefore assessed phenotypic and genotypic profiles of 11 S. aureus isolate pairs sampled from colonized patients simultaneously suffering from invasive S. aureus infections. Ten out of 11 isolate pairs displayed the same spa and multilocus sequence type, suggesting colonization as an origin for the invasive infection. Systematic analysis of colonizing and invasive isolate pairs showed similar adherence, hemolysis, reproductive fitness properties, antibiotic tolerance, and virulence in a Galleria mellonella infection model, as well as minimal genetic differences. Our results provide insights into the similar phenotypes associated with limited adaptation between colonizing and invasive isolates. Disruption of the physical barriers of mucosa or skin was identified in the majority of patients, further emphasizing colonization as a major risk factor for invasive disease. IMPORTANCE S. aureus is a major pathogen of humans, causing a wide range of diseases. The difficulty to develop a vaccine and antibiotic treatment failure warrant the exploration of novel treatment strategies. Asymptomatic colonization of the human nasal passages is a major risk factor for invasive disease, and decolonization procedures have been effective in preventing invasive infections. However, the transition of S. aureus from a benign colonizer of the nasal passages to a major pathogen is not well understood, and both host and bacterial properties have been discussed as being relevant for this behavioral change. We conducted a thorough investigation of patient-derived strain pairs reflecting colonizing and invasive isolates in a given patient. Although we identified limited genetic adaptation in certain strains, as well as slight differences in adherence capacity among colonizing and invasive isolates, our work suggests that barrier breaches are a key event in the disease continuum of S. aureus.

Rapid antimicrobial susceptibility testing in patients with bacteraemia due to Enterobacterales: an implementation study

AIMS OF THE STUDY

The goal of this descriptive study was to assess the performance as well as the extent of the clinical impact of rapid automated antimicrobial susceptibility testing in patients with bacteraemia due to Enterobacterales. We also aimed to analyse how rapid automated antimicrobial susceptibility testing influences clinical decision-making.

METHODS

This single-centre study conducted at the University Hospital of Zurich included data from all consecutive patients with Enterobacterales bacteraemia from November 2019 to October 2020. There was no control group. The primary outcome was the effect of rapid automated antimicrobial susceptibility testing on antibiotic therapy (no adjustment, escalation to a broader-spectrum antibiotic or de-escalation to a narrower-spectrum antibiotic). Rapid automated antimicrobial susceptibility testing results were further compared to susceptibility tests using European Committee on Antimicrobial Susceptibility Testing (EUCAST) standard methods and erroneous results were noted. Additionally, we investigated turnaround times for rapid automated antimicrobial susceptibility testing and routine diagnostic testing.

RESULTS

We analysed 106 patients with 116 episodes of bacteraemia due to Enterobacterales, with Escherichia coli and Klebsiella pneumoniae being the most frequent isolates. Almost 8% of pathogens were multidrug resistant. Rapid automated antimicrobial susceptibility testing showed category agreement in 98.4% of all interpretable cases. A significant reduction of more than 20 h in turnaround times could be achieved with rapid automated antimicrobial susceptibility testing compared to the routine diagnostic workflow. In the majority of cases, rapid automated antimicrobial susceptibility testing had no effect, given that the empirical therapy was already correct or circumstances did not allow for de-escalation. In 38.8% of cases, antimicrobial therapy was adjusted, whereas eight cases were de-escalated based on rapid automated antimicrobial susceptibility testing alone.

CONCLUSIONS

Rapid automated antimicrobial susceptibility testing may be a valuable and safe way to accelerate diagnosis. In particular, time to suitable therapy can be shortened in cases of incorrect therapy. However, physicians are reluctant to de-escalate antibiotic therapy based on rapid automated antimicrobial susceptibility testing alone, limiting its impact in everyday clinics. To further explore the potential of rapid automated antimicrobial susceptibility testing, a stringent/compulsory antibiotic stewardship programme would be a valuable next step.

