H J Nelis

Ghent University, Gand, Flanders, Belgium

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Publications (125)285.26 Total impact


  • No preview · Article · Jun 2015 · Journal of Cystic Fibrosis
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    ABSTRACT: Encapsulation of antibiotics into nanoparticles is a potential strategy to eradicate biofilms. To allow further optimization of nanomedicines for biofilm eradication, the influence of the nanoparticle size on the penetration into dense biofilm clusters needs to be investigated. In the present study, the penetration of nanoparticles with diameters ranging from 40 to 550nm into two biofilms, Burkholderia multivorans LMG 18825 and Pseudomonas aeruginosa LMG 27622, was evaluated using confocal microscopy. Through image analysis, the percentage of particles able to penetrate into dense biofilm clusters was calculated. The size cut off for optimal penetration into biofilm clusters was located around 100 - 130nm for both biofilms. The mesh size of the biofilm matrix and the size of the channels in between the bacteria of the clusters are two factors which likely play a role in the exclusion of the larger particles. For B. multivorans, a sharp drop in the penetration into the clusters is seen for particles larger than 130nm while for P. aeruginosa, a more gradual decrease in penetration could be observed. The overall penetration of the nanoparticles was slightly lower for P. aeruginosa than for B. multivorans. Based on these results, it could be concluded that nanocarriers of about 100nm and smaller are good candidates to improve the treatment of chronic pulmonary biofilms in CF patients. Furthermore, the confocal microscopy method demonstrated here is a useful tool to assess the penetration of nanomedicines in biofilm clusters. Such information is important to optimize nanomedicine formulations for the treatment of biofilm infections.
    No preview · Article · Aug 2014 · Journal of Controlled Release
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    ABSTRACT: Due to the intrinsic resistance of Burkholderia cepacia complex (Bcc) to many antibiotics and the production of a broad range of virulence factors, lung infections by these bacteria, primarily occurring in cystic fibrosis (CF) patients, are very difficult to treat. In addition, the ability of Bcc organisms to form biofilms contributes to their persistence in the CF lung. As Bcc infections are associated with poor clinical outcome, there is an urgent need for new effective therapies to treat these infections. In the present study, we investigated whether liposomal tobramycin displayed an increased anti-biofilm effect against Bcc bacteria compared to free tobramycin. Single particle tracking (SPT) was used to study the transport of positively and negatively charged nanospheres in Bcc biofilms as a model for the transport of liposomes. Negatively charged nanospheres became immobilized in close proximity of biofilm cell clusters, while positively charged nanospheres interacted with fiber-like structures, probably eDNA. Based on these data, encapsulation of tobramycin in negatively charged liposomes appeared promising for targeted drug delivery. However, the anti-biofilm effect of tobramycin encapsulated into neutral or anionic liposomes did not increase compared to that of free tobramycin. Probably, the fusion of the anionic liposomes with the negatively charged bacterial surface of Bcc bacteria was limited by electrostatic repulsive forces. The lack of a substantial anti-biofilm effect of tobramycin encapsulated in neutral liposomes could be further investigated by increasing the liposomal tobramycin concentration. However, this was hampered by the low encapsulation efficiency of tobramycin in these liposomes.
    No preview · Article · Nov 2013 · PLoS ONE
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    Anne-Sophie Messiaen · Hans Nelis · Tom Coenye
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    ABSTRACT: Burkholderia cepacia complex (Bcc) organisms produce a wide variety of potential virulence factors, including exopolysaccharides (EPS), and exhibit intrinsic resistance towards many antibiotics. In the present study we investigated the contribution of Bcc biofilm matrix components, including extracellular DNA, cepacian and poly-β-1,6-N-acetylglucosamine, to tobramycin susceptibility. The in vitro bactericidal activity of tobramycin in combination with recombinant human DNase (rhDNase), NaClO and dispersin B was tested against Bcc biofilms. EPS degradation by NaClO pretreatment and specific PNAG degradation by dispersin B significantly increased the bactericidal effect of tobramycin towards some of the Bcc biofilms tested, including the strains of Burkholderia cenocepacia, B. cepacia and Burkholderia metallica. The presence of rhDNase during biofilm treatment and/or development had no influence on tobramycin activity. These results suggest that EPS play a role in tobramycin susceptibility of Bcc biofilms and that matrix degrading combination therapy could improve treatment of Bcc biofilm infections.
    Full-text · Article · Aug 2013 · Journal of cystic fibrosis: official journal of the European Cystic Fibrosis Society
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    Full-text · Article · Jun 2013 · Journal of Cystic Fibrosis
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    ABSTRACT: Export Date: 22 March 2013, Source: Scopus, Art. No.: e58943
    No preview · Article · Jan 2013 · PLoS ONE
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    ABSTRACT: Aim: The aim of this study was to evaluate the effect of the surface functionalization of model nanoparticles on their mobility in bacterial biofilms and cystic fibrosis sputum. Materials & methods: With single-particle tracking microscopy, the mobility of 0.1- and 0.2-µm fluorescent polyethylene glycol (PEG) modified, carboxylate- and N,N-dimethylethylenediamine-modified polystyrene nanospheres were evaluated in fresh cystic fibrosis sputum, as well as Burkholderia multivorans and Pseudomonas aeruginosa biofilms. Results: PEGylation increased the mobility of the particles in sputum and biofilms, while the charged nanospheres were strongly immobilized. However, the transport of the PEGylated nanoparticles was lower in sputum compared with biofilms. Furthermore, the particle transport showed heterogeneity in samples originating from different patients. Conclusion: This study's data suggest that for future nanocarrier design it will be essential to combine PEGylation with a targeting moiety to ensure sufficient mobility in mucus and a better accumulation of the nanoparticles in the biofilm.
    Full-text · Article · Oct 2012 · Nanomedicine
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    G. Brackman · H.J. Nelis · T. Coenye

