Given the accelerating appearance of antimicrobial resistance, there is an urgent need for more fundamental research into novel antibiotic strategies. The work in this thesis helps to address this... Show moreGiven the accelerating appearance of antimicrobial resistance, there is an urgent need for more fundamental research into novel antibiotic strategies. The work in this thesis helps to address this global problem by developing new antibiotic compounds, inspired by the antibacterial mechanisms of the natural antibiotic bacitracin. By unravelling the unique mechanism of action that bacitracin employs, we discovered that the inclusion of a small hydrophobic group in key locations of the molecule results in a dramatic enhancement of antibacterial activity, in some cases more than 100 times more potent than bacitracin. Crucially we found that the most potent analogues are particularly active against antibiotic-resistant bacteria including those bearing clinically challenging resistance genes. In doing so we have developed potent next-generation variants of this classic antibiotic and have taken important steps in the fight against antimicrobial resistance. Show less
Antimicrobial peptides (AMPs) are promising alternatives to antibiotics for treatment of antimicrobial resistant (AMR) bacterial infections. However, their narrow therapeutic window due to in vivo... Show moreAntimicrobial peptides (AMPs) are promising alternatives to antibiotics for treatment of antimicrobial resistant (AMR) bacterial infections. However, their narrow therapeutic window due to in vivo toxicity and limited stability hampers their clinical use. Here, we evaluated encapsulation of two amphiphilic AMPs, SAAP-148 and snake cathelicidin Ab-Cath, into oleyl-modified hyaluronic acid (OL-HA) nanogels to improve their selectivity index. The AMP-loaded OL-HA nanogels ranged 181–206 nm in size with a PDI of 0.2, highly negative surface charge (−47 to −48 mV) and moderate encapsulation efficiency (53–63%). The AMP-loaded OL-HA nanogels displayed similar activity in vitro as AMP solutions against AMR Staphylococcus aureus and Acinetobacter baumannii, with a dose-dependent effect over time. Importantly, the AMP-loaded OL-HA nanogels showed decreased cytotoxicity towards human erythrocytes and primary skin fibroblast, thereby improving the selectivity index of SAAP-148 and Ab-Cath by 2- and 16.8-fold, respectively. Particularly, the selectivity of Ab-Cath-loaded OL-HA nanogels has great clinical potential, with an index that reached ≥ 300 for S. aureus and ≥ 3000 for A. baumannii. These findings indicate that OL-HA nanogels are a promising drug delivery system to reduce the cytotoxicity of AMPs without substantially affecting their antimicrobial activity, thereby increasing their selectivity index and potential as therapeutics to combat AMR bacterial infections. Show less
The investigations described in this thesis lay out strategies aimed at advancing antibiotic research and development. The examples presented revolve around two main approaches: understanding drug... Show moreThe investigations described in this thesis lay out strategies aimed at advancing antibiotic research and development. The examples presented revolve around two main approaches: understanding drug-target interactions and target identification.Applications of microcalorimetry provide insights into the binding mechanism of known antibiotics and their target within the bacterial membranes. These studies provided the thermodynamic characterization of cell-wall active compounds and their cell-wall precursor or phospholipid targets.Furthermore, by repurposing a small molecule library in a microbial susceptibility screen, the discovery of two new antibiotic leads is described. A suite of target identification methods, including whole genome sequencing and MS-based chemical proteomics, led to the characterization of their mode of action. Structure activity optimization of the leads led to the discovery of a new class of DNA gyrase inhibitors, acting on a so-far unexploited site of this validated bacterial target, as well as the identification of previously unmapped pathways in S. aureus, orchestrated by series of known and unknown enzymes. Show less
The results described in this thesis expand and deepen the knowledge of the disease burden that several groups of Dutch travelers can face while traveling abroad and after returning home, varying... Show moreThe results described in this thesis expand and deepen the knowledge of the disease burden that several groups of Dutch travelers can face while traveling abroad and after returning home, varying from young medical students to the older traveler. One can think of communicable diseases (e.g. enteric- and respiratory infections), non-communicable diseases (e.g. exacerbation of cardiovascular diseases or mental disorders) and (road-traffic-related) injuries. In addition, travelers can also face non-medical challenges such as culture shock and violence. Travelers can also become colonized with resistant bacteria (e.g. ESBL-E) while staying abroad. Active surveillance and contact isolation precautions may then be recommended when a traveler returns from a destination in Asia, and is admitted to the hospital in the home country. The different studies provide more insights and practical advices regarding pre-travel information, which attributes both to practical tailored travel advice for Dutch travelers and will also be of interest for future research in the evolving world of travel medicine. Show less
