Polymyxins are clinically used antibiotics, discovered in mid-20th century. Once abandoned due to excessive nephrotoxicity, they are now used increasingly to address infections caused by multi-drug... Show morePolymyxins are clinically used antibiotics, discovered in mid-20th century. Once abandoned due to excessive nephrotoxicity, they are now used increasingly to address infections caused by multi-drug resistant Gram-negative bacteria.In this thesis, we describe the development and synthesis of analogues of polymyxin, aimed at reducing its associated nephrotoxicity. Analogues were made by semisynthesis, with modifications introduced mostly in the exocyclic portion of the molecule. Especially the introduction of a disulfide bond within the linked lipid helped in reducing the toxicity of the molecules, as evidenced by testing on proximal tubule epithelial cells. For most potent analogues, the antimicrobial activity was completely retained.In addition, this thesis describes studies on the mechanism of action of polymyxin, mostly based on the full stereoisomer of polymyxin B4. This analogue lacks antimicrobial activity, indicating its original stereochemistry to be of utmost importance for its use as an antibiotic.Hybrids based on polymyxin B derivatives are described, addressing non-conventional targets. A hybrid with vancomycin (typically active on Gram-positive bacteria only) shows activity on Gram-negative bacteria. A polymyxin-based hybrid coupled to a peptide with a beta-hairpin motif addresses Gram-negative bacteria, presumably by binding to outer membrane protein BamA. 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
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
Aims: Here we used a mature seven -day biofilm model of Staphylococcus aureus, exposed to antibiotics up to an additional seven days, to establish the effectiveness of either mechanical cleaning or... Show moreAims: Here we used a mature seven -day biofilm model of Staphylococcus aureus, exposed to antibiotics up to an additional seven days, to establish the effectiveness of either mechanical cleaning or antibiotics or non-contact induction heating, and which combinations could eradicate S. aureus in mature biofilms. Methods: Mature biofilms of S. aureus (ATCC 29213) were grown on titanium alloy (Ti6Al4V) coupons for seven days and were subjected to the following treatments or their combinations: antibiotics, mechanical cleaning, or heat shock by induction heating of 60 & DEG;C for one minute. Experiments were repeated at least five times. Results: In the untreated biofilm, growth up to 1.8x1011 colony-forming units (CFU)/cm2 was observed. Treatment with ciprofloxacin, flucloxacillin, vancomycin, cefuroxime, and amoxicillin all with rifampicin gave 6.0 log, 6.1 log, 1.4 log, 4.8 log, and 3.6 log reduction in CFU/cm2, respectively. Mechanical cleaning alone resulted in 4.9 log reduction and induc-tion heating in 7.3 log reduction. There was an additional effect of ciprofloxacin, fluclox-acillin, and induction heating when used in combinations. There was no additional effect for mechanical cleaning. No bacterial growth could be detected after induction heating followed by seven days of ciprofloxacin with rifampicin. Conclusion: Mechanical cleaning, antibiotics, and non-contact induction heating reduced the bacterial load of mature S. aureus biofilms with approximately 5 log or more as a single treatment. The effect of mechanical cleaning on mature S. aureus biofilms was limited when used in combination with antibiotics and/or induction heating. Show less
Background: Although antibiotic treatment is recommended for acute exacerbations of chronic obstructive pulmonary disease (AECOPD), its value in real-world settings is still controversial.... Show moreBackground: Although antibiotic treatment is recommended for acute exacerbations of chronic obstructive pulmonary disease (AECOPD), its value in real-world settings is still controversial. Objectives: This study aimed to evaluate the short- and long-term effects of antibiotic treatment on AECOPD outpatients. Methods: A cohort study was conducted under the PharmLines Initiative. We included participants with a first recorded diagnosis of COPD who received systemic glucocorticoid treatment for an AECOPD episode. The exposed and reference groups were defined based on any antibiotic prescription during the AECOPD treatment. The short-term outcome was AECOPD treatment failure within 14-30 days after the index date. The long-term outcome was time to the next exacerbation. Adjustment for confounding was made using propensity scores. Results: Of the 1,105 AECOPD patients, antibiotics were prescribed to 518 patients (46.9%) while 587 patients (53.1%) received no antibiotics. The overall antibiotic use was associated with a relative risk reduction of AECOPD treatment failure by 37% compared with the reference group (adjusted odds ratio [aOR] 0.63 [95% CI: 0.40-0.99]). Protective effects were similar for doxycycline, macrolides, and co-amoxiclav, although only the effect of doxycycline was statistically significant (aOR 0.53 [95% CI: 0.28-0.99]). No protective effect was seen for amoxicillin (aOR 1.49 [95% CI: 0.78-2.84]). The risk of and time to the next exacerbation was similar for both groups. Conclusion: Overall, antibiotic treatment, notably with doxycycline, supplementing systemic glucocorticoids reduces short-term AECOPD treatment failure in real-world outpatient settings. No long-term beneficial effects of antibiotic treatment on AECOPD were found for the prevention of subsequent exacerbations. Show less