    Full-text · Article · Aug 2012
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    ABSTRACT: We investigated the molecular basis of the tolerance of Candida albicans biofilms to antifungals using the miconazole as a model compound, and translated the resulting data to other antifungals. Sessile cells of C. albicans Δefg1, lacking the transcription factor Efg1, showed increased susceptibility to miconazole, amphotericin B and caspofungin, whereas these sessile cells were equally resistant to fluconazole. The increased sensitivity to miconazole was, at least, partly due to an increased accumulation of miconazole in the cells as compared to wild-type or reintegrant Δefg1(EFG1) sessile cells. By using a rat biofilm model, we further confirmed the role of Efg1 in the tolerance of C. albicans biofilms to miconazole when grown in vivo.
    Full-text · Article · Mar 2012 · Journal of Medical Microbiology
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    MA Meire · Tom Coenye · H J Nelis · R J G De Moor
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    ABSTRACT: To compare the antimicrobial efficacy of two-high power lasers (Nd:YAG and Er:YAG) and two commercial antimicrobial photodynamic therapy (aPDT) systems with that of sodium hypochlorite (NaOCl) action on Enterococcus faecalis biofilms grown on dentine discs. Enterococcus faecalis biofilms were grown on dentine discs in a microtiter plate, incubated for 24 h and subjected to the following treatments: aPDT (Denfotex and Helbo system), Er:YAG laser irradiation (2940 nm, 50 mJ or 100 mJ, 15 Hz, 40 s), Nd:YAG laser irradiation (1064 nm, 2 W, 15 Hz, 40 s) and immersion in 2.5% (w/v) NaOCl for 1, 5, 10 and 30 min. Surviving bacteria were harvested, and the number of CFU per disc was determined by plate counting. Significant reductions (anova, P ≤ 0.05) in viable counts were observed for aPDT (Helbo) (2 log(10) reduction), Er:YAG irradiation using 100 mJ pulses (4.3 log(10) reduction) and all NaOCl treatments (>6 log(10) reduction). NaOCl (2.5%) for 5 min effectively eliminated all bacteria. aPDT (Denfotex), Er:YAG irradiation using 50 mJ pulses and Nd:YAG treatment caused a reduction in the viable counts of <1 log(10) unit; these results were not significantly different from the untreated controls. Within the limitations of this particular laboratory set-up, NaOCl was the most effective in E. faecalis biofilm elimination, while Er:YAG laser treatment (100 mJ pulses) also resulted in high reductions in viable counts. The use of both commercial aPDT systems resulted in a weak reduction in the number of E. faecalis cells. Nd:YAG irradiation was the least effective.
    Full-text · Article · Jan 2012 · International Endodontic Journal
  • Tom Coenye · H.J. Nelis