Antimicrobial drugs constitute a fundamental part of modern medicine. The global rise in antimicrobial resistance poses a major threat to global health. Optimising antimicrobial treatment... Show moreAntimicrobial drugs constitute a fundamental part of modern medicine. The global rise in antimicrobial resistance poses a major threat to global health. Optimising antimicrobial treatment strategies in patients offers an important direction to address this challenge. In this thesis, we describe how quantitative characterisation of the drug, the pathogen, and the patients, and how these three factors interact, can help to achieve this goal. To this end, we used a combination of state-of-the-art in silico model-based approaches to analyse and integrate experimental data from in vitro models, and clinical data from healthy volunteers and patients. We developed models describing infection site drug exposure, antimicrobial resistance evolution, and host response biomarker dynamics. We explored the impact of infection on pulmonary pharmacokinetics, evolutionary-based treatment strategies, and the utility host response biomarker for treatment monitoring. The work in this thesis builds towards developing novel strategies to optimise antimicrobial treatments and showcases the importance on interdisciplinary collaborations. Show less
Global healthcare is on the verge of an antibiotic availability crisis as bacteria have evolved resistance to nearly all known antibacterials. Identifying new antibiotics that operate via novel... Show moreGlobal healthcare is on the verge of an antibiotic availability crisis as bacteria have evolved resistance to nearly all known antibacterials. Identifying new antibiotics that operate via novel modes-of-action is therefore of high priority.This thesis contains two drug discovery projects, originating from a antibacterial screen of a compound library. In both projects chemical hits are first structurally optimized, after which their mode-of-action is determined.The first project entails optimizing a hit with potency against MRSA into a submicromolar active antibiotic. By using a chemical proteomics approach, the targets of this compound were elucidated, along with the targets that are most important in its antibacterial activity.The second project concerns Gram-negative bacteria, where a hit molecule is optimized into the conformationally restricted LEI-800. The target of LEI-800 is found to be DNA gyrase, a common antibiotic target. However, it is that LEI-800 inhibits DNA gyrase differently, and more potently, than the status quo. Show less
Court, J.R. de la; Woudt, S.H.S.; Schoffelen, A.F.; Heijmans, J.; Jonge, N.A. de; Bruggen, T. van der; ... ; Schade, R.P. 2022
Objectives Among patients with haematological malignancy, bacteraemia is a common complication during chemotherapy-induced neutropenia. Resistance of gram-negative bacteria (GNB) to third... Show moreObjectives Among patients with haematological malignancy, bacteraemia is a common complication during chemotherapy-induced neutropenia. Resistance of gram-negative bacteria (GNB) to third-generation cephalosporins (3GC) is increasing. In order to explore the value of using surveillance cultures to guide empirical treatment e.g. choosing between carbapenem versus ceftazidime- we aimed to assess the distribution of pathogens causing bacteraemia in patients with haematological malignancy, and the proportion of 3GC-resistant GNB (3GC-R GNB) bacteraemia that was preceded by 3GC-R GNB colonization. Methods Using 11 years of data (2008-2018) from the Dutch national antimicrobial resistance surveillance system, we assessed the prevalence of 3GC-R GNB in episodes of bacteraemia, and the proportion of 3GC-R GNB bacteraemia that was preceded by 3GC-R GNB colonization. Colonization was defined as availability of any GNB surveillance isolate in the year before, independent of the causative micro-organism (time-paired isolates). Results We included 3887 patients, representing 4142 episodes of bacteraemia. GNB were identified in 715/4142 (17.3%), of which 221 (30.9%) were 3GC-R GNB. In 139 of these 221 patients a time-paired surveillance culture was available. In 76.2% (106/139) of patients these surveillance cultures already showed 3GC-R GNB isolates in the year prior to the culture date of the 3GC-R GNB positive blood isolate. Conclusions This multi-centre study shows that in patients with haematological malignancy, the majority of 3GC-R GNB bacteraemia is preceded by 3GC-R GNB colonization. Prospective clinical studies are needed to assess the safety and benefits of the use of surveillance-cultures to guide empirical therapy to restrict the empirical use of carbapenems in this population. Show less
