H J Nelis

Ghent University, Gand, Flanders, Belgium

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Publications (204)584.68 Total impact

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    Journal of Cystic Fibrosis 06/2013; 12:S31. · 3.82 Impact Factor
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    ABSTRACT: Export Date: 22 March 2013, Source: Scopus, Art. No.: e58943
    PLoS ONE 01/2013; 8(3). · 3.53 Impact Factor
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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.
    International Endodontic Journal 01/2012; 45(5):482-91. · 2.27 Impact Factor
  • T Coenye, H J Nelis
    Journal of Applied Microbiology 09/2011; 111(5):1296. · 2.39 Impact Factor
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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.
    Drug Development and Industrial Pharmacy 11/2010; 36(11):1259-70. · 2.01 Impact Factor
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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 (4h compared to 48h) 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 120min in gastric conditions and storage for 3months 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.
    Journal of Applied Microbiology 06/2010; 109(5):1745-52. · 2.39 Impact Factor
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    ABSTRACT: As part of studies on the spread of infections, risk factors and prevention, several typing methods were developed to investigate the epidemiology of Aspergillus fumigatus. In the present study, 52 clinical isolates of A. fumigatus from 12 airway specimens from patients with invasive aspergillosis (hospitalized in three different centres) were characterized by short tandem repeat (STR) typing and multilocus sequence typing (MLST). These isolates were previously typed by random amplified polymorphic DNA (RAPD), sequence-specific DNA polymorphism (SSDP), microsatellite polymorphism (MSP) and multilocus enzyme electrophoresis (MLEE). STR typing identified 30 genotypes and, for most patients, all isolates were grouped in one cluster of the unweighted pair group method with arithmetic mean dendrogram. Using MLST, 16 genotypes were identified among 50 isolates, while two isolates appeared untypeable. RAPD, MSP, SSDP and MLEE allowed identification of eight, 14, nine and eight genotypes, respectively. Combining the results of these methods led to the delineation of 25 genotypes and a similar clustering pattern as with STR typing. In general, STR typing led to similar results to the previous combination of RAPD, SSDP, MSP and MLEE, but had a higher resolution, whereas MLST was less discriminatory and resulted in a totally different clustering pattern. Therefore, this study suggests the use of STR typing for research concerning the local epidemiology of A. fumigatus, which requires a high discriminatory power.
    Clinical Microbiology and Infection 07/2009; 15(7):643-50. · 4.58 Impact Factor
  • E. Peeters, H. J. Nelis, T. Coenye
    Journal of Antimicrobial Chemotherapy 03/2009; 63(5):1079-1079. · 5.44 Impact Factor
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    ABSTRACT: To assess the antibacterial action of laser irradiation (Nd:YAG, KTP), photo activated disinfection (PAD) and 2.5% sodium hypochlorite (NaOCl) on Enterococcus faecalis, in an aqueous suspension and in an infected tooth model. Root canals of 60 human teeth with single straight canals were prepared to apical size 50, autoclaved, inoculated with an E. faecalis suspension and incubated for 48 h. They were randomly allocated to four treatment and one control groups. After treatment, the root canals were sampled by flushing with physiological saline, and the number of surviving bacteria in each canal was determined by plate count and solid phase cytometry. The same experimental or control treatments were completed on aqueous suspensions of E. faecalis, and the number of surviving bacteria was determined in the same way. In aqueous suspension, PAD and NaOCl resulted in a significant reduction in the number of E. faecalis cells (P < 0.001), whilst Nd:YAG or KTP had no effect. In the infected tooth model, only the PAD and NaOCl treated teeth yielded significantly different results relative to the untreated controls (P < 0.001). The laser systems as well as PAD were less effective than NaOCl in reducing E. faecalis, both in aqueous suspension and in the infected tooth model.
    International Endodontic Journal 02/2009; 42(4):351-9. · 2.27 Impact Factor
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    K De Prijck, E Peeters, H J Nelis
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    ABSTRACT: To compare the survival of four bacterial strains (Escherichia coli, Proteus mirabilis, Staphylococcus aureus, Pseudomonas aeruginosa) in pharmaceutical oils, including jojoba oil/tea tree oil, carbol oil, jojoba oil and sesame oil. Oils were spiked with the test bacteria in a concentration of 10(4) CFU ml(-1). Bacteria were extracted from oils with phosphate-buffered saline containing 0.5% Tween 20. Aliquots of the pooled water layers were analysed by solid-phase cytometry and plate counting. Plate counts dropped to zero for all test strains exposed for 24 h to three of the four oils. In contrast, significant numbers of viable cells were still detected by SPC, except in the jojoba oil/tea tree oil mixture and partly in sesame oil. Exposure of bacteria for 24 h to the two oils containing an antimicrobial led to a loss of their culturability but not necessarily of their viability. The antibacterial activity of the jojoba oil/tea tree oil mixture supersedes that of carbol oil. These in vitro data suggest that the jojoba oil/tea tree oil mixture more than carbol oil inhibits bacterial proliferation when used for intermittent self-catherization.