Serine-threonine phosphoregulation by PknB and Stp contributes to quiescence and antibiotic tolerance in Staphylococcus aureus

Staphylococcus aureus can cause infections that are often chronic and difficult to treat, even when the bacteria are not antibiotic resistant because most antibiotics act only on metabolically active cells. Subpopulations of persister cells are metabolically quiescent, a state associated with delayed growth, reduced protein synthesis, and increased tolerance to antibiotics. Serine-threonine kinases and phosphatases similar to those found in eukaryotes can fine-tune essential bacterial cellular processes, such as metabolism and stress signaling. We found that acid stress-mimicking conditions that S. aureus experiences in host tissues delayed growth, globally altered the serine and threonine phosphoproteome, and increased threonine phosphorylation of the activation loop of the serine-threonine protein kinase B (PknB). The deletion of stp, which encodes the only annotated functional serine-threonine phosphatase in S. aureus, increased the growth delay and phenotypic heterogeneity under different stress challenges, including growth in acidic conditions, the intracellular milieu of human cells, and abscesses in mice. This growth delay was associated with reduced protein translation and intracellular ATP concentrations and increased antibiotic tolerance. Using phosphopeptide enrichment and mass spectrometry-based proteomics, we identified targets of serine-threonine phosphorylation that may regulate bacterial growth and metabolism. Together, our findings highlight the importance of phosphoregulation in mediating bacterial quiescence and antibiotic tolerance and suggest that targeting PknB or Stp might offer a future therapeutic strategy to prevent persister formation during S. aureus infections.

Antibiotic prophylaxis before dental procedures to prevent infective endocarditis: a systematic review

PURPOSE

Infective endocarditis (IE) is a severe bacterial infection. As a measure of prevention, the administration of antibiotic prophylaxis (AP) prior to dental procedures was recommended in the past. However, between 2007 and 2009, guidelines for IE prophylaxis changed all around the word, limiting or supporting the complete cessation of AP. It remains unclear whether AP is effective or not against IE.

METHODS

We conducted a systematic review whether the administration of AP in adults before any dental procedure, compared to the non-administration of such drugs, has an effect on the risk of developing IE. We searched for studies in the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE via OVID, and EMBASE. Two different authors filtered articles independently and data extraction was performed based on a pre-defined protocol.

RESULTS

The only cohort study meeting our criteria included patients at high-risk of IE. Analysis of the extracted data showed a non-significant decrease in the risk of IE when high-risk patients take AP prior to invasive dental procedures (RR 0.39, p-value 0.11). We did not find other studies including patients at low or moderate risk of IE. Qualitative evaluation of the excluded articles reveals diversity of results and suggests that most of the state-of-the-art articles are underpowered.

CONCLUSIONS

Evidence to support or discourage the use of AP prior to dental procedures as a prevention for IE is very low. New high-quality studies are needed, even though such studies would require big settings and might not be immediately feasible.

Antibacterial Neutrophil Effector Response: Ex Vivo Quantification of Regulated Cell Death Associated with Extracellular Trap Release

Regulated cell death (RCD) and the concomitant release of extracellular traps by neutrophils (NETs) constitute an important antibacterial effector response. Usually, the dynamic processes of RCD and NETs release are assessed independently of each other by either unspecific or time-consuming methods. Here, we describe a flow cytometry-based high-throughput analysis method incorporating neutrophil RCD and NETs release with visual live-imaging conformation upon ex vivo bacterial challenge. This combined approach allows to quantify and closely follow the kinetics of the dynamic neutrophil effector response towards bacterial infection.

A retrospective analysis of blood culture-negative endocarditis at a tertiary care centre in Switzerland

AIMS OF THE STUDY

Numerous studies from different countries have contributed to an improved understanding of blood culture-negative infective endocarditis. However, little is known about its epidemiology and microbiology in Switzerland. We aimed to assess the epidemiology and microbiology of blood culture-negative endocarditis at the University Hospital Zurich, Switzerland.

METHODS

We screened all patients hospitalised between 1997 and 2020 with possible or definite endocarditis at our institution. Thereof, we identified all cases with blood culture-negative endocarditis and retrospectively retrieved patient characteristics, microbiological, histopathological, radiographic and surgical data from medical records.