Vancomycin is a last-resort antibiotic for the treatment of many Gram-positive bacterial infections, while remaining inactive against Gram-negative strains. Resistance to vancomycin in Gram... Show moreVancomycin is a last-resort antibiotic for the treatment of many Gram-positive bacterial infections, while remaining inactive against Gram-negative strains. Resistance to vancomycin in Gram-positive stains continues to develop. This thesis describes the recent developments in semisynthetically modifying glycopeptide antibiotics to improve their antibacterial activity. Furthermore, the development of several semisynthetic glycopeptide antibiotics are described including the guanidino lipoglycopeptides, the vancomyxins, and the vancomycin-sideromycins. The guanidino lipoglycopeptides are readily synthesized from vancomycin and display potent in vitro and in vivo activity against Gram-positive bacteria, including vancomycin-resistant strains. Assessment of the activity, properties, and mechanism of action of the guanidino lipoglycopeptides shows the potential of these novel glycopeptides to become best-in class. The vancomyxins, which consist of covalently conjugated vancomycin and outer membrane disruptor polymyxin nonapeptide, display enhanced activity against Gram-negative bacterial strains compared to vancomycin monotherapy or co-administration of the two components. The vancomycin-sideromycins are also aimed at conferring antibacterial activity against Gram-negative bacteria by exploiting an iron-uptake system. Overall, a variety of semisynthetic vancomycin derivatives, aimed at overcoming vancomycin resistance or sensitizing Gram-negative strains, are developed and assessed on their activity in this work. Show less
Background The Dutch Working Party on Antibiotic Policy (SWAB) in collaboration with relevant professional societies, has updated their evidence-based guidelines on empiric antibacterial therapy of... Show moreBackground The Dutch Working Party on Antibiotic Policy (SWAB) in collaboration with relevant professional societies, has updated their evidence-based guidelines on empiric antibacterial therapy of sepsis in adults. Methods Our multidisciplinary guideline committee generated ten population, intervention, comparison, and outcome (PICO) questions relevant for adult patients with sepsis. For each question, a literature search was performed to obtain the best available evidence and assessed using the Grading of Recommendations Assessment, Development, and Evaluation (GRADE) system. The quality of evidence for clinically relevant outcomes was graded from high to very low. In structured consensus meetings, the committee formulated recommendations as strong or weak. When evidence could not be obtained, recommendations were provided based on expert opinion and experience (good practice statements). Results Fifty-five recommendations on the antibacterial therapy of sepsis were generated. Recommendations on empiric antibacterial therapy choices were differentiated for sepsis according to the source of infection, the potential causative pathogen and its resistance pattern. One important revision was the distinction between low, increased and high risk of infection with Enterobacterales resistant to third generation cephalosporins (3GRC-E) to guide the choice of empirical therapy. Other new topics included empirical antibacterial therapy in patients with a reported penicillin allergy and the role of pharmacokinetics and pharmacodynamics to guide dosing in sepsis. We also established recommendations on timing and duration of antibacterial treatment. Conclusions Our multidisciplinary committee formulated evidence-based recommendations for the empiric antibacterial therapy of adults with sepsis in The Netherlands. Show less
Gut colonization with multi-drug resistant organisms (MDROs) or enteropathogenic bacteria such as Clostridioides difficile can precede development of an infection and is considered an important... Show moreGut colonization with multi-drug resistant organisms (MDROs) or enteropathogenic bacteria such as Clostridioides difficile can precede development of an infection and is considered an important public health concern. The gut microbiome is able to confer resistance against colonization and infection of such bacteria and this capability is termed colonization resistance. The aims of this thesis are 1) to recognize and identify bacteria or bacterial communities providing colonization resistance against enteropathogenic microorganisms and antibiotic resistant bacteria, and 2) to contribute to the microbiome research field by developing and applying new technical approaches. This thesis has been divided into three parts. First, current knowledge of microbiome-mediated colonization resistance against enteropathogens is summarized and supplemented with an overview of opportunities and challenges in development of new microbiome-based therapeutics. The second part of this thesis focuses on method optimization for microbiome research, both for wet-lab and dry-lab procedures. The final part describes changes in the human gut microbiota during infection or colonization by potentially pathogenic enteropathogens, including hookworm, C. difficile and MDROs. Show less