    Letters in Applied Microbiology 01/2009; 47(6):571-3. · 1.63 Impact Factor
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    Acta Clinica Croatica; Vol.48 No.1. 01/2009;
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    ABSTRACT: To evaluate the susceptibility to microbial contamination that occurs during simulated handling of protective devices for the preparation of cytotoxic drug solutions. Four devices, i.e. Chemoprotect spike, Clave connector, PhaSeal and Securmix were challenged with low and high inocula of micro-organisms. The cells, transferred to the connected vials during repeated manipulations of the devices were counted by means of solid-phase cytometry. Of the four devices, PhaSeal afforded the lowest transfer of micro-organisms. Secondly, the efficiency of procedures for the disinfection of an artificially contaminated rubber stopper was compared prior to connection of the vial to the PhaSeal device. Spraying or swabbing alone was inadequate, as opposed to a combination of spraying [0.5% or 2.0% (w/v) chlorhexidine in isopropanol] and swabbing [70% (v/v) isopropanol]. Although Phaseal afforded the lowest transfer of micro-organisms, adequate disinfection of the vial prior to connection remains required. Unlike aspects of operator protection, which are well documented, the microbiological safety of protective devices for the preparation of cytotoxic drugs has not been addressed in the literature. This study estimates the susceptibility to microbial contamination during handling of four commonly used devices.
    Letters in Applied Microbiology 01/2009; 47(6):543-8. · 1.63 Impact Factor
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    E Peeters, H J Nelis, T Coenye
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    ABSTRACT: In the present study we evaluated the efficacy of various procedures recommended for the disinfection of respiratory equipment and other materials in cystic fibrosis, using both planktonic and sessile Burkholderia cenocepacia cells. A modified European Suspension Test was performed to determine the effects of the disinfection procedures on planktonic cells. The ability of the treatments to kill sessile cells and to remove biofilm biomass was evaluated using two resazurin-based viability assays and a crystal violet staining on biofilms grown and treated in 96-well microtitre plates. The effect of chlorhexidine and hydrogen peroxide treatments on the viability of sessile B. cenocepacia cells was clearly reduced compared to the effects on planktonic cells. Treatments with low concentrations of sodium hypochlorite (0.05%, 5 min) and acetic acid (1.25%, 15 min) also resulted in insufficient reductions in the number of viable sessile cells. There was no relation between the ability of the disinfectants to remove biofilm biomass and their potential to kill biofilm cells. In conclusion, our study indicates that testing of the efficacy of disinfectants should be performed on both planktonic and sessile cells, with particular attention to their effects on cellular viability.
    Journal of Hospital Infection 01/2009; 70(4):361-8. · 2.78 Impact Factor
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    T Coenye, K Honraet, B Rossel, H J Nelis
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    ABSTRACT: It is generally accepted that many human infections are biofilm-related and that sessile (biofilm-grown) cells are highly resistant against antimicrobial agents. Propionibacterium acnes plays a role in the pathogenesis of acne vulgaris, a common disorder of the pilosebaceous follicles and it has been suggested that P. acnes cells residing within the follicles grow as a biofilm. Although P. acnes biofilms have not been observed directly in the pilosebaceous unit, the observation that P. acnes readily forms biofilm in vitro as well as on various medical devices in vivo, combined with the high resistance of sessile P. acnes cells and the increased production of particular virulence factors and qourum sensing molecules in sessile cells point in this direction. In addition, in vitro and in vivo biofilm formation has also been demonstrated for other microorganisms involved in skin diseases (including Staphylococcus aureus and Streptococcus pyogenes).
    Infectious Disorders - Drug Targets(Formerly Current Drug Targets - Infectious Disorders) 10/2008; 8(3):156-9.