The ongoing increase in antimicrobial resistance combined with the low discovery of novel antibiotics is a serious threat to our health care. Genome mining has given new potential to the field of... Show moreThe ongoing increase in antimicrobial resistance combined with the low discovery of novel antibiotics is a serious threat to our health care. Genome mining has given new potential to the field of natural product discovery, as thousands of biosynthetic gene clusters (BGCs) are discovered for which the natural product is not known.Ribosomally synthesized and post-translationally modified peptides (RiPPs) represent a highly diverse class of natural products. The large number of different modifications that can be applied to a RiPP results in a large variety of chemical structures, but also stems from a large genetic variety in BGCs. As a result, no single method can effectively mine for all RiPP BGCs, making it an interesting source for new molecules.In this thesis, new methods are explored to mine genomes for the BGCs of novel RiPP variants, with a focus on discovering RiPPs that have new modifications. RRE-Finder is a new tool for the detection of RiPP Recognition Elements, domains that are often found in RiPP BGCs. DecRiPPter is another tool that employs machine learning models to discover new RiPP precursor genes encoded in the genomes. Both tools can be used to prioritize novel RiPP BGCs. Two candidate BGCs are characterized, one of which could be shown to specify a new RiPP, validating the approach. Show less
The soil-dwelling, filamentous bacteria of the genus Streptomyces are renowned for their production of useful secondary metabolites including antibiotics. The work described in this thesis provides... Show moreThe soil-dwelling, filamentous bacteria of the genus Streptomyces are renowned for their production of useful secondary metabolites including antibiotics. The work described in this thesis provides new insights on the role and regulation of antibiotic production and resistance in these bacteria. It shows that antibiotic resistance is already beneficial at sub-inhibitory antibiotic concentrations. Resistance can even readily evolve at such low concentrations, thereby possibly explaining the level of resistance seen in pristine environments. Antibiotic producers can benefit from spatial structure, as present in the soil, through the preferential allocation of resources and this enables invasion from low frequencies. Streptomyces do not produce all antibiotics continuously, but antibiotic production is instead tightly regulated in response to environmental cues, including those produced by competitors. Streptomyces are most likely to induce antibiotic production in response to a competitor that shares similar secondary metabolite clusters, indicating a possible role for shared signalling. Besides changes in antibiotic production, other responses to competition are revealed on a transcriptomic level, including an increased expression of developmental genes, suggesting earlier sporulation. Show less
Scope: The Dutch Working Party on Antibiotic Policy constituted a multidisciplinary expert committee to provide evidence-based recommendation for the use of antibacterial therapy in hospitalized... Show moreScope: The Dutch Working Party on Antibiotic Policy constituted a multidisciplinary expert committee to provide evidence-based recommendation for the use of antibacterial therapy in hospitalized adults with a respiratory infection and suspected or proven 2019 Coronavirus disease (COVID-19).Methods: We performed a literature search to answer four key questions. The committee graded the evidence and developed recommendations by using Grading of Recommendations Assessment, Development, and Evaluation methodology.Questions addressed by the guideline and Recommendations: We assessed evidence on the risk of bacterial infections in hospitalized COVID-19 patients, the associated bacterial pathogens, how to diagnose bacterial infections and how to treat bacterial infections. Bacterial co-infection upon admission was reported in 3.5% of COVID-19 patients, while bacterial secondary infections during hospitalization occurred up to 15%. No or very low quality evidence was found to answer the other key clinical questions. Although the evidence base on bacterial infections in COVID-19 is currently limited, available evidence supports restrictive antibiotic use from an antibiotic stewardship perspective, especially upon admission. To support restrictive antibiotic use, maximum efforts should be undertaken to obtain sputum and blood culture samples as well as pneumococcal urinary antigen testing. We suggest to stop antibiotics in patients who started antibiotic treatment upon admission when representative cultures as well as urinary antigen tests show no signs of involvement of bacterial pathogens after 48 hours. For patients with secondary bacterial respiratory infection we recommend to follow other guideline recommendations on antibacterial treatment for patients with hospital-acquired and ventilator-associated pneumonia. An antibiotic treatment duration of five days in patients with COVID-19 and suspected bacterial respiratory infection is recommended upon improvement of signs, symptoms and inflammatory markers. Larger, prospective studies about the epidemiology of bacterial infections in COVID-19 are urgently needed to confirm our conclusions and ultimately prevent unnecessary antibiotic use during the COVID-19 pandemic. (C) 2020 The Author(s). Published by Elsevier Ltd on behalf of European Society of Clinical Microbiology and Infectious Diseases. Show less