A significant proportion of the in-hospital antimicrobial consumption is used in the empiric setting, making empiric therapy an important target of stewardship interventions.Empiric antimicrobial... Show moreA significant proportion of the in-hospital antimicrobial consumption is used in the empiric setting, making empiric therapy an important target of stewardship interventions.Empiric antimicrobial therapy is the antimicrobial regimen that is started when the definite clinical diagnosis, causative agent and/or resistance pattern are yet unknown. Empiric therapy is accompanied by a varying level of uncertainty. In daily clinical practice, this uncertainty about the source, pathogen and susceptibility pattern are often managed by prescribing relatively broad-spectrum antimicrobial therapy. This has potential negative effects, such as toxicity and selective pressure resulting in antimicrobial resistance. Balancing the potential benefits and drawbacks of more broad-spectrum therapy is a substantial challenge, in particular when the level of uncertainty is high.This thesis aims to address the uncertainties most relevant in daily clinical practice in empiric antimicrobial therapy, to determine how they affect daily decision making, and to explore how this can be translated in antimicrobial policy making and antimicrobial stewardship. Show less
Background: During a meticillin-resistant Staphylococcus aureus contact tracing and screening investigation, two borderline oxacillin-resistant Staphylococcus aureus (BORSA)positive screening... Show moreBackground: During a meticillin-resistant Staphylococcus aureus contact tracing and screening investigation, two borderline oxacillin-resistant Staphylococcus aureus (BORSA)positive screening cultures were encountered among neonatal intensive care unit (NICU) healthcare workers (HCWs). This finding led to further investigations. Aim: To assess the likelihood of an outbreak with direct transmission among HCWs. Methods: An infection control team was initiated after the discovery. The team initiated additional infection control measures and evaluated new findings. All NICUs and paediatric ward HCWs were screened for BORSA carriage, and a prospective BORSA seven-week monitoring period for patients was observed. To assess the likelihood of an outbreak with direct transmission among HCWs, the BORSA isolates were analysed using augmented fragment length polymorphism and whole-genome sequencing (WGS). Findings: Positive HCWs were prohibited from clinical work while awaiting the results from the screening programme. In all, 127 NICU and 77 general paediatric ward HCWs were screened for BORSA carriage; five HCWs were BORSA positive. Seventy-two patients were screened during the seven-week period yielding a total of 138 cultures, ranging from one to nine cultures per patient. No spread from HCWs to patients occurred, and the BORSA screening programme was discontinued. WGS analysis with core genome multi-locus sequence typing of all five BORSA strains showed relatedness between two NICU strains. Conclusion: During a seven-week period, no transmission from BORSA-positive HCWs to neonates was observed in either screening or clinical cultures. More vigilance and experience is needed to design adequate evidence-based interventions in the future for this vulnerable population. (c) 2020 Published by Elsevier Ltd on behalf of The Healthcare Infection Society. Show less
Stalenhoef voerde een een gerandomiseerd onderzoek uit op de Spoedeisende Hulp-afdelingen van het LUMC en geaffilieerde ziekenhuizen onder leiding van prof. Jaap van Dissel (Infectieziekten), over... Show moreStalenhoef voerde een een gerandomiseerd onderzoek uit op de Spoedeisende Hulp-afdelingen van het LUMC en geaffilieerde ziekenhuizen onder leiding van prof. Jaap van Dissel (Infectieziekten), over de toepassing van een klinische beslisregel om het risico in te schatten bij patiënten die zich presenteren met pyelonefritis, acute prostatitis of urosepsis.Het onderzoek waaraan 370 patiënten deelnamen, toonde aan dat het aantal ziekenhuisopnames met de toepassing van deze beslisregel significant werd verlaagd. Het aantal thuis behandelde patiënten dat op een later moment toch werd opgenomen, was hierbij hoger dan verwacht. Dit kwam mede doordat er bij een aantal patiënten toch een andere diagnose werd gesteld op het moment dat de kweekuitslagen bekend werden. Verder onderzoek richt zich op verbetering van de beslisregel door deze te combineren met een biomarker die de acute immuunrespons reflecteert. Show less
