Louise Dahl Christensen

University of Copenhagen, København, Capital Region, Denmark

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Publications (16)58.44 Total impact

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    ABSTRACT: Injection of soft tissue fillers plays an important role in facial reconstruction and aesthetic treatments such as cosmetic surgery for lip augmentation and wrinkle smoothening. Adverse events are an increasing problem and recently it has been suggested that bacteria are the cause of a vast fraction these. We developed a novel mouse model and evaluated hyaluronic acid gel, calcium hydroxyl apatite microspheres and polyacrylamide hydrogel for their potential for sustaining bacterial infections and their possible treatments. We were able to culture Pseudomonas aeruginosa, Staphylococcus epidermidis and Probionibacterium acnes in all three gels. When contaminated gels were left for 7 days in a mouse model, we found sustainment of bacterial infection with the permanent gel, less with the semi-permanent gel and no growth within the temporary gel. Evaluation of treatment strategies showed that once the bacteria had settled (into biofilms) within the gels, even succesive treatments with high concentrations of relevant antibiotics were not effective. Our data substantiate bacteria as a cause of adverse reactions reported when using tissue fillers, and the sustainability of these infections appears to depend on longevity of the gel. Most importantly, the infections are resistant to antibiotics once established but can be prevented using prophylactic antibiotics This article is protected by copyright. All rights reserved.
    Pathogens and disease. 01/2014;
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    ABSTRACT: Opportunistic pathogenic bacteria can engage in biofilm-based infections that evade immune responses and develop into chronic conditions. Because conventional antimicrobials cannot efficiently eradicate biofilms, there is an urgent need to develop alternative measures to combat biofilm infections. It has recently been established that the secondary messenger c-di-GMP functions as a positive regulator of biofilm formation in several different bacteria. In the present study we investigated if manipulation of the c-di-GMP level in bacteria potentially can be used for biofilm control in vivo. We constructed a Pseudomonas aeruginosa strain in which a reduction in the c-di-GMP level can be achieved via induction of the Escherichia coli YhjH c-di-GMP phosphodiesterase. Initial experiments showed that induction of yhjH expression led to dispersal of the majority of the bacteria in in vitro-grown P. aeruginosa biofilms. Subsequently, we demonstrated that P. aeruginosa biofilms growing on silicone implants, located in the peritoneal cavity of mice, dispersed after induction of the YhjH protein. Bacteria accumulated temporarily in the spleen after induction of biofilm dispersal, but the mice tolerated the dispersed bacteria well. The present work provides proof of the concept that modulation of the c-di-GMP level in bacteria is a viable strategy for biofilm control.
    Infection and immunity 05/2013; · 4.21 Impact Factor
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    ABSTRACT: Chronic infections with Pseudomonas aeruginosa persist because the bacterium forms biofilms that are tolerant to antibiotic treatment and the host immune response. Scanning electron microscopy and confocal laser scanning microscopy were used to visualize biofilm development in vivo following intraperitoneal inoculation of mice with bacteria growing on hollow silicone tubes, as well as to examine the interaction between these bacteria and the host innate immune response. Wild-type P. aeruginosa developed biofilms within 1 day that trapped and caused visible cavities in polymorphonuclear leukocytes (PMNs). In contrast, the number of cells of a P. aeruginosa rhlA mutant that cannot produce rhamnolipids was significantly reduced on the implants by day 1, and the bacteria were actively phagocytosed by infiltrating PMNs. In addition, we identified extracellular wire-like structures around the bacteria and PMNs, which we found to consist of DNA and other polymers. Here we present a novel method to study a pathogen-host interaction in detail. The data presented provide the first direct, high-resolution visualization of the failure of PMNs to protect against bacterial biofilms.