    No preview · Article · Sep 2011 · Journal of Applied Microbiology
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    ABSTRACT: We investigated the cellular mechanisms responsible for the occurrence of miconazole-tolerant persisters in Candida albicans biofilms. Miconazole induced about 30% killing of sessile C. albicans cells at 75 μM. The fraction of miconazole-tolerant persisters, i.e., cells that can survive high doses of miconazole (0.6 to 2.4 mM), in these biofilms was 1 to 2%. Since miconazole induces reactive oxygen species (ROS) in sessile C. albicans cells, we focused on a role for superoxide dismutases (Sods) in persistence and found the expression of Sod-encoding genes in sessile C. albicans cells induced by miconazole compared to the expression levels in untreated sessile C. albicans cells. Moreover, addition of the superoxide dismutase inhibitor N,N′-diethyldithiocarbamate (DDC) to C. albicans biofilms resulted in an 18-fold reduction of the miconazole-tolerant persister fraction and in increased endogenous ROS levels in these cells. Treatment of biofilms of C. albicans clinical isolates with DDC resulted in an 18-fold to more than 200-fold reduction of their miconazole-tolerant persister fraction. To further confirm the important role for Sods in C. albicans biofilm persistence, we used a Δsod4 Δsod5 mutant lacking Sods 4 and 5. Biofilms of the Δsod4 Δsod5 mutant contained at least 3-fold less of the miconazole-tolerant persisters and had increased ROS levels compared to biofilms of the isogenic wild type (WT). In conclusion, the occurrence of miconazole-tolerant persisters in C. albicans biofilms is linked to the ROS-detoxifying activity of Sods. Moreover, Sod inhibitors can be used to potentiate the activity of miconazole against C. albicans biofilms.
    Full-text · Article · Sep 2011 · Antimicrobial Agents and Chemotherapy
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    ABSTRACT: The Burkholderia cepacia complex (BCC) is a group of 17 closely related opportunistic pathogens that are able to infect the respiratory tract of cystic fibrosis patients. BCC bacteria are intrinsically resistant to many antibiotics and are therefore difficult to eradicate. Fosmidomycin could be a new therapeutic agent to treat BCC infections as it inhibits 1-deoxy-d-xylulose-5-phosphate reductoisomerase (Dxr), a key enzyme in the non-mevalonate pathway essential in BCC bacteria for isoprenoid synthesis. In this study, the antimicrobial activity of fosmidomycin and eight fosmidomycin derivatives towards 40 BCC strains was investigated. All BCC strains were resistant to fosmidomycin, although addition of glucose-6-phosphate reduced the minimum inhibitory concentration values of FR900098, the fosmidomycin acetyl derivative, from 512 mg/L to 64 mg/L for Burkholderia multivorans and B. cepacia. This enhanced activity was linked to increased expression of the genes involved in glycerol-3-phosphate transport, which appears to be the only route for fosmidomycin import in BCC bacteria. Furthermore, upregulation of a fosmidomycin resistance gene (fsr) encoding an efflux pump was observed during fosmidomycin and FR900098 treatment. These results strongly suggest that the observed resistance in BCC bacteria is due to insufficient uptake accompanied by fosmidomycin and FR900098 efflux.
    No preview · Article · Jul 2011 · International journal of antimicrobial agents
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    Full-text · Article · Nov 2010 · Journal of Controlled Release
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    ABSTRACT: Ocular bioadhesive minitablets containing gentamicin and vancomycin were developed using different powder mixtures of pregelatinized starch and Carbopol (physical or cospray-dried mixtures). Drug content, antimicrobial activity, and radical formation of the powders used for tablet preparation were evaluated immediately and 30 days after gamma sterilization. Tablet properties and in vitro drug release from the sterilized minitablets were determined. Storage stability of vancomycin and gentamicin in sterilized bioadhesive mixtures was examined by LC-UV/MS and a microbiological assay, respectively. A bioadhesive powder mixture containing only vancomycin was irradiated by X electron-magnetic radiation to evaluate vancomycin stability following sterilization through irradiation. The antimicrobial activity of gentamicin against Staphylococcus epidermidis was not altered in comparison to nonsterilized formulations. Only after an overkill dose of 50 kGy, the concentration of vancomycin decreases to an extent that was pharmaceutically significant. No significant difference in radiation stability between drug substance and product (i.e., powder mixture) was observed. A shift in stability profile was not observed at 6 weeks after irradiation. All other degradation products were present only in small quantities not exceeding 1.0%. The in vitro drug release from the minitablets prepared with physical powder mixtures of pregelatinized starch and Carbopol® 974P NF (96 : 4) was faster compared to the cospray-dried mixtures of starch with Carbopol® 974P NF (ratio: 95:5 and 85:15). The electron paramagnetic resonance signals of the radicals formed during sterilization were still visible after storage for 30 days. The slug mucosal irritation test indicated mild irritation properties of the bioadhesive powder mixtures although no tissue damage was observed.