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    ABSTRACT: The intracellular behaviour of a Flavobacterium psychrophilum strain, ingested by spleen phagocytes of rainbow trout, Oncorhynchus mykiss, of different ages, was assessed in vivo. Three groups of rainbow trout weighing 1 g (aged 10 weeks), 25 g (aged 20 weeks) and 300 g (aged 15 months), respectively, were injected intraperitoneally with 1 × 106 cfu of a F. psychrophilum strain. It was found that only fry, aged 10 weeks, displayed clinical signs and suffered mortality. Bacteriological colony plating of different organs demonstrated that the spleen and to a lesser extent the kidney of only the fry were affected. The number of colony forming units per gram of spleen tissue increased with time. No bacteria were found in the trout aged 5 months and older. Light microscopical examination and epifluorescence microscopy revealed that the fry spleen phagocytes contained an increasing number of viable intracellular F. psychrophilum bacteria over time. Again, no bacteria were encountered in the phagocytes collected from older fish.
    Journal of Fish Diseases 07/2008; 24(8):481 - 487. · 1.51 Impact Factor
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    ABSTRACT: The trailing endpoint phenotype observed during testing of Candida albicans susceptibility to azoles according to the CLSI procedure is defined as a difference in MIC depending on whether the result is obtained after 24 or 48 h. This study investigated whether intrinsic differences between the EUCAST and CLSI methods could explain trailing growth. The glucose concentration in the medium and the shape of the microtitre plate wells were both found to be involved. In order to reduce the incidence of trailing growth according to the CLSI procedure, the use of higher glucose concentrations and flat-bottomed microtitre plates could be valuable improvements.
    Clinical Microbiology and Infection 06/2008; 14(5):495-7. · 5.20 Impact Factor
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    ABSTRACT: A series of 256 Aspergillus fumigatus isolates, recovered from eight patients with cystic fibrosis (CF), were genotyped using microsatellite-based typing. Only a limited number of genotypes were shared between patients and co-colonisation with multiple strains was indicated for all patients. Additionally, some genotypes were isolated recurrently, indicating that they are capable of prolonged colonisation.
    European Journal of Clinical Microbiology 06/2008; 27(10):1005-7. · 3.02 Impact Factor
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    ABSTRACT: To evaluate the use of the modified Robbins device (MRD) to test disinfection strategies against biofilms that form on oral medical devices and to test the biofilm removal efficacy of NitrAdine, a disinfectant for the maintenance of oral medical devices. Biofilms were grown on discs using the MRD and biofilms formed in this system were used to evaluate the efficacy of NitrAdine and to determine the optimal disinfection conditions. Our data indicate that the use of the MRD allows for the rapid and reproducible formation of high-density biofilms. Determination of the efficacy of NitrAdine revealed high activity against biofilms tested (e.g. >3 log reduction for Candida albicans and Staphylococcus aureus) and allowed the determination of the optimal conditions for its use. The high reproducibility and flexibility of the MRD make it an excellent candidate for standardized testing of disinfectants aimed at reducing biofilms on oral medical devices. Using this system, we were able to demonstrate that NitrAdine exhibits high activity against biofilms formed by the micro-organisms tested. Our data suggest that our procedure is appropriate for standardized testing of disinfectants aimed at reducing biofilms on oral medical devices.
    Journal of Applied Microbiology 03/2008; 105(3):733-40. · 2.39 Impact Factor
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    ABSTRACT: The in vivo behaviour of 5% gentamicin sulphate ocular mini-tablets (2-mm diameter, 6.525 mg weight) was compared with gentamicin eye drops in six ponies. Two mini-tablets were inserted on the bulbar conjunctiva of the right eye while a similar dose of gentamicin was administered via eye drops in the left eye. Irritation induced by the mini-tablets and the eye drops was evaluated using a visual analogue scale (0-10). Tears were sampled with ophthalmologic absorption triangles for 1 min for the determination of the concentration of gentamicin sulphate using a microbiological plate diffusion method. Irritation induced by the tablets was minor and clinically acceptable (overall median score of 1.7 +/- 1.4). Eye drops induced a sharp increase in gentamicin sulphate concentration (364.4 microg/mL after 5 min) followed by a fast decline (10.8 microg/mL after 60 min). The increase in concentration induced by the ocular mini-tablets was less pronounced (up to 56.2 microg/mL after 30 min) and followed by a gradual decrease; the concentration remained above 15 microg/mL for 8 h. Ocular 5% gentamicin sulphate mini-tablets are clinically well-tolerated in ponies, assuring a constant concentration in the tears for at least 8 h.
    Journal of Veterinary Pharmacology and Therapeutics 11/2007; 30(5):470-6. · 1.32 Impact Factor
  • Planta Medica 01/2007; 73(9):920-920. · 2.35 Impact Factor

Publication Stats

3k Citations
584.68 Total Impact Points

Institutions

  • 1994–2012
    • Ghent University
      • • Laboratory of Microbiology
      • • Faculty of Pharmaceutical Sciences
      • • Department of Pharmaceutical Analysis
      Gand, Flanders, Belgium
  • 1988–1990
    • Universitair Ziekenhuis Ghent
      Gand, Flanders, Belgium