RESULTS

Among 861 patients screened, 66 (7.7%) cases of blood culture-negative endocarditis were identified. Thereof, 31 cases could be microbiologically documented or not documented (n = 30), and in five cases a non-infectious aetiology was confirmed. Endocarditis predominantly affected men (77%) and the left heart (79%); predisposing factors were prosthetic valves (42%), congenital heart disease (35%) and prior endocarditis (14%). The most common reasons for negative blood cultures were antibiotic treatment prior to blood culture sampling (35%), fastidious and slow growing microorganisms (30%) and definite non-infective endocarditis (8%). Coxiella burnetii and Bartonella spp. were the most common fastidious bacteria identified. In addition to serology, identification of causative microorganisms was possible by microbiological and/or histopathological analysis of tissue samples, of which polymerase chain reaction testing (PCR) of the 16S ribosomal RNA proved to be most successful.

CONCLUSIONS

The present study provides a detailed analysis of blood culture-negative endocarditis over a time span of more than 20 years in Zurich, Switzerland. Antibiotic treatment prior to blood collection, and fastidious and slow growing organisms were identified as main reasons for sterile blood cultures. Typical culture-negative bacteria were mainly found by PCR and/or culture of tissue samples.

Development and validation of a prognostic model for the early identification of COVID-19 patients at risk of developing common long COVID symptoms

BACKGROUND

The coronavirus disease 2019 (COVID-19) pandemic demands reliable prognostic models for estimating the risk of long COVID. We developed and validated a prediction model to estimate the probability of known common long COVID symptoms at least 60 days after acute COVID-19.

METHODS

The prognostic model was built based on data from a multicentre prospective Swiss cohort study. Included were adult patients diagnosed with COVID-19 between February and December 2020 and treated as outpatients, at ward or intensive/intermediate care unit. Perceived long-term health impairments, including reduced exercise tolerance/reduced resilience, shortness of breath and/or tiredness (REST), were assessed after a follow-up time between 60 and 425 days. The data set was split into a derivation and a geographical validation cohort. Predictors were selected out of twelve candidate predictors based on three methods, namely the augmented backward elimination (ABE) method, the adaptive best-subset selection (ABESS) method and model-based recursive partitioning (MBRP) approach. Model performance was assessed with the scaled Brier score, concordance c statistic and calibration plot. The final prognostic model was determined based on best model performance.

RESULTS

In total, 2799 patients were included in the analysis, of which 1588 patients were in the derivation cohort and 1211 patients in the validation cohort. The REST prevalence was similar between the cohorts with 21.6% (n = 343) in the derivation cohort and 22.1% (n = 268) in the validation cohort. The same predictors were selected with the ABE and ABESS approach. The final prognostic model was based on the ABE and ABESS selected predictors. The corresponding scaled Brier score in the validation cohort was 18.74%, model discrimination was 0.78 (95% CI: 0.75 to 0.81), calibration slope was 0.92 (95% CI: 0.78 to 1.06) and calibration intercept was -0.06 (95% CI: -0.22 to 0.09).

CONCLUSION

The proposed model was validated to identify COVID-19-infected patients at high risk for REST symptoms. Before implementing the prognostic model in daily clinical practice, the conduct of an impact study is recommended.

Antibody response to a third SARS‐CoV‐2 vaccine dose in recipients of an allogeneic haematopoietic cell transplantation

Allogeneic haematopoietic cell transplantation (allo-HCT) recipients show impaired antibody (Ab) response to a standard two-dose vaccination against severe acute respiratory syndrome coronavirus-2 and currently a third dose is recommended as part of the primary vaccination regimen. By assessing Ab titres 1 month after a third mRNA vaccine dose in 74 allo-HCT recipients we show sufficient neutralisation activity in 77% of the patients. Discontinuation of immunosuppression before the third vaccine led to serological responses in 50% of low responders to two vaccinations. Identifying factors that might contribute to better vaccine responses in allo-HCT recipients is critical to optimise current vaccination strategies.