    Infection and immunity 05/2012; 80(8):2601-7. · 4.21 Impact Factor
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    ABSTRACT: In relation to emerging multiresistant bacteria, development of antimicrobials and new treatment strategies of infections should be expected to become a high-priority research area. Quorum sensing (QS), a communication system used by pathogenic bacteria like Pseudomonas aeruginosa to synchronize the expression of specific genes involved in pathogenicity, is a possible drug target. Previous in vitro and in vivo studies revealed a significant inhibition of P. aeruginosa QS by crude garlic extract. By bioassay-guided fractionation of garlic extracts, we determined the primary QS inhibitor present in garlic to be ajoene, a sulfur-containing compound with potential as an antipathogenic drug. By comprehensive in vitro and in vivo studies, the effect of synthetic ajoene toward P. aeruginosa was elucidated. DNA microarray studies of ajoene-treated P. aeruginosa cultures revealed a concentration-dependent attenuation of a few but central QS-controlled virulence factors, including rhamnolipid. Furthermore, ajoene treatment of in vitro biofilms demonstrated a clear synergistic, antimicrobial effect with tobramycin on biofilm killing and a cease in lytic necrosis of polymorphonuclear leukocytes. Furthermore, in a mouse model of pulmonary infection, a significant clearing of infecting P. aeruginosa was detected in ajoene-treated mice compared to a nontreated control group. This study adds to the list of examples demonstrating the potential of QS-interfering compounds in the treatment of bacterial infections.
    Antimicrobial Agents and Chemotherapy 02/2012; 56(5):2314-25. · 4.57 Impact Factor
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    ABSTRACT: Quorum sensing (QS)-deficient Pseudomonas aeruginosa biofilms formed in vitro are more susceptible to tobramycin than QS-proficient P. aeruginosa biofilms, and combination treatment with a QS inhibitor (QSI) and tobramycin shows synergistic effects on the killing of in vitro biofilms. We extended these results to an in vivo P. aeruginosa foreign-body biofilm model. The effect of treatment initiated prophylactically was compared with treatment initiated 11 days post-insertion. Silicone tube implants pre-colonized with wild-type P. aeruginosa were inserted into the peritoneal cavity of BALB/c mice. Mice were treated with intraperitoneal or subcutaneous injections of the QSIs furanone C-30, ajoene or horseradish juice extract in combination with tobramycin. Mice were euthanized on day 1, 2, 3 or 14 post-infection for the estimation of quantitative bacteriology, histopathology and cytokine measurements. Combination treatment of P. aeruginosa resulted in a significantly lower cfu per implant as compared with the placebo groups for all QSIs tested. For early-initiated treatment, a significant difference in clearing was also observed between the combination group and the single-treatment groups, and between the placebo group and the single-treatment groups. In one case a significant difference in clearing was found between the two single-treatment groups. Synergistic antimicrobial efficacy could be achieved when treating mice with both a QSI and tobramycin, resulting in an increased clearance of P. aeruginosa in a foreign-body infection model. Our study highlights the important prospects in developing an early combinatory treatment strategy for chronic infections.
    Journal of Antimicrobial Chemotherapy 02/2012; 67(5):1198-206. · 5.34 Impact Factor
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    ABSTRACT: Foods with health-promoting effects beyond nutritional values have been gaining increasing research focus in recent years, although not much has been published on this subject in relation to bacterial infections. With respect to treatment, a novel antimicrobial strategy, which is expected to transcend problems with selective pressures for antibiotic resistance, is to interrupt bacterial communication, also known as quorum sensing (QS), by means of signal antagonists, the so-called QS inhibitors (QSIs). Furthermore, QSI agents offer a potential solution to the deficiencies associated with use of traditional antibiotics to treat infections caused by bacterial biofilms and multidrug-resistant bacteria. Several QSIs of natural origin have been identified, and in this study, several common food products and plants were extracted and screened for QSI activity in an attempt to isolate and characterize previously unknown QSI compounds active against the common opportunistic pathogen Pseudomonas aeruginosa. Several extracts displayed activity, but horseradish exhibited the highest activity. Chromatographic separation led to the isolation of a potent QSI compound that was identified by liquid chromatography-diode array detector-mass spectrometry (LC-DAD-MS) and nuclear magnetic resonance (NMR) spectroscopy as iberin-an isothiocyanate produced by many members of the Brassicaceae family. Real-time PCR (RT-PCR) and DNA microarray studies showed that iberin specifically blocks expression of QS-regulated genes in P. aeruginosa.