Bacterial vaginosis (BV) is perceived as a condition of disrupted vaginal microbiota, but remains of unknown aetiology. In this study, vaginal microbiota composition was determined in twenty-one... Show moreBacterial vaginosis (BV) is perceived as a condition of disrupted vaginal microbiota, but remains of unknown aetiology. In this study, vaginal microbiota composition was determined in twenty-one women with BV, before and after treatment with metronidazole or clindamycin. Microbiota composition varied greatly between women and defining a (un)healthy vaginal microbiota state remains elusive, challenging BV diagnosis and treatment. While relative abundance ofLactobacillusincreased after antibiotic treatment in two-third of women, its abundance was not associated with treatment outcome. Instead, remaining complaints of abnormal vaginal discharge were more common after metronidazole treatment and associated with increased relative abundance ofUreaplasma. Show less
The aim of this thesis was to stimulate rational and effective use of antimicrobials, by addressing the first two cornerstones: (1) refining stewardship of existing antimicrobials and (2) re... Show moreThe aim of this thesis was to stimulate rational and effective use of antimicrobials, by addressing the first two cornerstones: (1) refining stewardship of existing antimicrobials and (2) re-introducing old antibiotics within the framework of antimicrobial stewardship. The overall aim is to contribute to antimicrobial stewardship and to explore the value of the re-introduction of old antibiotics that are currently scarcely used. The basic step is the in vitro relationship expressed as minimal inhibitory concentration (MIC) for a given bacteria for a given antibiotic. The next step is the in vivo situation. This thesis concentrates on the in vivo situation. Show less
Antibiotic resistance is an increasing problem in the battle against (bacterial) infectious diseases. The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) threatens to render... Show moreAntibiotic resistance is an increasing problem in the battle against (bacterial) infectious diseases. The emergence of drug-resistant Mycobacterium tuberculosis (Mtb) threatens to render tuberculosis (TB) untreatable. Efforts to develop novel antibiotics have so far been unsuccessful, calling for additional approaches for treatment of bacterial infections. Intracellular pathogens like Mtb and Salmonella can survive in the host by manipulating host cell signaling. This provides opportunities for novel therapeutic strategies by targeting the host, rather than the bacterium (host-directed therapy). In this thesis we report the development and application of novel (in vitro and in vivo) methods for identifying host genes and proteins involved in host control of intracellular bacteria, as well as chemical compounds that target host molecules as a basis for drug development for host-directed therapies. As a result, we report the identification of RTK inhibitors, the novel kinase inhibitor 97i, the human kinase family PCTAIRE and the host protein DRAM1 as promising leads for further drug development for host-directed therapeutic strategies for intracellular bacterial infections. Show less
Streptomyces are multicellular bacteria that grow as branched filaments and are best known for producing the majority of our antibiotics, many immunosuppressant and anticancer compounds.... Show moreStreptomyces are multicellular bacteria that grow as branched filaments and are best known for producing the majority of our antibiotics, many immunosuppressant and anticancer compounds. Unfortunately their multicellular life style creates many problems for efficient industrial production. In a bioreactor, depending on the environment and the genetics, it can grow quickly as dispersed mycelia or aggregate in slow growing pellets. Either morphology has advantages and disadvantages, which can be product specific. For my thesis I studied the mechanism by which these filaments can aggregate into dense pellets. I found a small gene cluster that produces poly-1,6-N-acetylglucosamine, a bacterial glue which binds neighboring cells and required for pellet formation in S. coelicolor. Subsequently we can use these genes to control the morphology of streptomycetes in a liquid environment, tailoring it for production. My work has given us new insights in the mechanims through which streptomycetes aggregate, but also has the potential to make streptomycetes a more favorable host for industial production. Show less
The explosive increase in infections by pathogens is a major problem in the clinic today. The theme of this thesis was to find novel antibiotics from actinomycetes. Next-generation... Show more The explosive increase in infections by pathogens is a major problem in the clinic today. The theme of this thesis was to find novel antibiotics from actinomycetes. Next-generation sequencing revealed that the biosynthetic potential of actinomycetes had been grossly underestimated. In this thesis, different antibiotics-eliciting strategies, including microbial cocultivation, streptomycin-resistant mutation, overexpression of pathway-specific activator, variation of culture conditions, were utilized to enforce fluctuations in the production of bioactive compounds in actinomycetes, after which, NMR-based metabolic profiling was used to facilitate uncovering those elicited molecules. This pipeline allowed the discovery of new antibiotics involving various chemical skeletons, such as 7-prenylisatin, methoxylated isocoumarins, endophenazines, and C-glycosylpyranonaphthoquinones. On the other hand, genome-mining methodology enabled the discovery of a group of endophenasides and leucanicidin in Kitasatospora sp. MBT66, whereby the rhamnosylation of both scaffold are executed by a same promiscuous glycosyltransferase. Last but not least, a novel antibiotic termed lugdunomycin with unprecedented chemical scaffold, as well as a number of new angucycline-type antibiotics, were characterized from Streptomyces sp. QL37. The biosynthetic pathway of lugdunomycin was deciphered by genetic knockout and OSMAC (One Strain MAny Compound) strategy. In summary, this thesis explores an interface of genomics and metabolomics to accelerate new antibiotics discovery. Show less