Rapid detection of Staphylococcus aureus and Streptococcus pneumoniae by real-time analysis of volatile metabolites

Early detection of pathogenic bacteria is needed for rapid diagnostics allowing adequate and timely treatment of infections. In this study, we show that secondary electrospray ionization–high resolution mass spectrometry (SESI-HRMS) can be used as a diagnostic tool for rapid detection of bacterial infections as a supportive system for current state-of-the-art diagnostics. Volatile organic compounds (VOCs) produced by growing S. aureus or S. pneumoniae cultures on blood agar plates were detected within minutes and allowed for the distinction of these two bacteria on a species and even strain level within hours. Furthermore, we obtained a fingerprint of clinical patient samples within minutes of measurement and predominantly observed a separation of samples containing live bacteria compared to samples with no bacterial growth. Further development of this technique may reduce the time required for microbiological diagnosis and should help to improve patient’s tailored treatment.

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Real-time mass spectrometry shows potential as a tool for microbiological diagnosis

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Bacterial volatile metabolites from 1 × 10³ CFUs are detected within minutes

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S. aureus and S. pneumoniae can be distinguished on species and even strain level

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Complex clinical samples cluster according to presence or absence of viable bacteria

The group A Streptococcus interleukin-8 protease SpyCEP promotes bacterial intracellular survival by evasion of autophagy

Autophagy serves an innate immune function in defending the host against invading bacteria, including group A Streptococcus (GAS). Autophagy is regulated by numerous host proteins, including the endogenous negative regulator calpain, a cytosolic protease. Globally disseminated serotype M1T1 GAS strains associated with high invasive disease potential express numerous virulence factors and resist autophagic clearance. Upon in vitro infection of human epithelial cell lines with representative wild-type GAS M1T1 strain 5448 (M1.5448), we observed increased calpain activation linked to a specific GAS virulence factor, the IL-8 protease SpyCEP. Calpain activation inhibited autophagy and decreased capture of cytosolic GAS in autophagosomes. In contrast, the serotype M6 GAS strain JRS4 (M6.JRS4), which is highly susceptible to host autophagy-mediated killing, expresses low levels of SpyCEP and does not activate calpain. Overexpression of SpyCEP in M6.JRS4 stimulated calpain activation, inhibited autophagy and significantly decreased bacterial capture in autophagosomes. These paired loss- and gain-of-function studies reveal a novel role for the bacterial protease SpyCEP in enabling GAS M1 evasion of autophagy and host innate immune clearance.

Intervertebral disc cell chondroptosis elicits neutrophil response in Staphylococcus aureus spondylodiscitis

To understand the pathophysiology of spondylodiscitis due to Staphylococcus aureus, an emerging infectious disease of the intervertebral disc (IVD) and vertebral body with a high complication rate, we combined clinical insights and experimental approaches. Clinical data and histological material of nine patients suffering from S. aureus spondylodiscitis were retrospectively collected at a single center. To mirror the clinical findings experimentally, we developed a novel porcine ex vivo model mimicking acute S. aureus spondylodiscitis and assessed the interaction between S. aureus and IVD cells within their native environment. In addition, the inflammatory features underlying this interaction were assessed in primary human IVD cells. Finally, mirroring the clinical findings, we assessed primary human neutrophils for their ability to respond to secreted inflammatory modulators of IVD cells upon the S. aureus challenge. Acute S. aureus spondylodiscitis in patients was characterized by tissue necrosis and neutrophil infiltration. Additionally, the presence of empty IVD cells’ lacunae was observed. This was mirrored in the ex vivo porcine model, where S. aureus induced extensive IVD cell death, leading to empty lacunae. Concomitant engagement of the apoptotic and pyroptotic cell death pathways was observed in primary human IVD cells, resulting in cytokine release. Among the released cytokines, functionally intact neutrophil-priming as well as broad pro- and anti-inflammatory cytokines which are known for their involvement in IVD degeneration were found. In patients as well as ex vivo in a novel porcine model, S. aureus IVD infection caused IVD cell death, resulting in empty lacunae, which was accompanied by the release of inflammatory markers and recruitment of neutrophils. These findings offer valuable insights into the important role of inflammatory IVD cell death during spondylodiscitis and potential future therapeutic approaches.