    Applied and Environmental Microbiology 01/2012; 78(7):2410-21. · 3.95 Impact Factor
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    ABSTRACT: In order to study N-acyl homoserine lactone (AHL)-based quorum sensing in vivo, we present a protocol using an Escherichia coli strain equipped with a luxR-based monitor system, which in the presence of exogenous AHL molecules expresses a green fluorescent protein (GFP). Lungs from mice challenged intratracheally with alginate beads containing both a P. aeruginosa strain together with the E. coli monitor strain can be investigated at different time points postinfection. Epifluorescent or confocal scanning laser microscopy (CSLM) is used to detect the GFP-expressing E. coli monitor strain in the lung tissues, indicating production and excretion of AHLs in vivo by the infecting P. aeruginosa.
    Methods in molecular biology (Clifton, N.J.) 01/2011; 692:147-57. · 1.29 Impact Factor
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    ABSTRACT: For a chronic infection to be established, bacteria must be able to cope with hostile conditions such as low iron levels, oxidative stress, and clearance by the host defense, as well as antibiotic treatment. It is generally accepted that biofilm formation facilitates tolerance to these adverse conditions. However, microscopic investigations of samples isolated from sites of chronic infections seem to suggest that some bacteria do not need to be attached to surfaces in order to establish chronic infections. In this study we employed scanning electron microscopy, confocal laser scanning microscopy, RT-PCR as well as traditional culturing techniques to study the properties of Pseudomonas aeruginosa aggregates. We found that non-attached aggregates from stationary-phase cultures have comparable growth rates to surface attached biofilms. The growth rate estimations indicated that, independently of age, both aggregates and flow-cell biofilm had the same slow growth rate as a stationary phase shaking cultures. Internal structures of the aggregates matrix components and their capacity to survive otherwise lethal treatments with antibiotics (referred to as tolerance) and resistance to phagocytes were also found to be strikingly similar to flow-cell biofilms. Our data indicate that the tolerance of both biofilms and non-attached aggregates towards antibiotics is reversible by physical disruption. We provide evidence that the antibiotic tolerance is likely to be dependent on both the physiological states of the aggregates and particular matrix components. Bacterial surface-attachment and subsequent biofilm formation are considered hallmarks of the capacity of microbes to cause persistent infections. We have observed non-attached aggregates in the lungs of cystic fibrosis patients; otitis media; soft tissue fillers and non-healing wounds, and we propose that aggregated cells exhibit enhanced survival in the hostile host environment, compared with non-aggregated bacterial populations.
    PLoS ONE 01/2011; 6(11):e27943. · 3.53 Impact Factor
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    ABSTRACT: The formation of biofilms in conjunction with quorum sensing (QS)-regulated expression of virulence by opportunistic pathogens contributes significantly to immune evasion and tolerance to a variety of antimicrobial treatments. The present protocol describes methods to determine the in vitro efficacy of potential quorum sensing inhibitors (QSIs). Work on Pseudomonas aeruginosa has shown that chemical blockage of QS is a promising new antimicrobial strategy. Several live bacterial reporter systems been developed to screen extracts and pure compounds for QSI activity. Here we describe the usage of reporter strains consisting of a lasB-gfp or rhlA-gfp fusion in P. aeruginosa for qualitative and quantitative evaluation of the inhibition of the two major QS pathways, monitored as reduced expression of green fluorescence. By the use of an in vitro flow cell system it is possible to study the QSI activity by monitoring its ability to interfere with the protective functions of bacterial biofilm. For evaluation of the global effects of QSI compounds, we present a protocol for the DNA microarray-based transcriptomics. Using these in vitro methods it is possible to evaluate the potential of various QSI compounds.
    Methods in molecular biology (Clifton, N.J.) 01/2011; 692:253-63. · 1.29 Impact Factor
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    ABSTRACT: This article will introduce the reader to protocols intended for (i) identification of quorum sensing (QS) inhibitors (QSIs), (ii) characterization of these compounds in vitro and (iii) evaluation of these compounds in animal models. Traditional antimicrobial drugs are designed against planktonic bacteria and not against bacterial biofilms. In biofilms, bacteria are highly resistant to otherwise lethal treatments and they communicate with each other, thus enabling coordinated group behavior. For many years, we have focused on interference with cell to cell communication, also known as QS, with the aim of disabling the expression of virulence and reduction of antibiotic tolerance. Here we present protocols for screening and testing for acyl-homoserine lactone (AHL)-dependent QS inhibition. We also present protocols for the in vivo validation of QSIs as possible drug candidates. The presented methods allow the evaluation of QS inhibition by a potential drug candidate within 2-3 weeks.