    No preview · Article · Nov 2010 · Drug Development and Industrial Pharmacy
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    ABSTRACT: Aims: The yeast Saccharomyces boulardii is used as a probiotic for the prevention and treatment of diarrhoea. In this study, the quality of 15 probiotic products containing S. boulardii was verified. Methods and Results: Using microsatellite typing, the identity of all Saccharomyces strains in the products was confirmed as S. boulardii. Additionally, solid-phase cytometry (SPC) and a plate method were used to enumerate S. boulardii cells. SPC was not only able to produce results more rapidly than plating (4 h compared to 48 h) but the cell counts obtained with SPC were significantly higher than the plate counts. Finally, we found that <1% of the S. boulardii cells survived 120 min in gastric conditions and storage for 3 months at 40°C with 75% relative humidity. Conclusions: We developed a SPC method for the quantification of viable S. boulardii cells in probiotics. Additionally, we demonstrated that gastric conditions and storage have a marked effect on the viability of the yeast cells. Significance and Impact of the Study: To our knowledge, this is the first time SPC is used for the quality control of probiotics with S. boulardii. Additionally, we demonstrated the need for gastric protection and accurate storage.
    Full-text · Article · Jun 2010 · Journal of Applied Microbiology
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    ABSTRACT: Candida albicans infections are often associated with biofilm formation. Previous work demonstrated that the expression of HWP1 (hyphal wall protein) and of genes belonging to the ALS (agglutinin-like sequence), SAP (secreted aspartyl protease), PLB (phospholipase B) and LIP (lipase) gene families is associated with biofilm growth on mucosal surfaces. We investigated using real-time PCR whether genes encoding potential virulence factors are also highly expressed in biofilms associated with abiotic surfaces. For this, C. albicans biofilms were grown on silicone in microtiter plates (MTP) or in the Centres for Disease Control (CDC) reactor, on polyurethane in an in vivo subcutaneous catheter rat (SCR) model, and on mucosal surfaces in the reconstituted human epithelium (RHE) model. HWP1 and genes belonging to the ALS, SAP, PLB and LIP gene families were constitutively expressed in C. albicans biofilms. ALS1-5 were upregulated in all model systems, while ALS9 was mostly downregulated. ALS6 and HWP1 were overexpressed in all models except in the RHE and MTP, respectively. The expression levels of SAP1 were more pronounced in both in vitro models, while those of SAP2, SAP4 and SAP6 were higher in the in vivo model. Furthermore, SAP5 was highly upregulated in the in vivo and RHE models. For SAP9 and SAP10 similar gene expression levels were observed in all model systems. PLB genes were not considerably upregulated in biofilms, while LIP1-3, LIP5-7 and LIP9-10 were highly overexpressed in both in vitro models. Furthermore, an elevated lipase activity was detected in supernatans of biofilms grown in the MTP and RHE model. Our findings show that HWP1 and most of the genes belonging to the ALS, SAP and LIP gene families are upregulated in C. albicans biofilms. Comparison of the fold expression between the various model systems revealed similar expression levels for some genes, while for others model-dependent expression levels were observed. This suggests that data obtained in one biofilm model cannot be extrapolated to other model systems. Therefore, the need to use multiple model systems when studying the expression of genes encoding potential virulence factors in C. albicans biofilms is highlighted.
    Full-text · Article · Apr 2010 · BMC Microbiology
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    ABSTRACT: Table S1. Expression levels of ALS genes and HWP1 in biofilms grown in the various model systems.
    Preview · Dataset · Apr 2010
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    ABSTRACT: Table S2. Expression levels of SAP genes in biofilms grown in the various model systems.
    Preview · Dataset · Apr 2010
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    ABSTRACT: Table S3. Expression levels of PLB and LIP genes in biofilms grown in the various model systems.
    Preview · Dataset · Apr 2010

Publication Stats

2k Citations
285.26 Total Impact Points

Institutions

  • 1992-2014
    • Ghent University
      • • Laboratory of Microbiology
      • • Faculty of Pharmaceutical Sciences
      • • Department of Pharmaceutical Analysis
      Gand, Flanders, Belgium
  • 1990
    • Universitair Ziekenhuis Ghent
      Gand, Flanders, Belgium