    Nature Protocol 01/2010; 5(2):282-93. · 8.36 Impact Factor
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    ABSTRACT: Chronic lung infection with Pseudomonas aeruginosa is the most severe complication for patients with cystic fibrosis (CF). This infection is characterised by endobronchial mucoid biofilms surrounded by numerous polymorphonuclear leucocytes (PMNs). The mucoid phenotype offers protection against the PMNs, which are in general assumed to mount an active respiratory burst leading to lung tissue deterioration. An ongoing respiratory burst by the PMNs has, however, not been demonstrated previously in endobronchial secretions from chronically infected patients with CF. Based on the accumulating evidence for depletion of molecular oxygen (O(2)) in the mucus in infected CF bronchi, it was hypothesised that the O(2) depletion in the mucus in infected CF bronchi may be accelerated by the respiratory burst of the PMNs due to the reduction of O(2) to the superoxide anion (O(-)(2)) by the phagocyte NADPH oxidase (Phox). Methods were established to isolate the O(2) consumption by the respiratory burst from aerobic respiration in freshly expectorated sputum from chronically infected patients with CF. Inhibition of the Phox with diphenylene iodonium (DPI) delayed O(2) depletion, nearly abolished staining of O(-)(2)-producing PMNs with hydroethidine and inhibited the rapid luminol-enhanced chemiluminescence in sputum. Furthermore, the total O(2) consumption was correlated to the concentration of PMNs in the sputum samples. The results demonstrate that CF sputum contains PMNs with an active consumption of O(2) for O(-)(2) production and suggest that the respiratory burst is ongoing and causes accelerated O(2) depletion due to formation of O(-)(2) in the lungs of chronically infected patients with CF.
    Thorax 10/2009; 65(1):57-62. · 8.38 Impact Factor
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    ABSTRACT: Effects of treatment with tobramycin initiated 1 or 24 h post-infection were investigated in a new version of a pulmonary infection model in mice. The model reflects the differentiated behaviour of Pseudomonas aeruginosa mucoid strains isolated from the lungs of one chronically infected cystic fibrosis (CF) patient at different time periods during chronic lung infection. BALB/c mice were challenged with alginate-embedded mucoid clinical isolates isolated in 1988, 1997 or 2003. Mice were euthanized on day 1, 2 or 3 post-infection for estimation of quantitative bacteriology, histopathology, and measurement of granulocyte colony-stimulating factor (G-CSF) and macrophage inflammatory protein 2 (MIP-2). There was a significant reduction of bacteria when comparing treatment initiated 1 h post-infection with treatment initiated after 24 h for isolates 1997 and 2003. Treatment initiated 1 h post-infection also resulted in a reduction of the pulmonary cytokines G-CSF, for all three isolates, and MIP-2, for isolates 1997 and 2003. Histological evaluation showed a shift from the acute-type inflammatory immune response to a chronic-type in mice infected with isolate 2003. A significant reduction in the number of bacteria was observed when initiating treatment 1 h post-infection compared with initiating treatment after 24 h, although the latest isolate avoided complete clearance. Early antibiotic treatment directed at the mucoid phenotype in mice also reduced the inflammation and, thereby, the lung tissue damage.
    Journal of Antimicrobial Chemotherapy 10/2009; 64(6):1241-50. · 5.34 Impact Factor
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    ABSTRACT: Many of the virulence factors produced by the opportunistic human pathogen Pseudomonas aeruginosa are quorum-sensing (QS) regulated. Among these are rhamnolipids, which have been shown to cause lysis of several cellular components of the human immune system, e.g. monocyte-derived macrophages and polymorphonuclear leukocytes (PMNs). We have previously shown that rhamnolipids produced by P. aeruginosa cause necrotic death of PMNs in vitro. This raises the possibility that rhamnolipids may function as a 'biofilm shield'in vivo, which contributes significantly to the increased tolerance of P. aeruginosa biofilms to PMNs. In the present study, we demonstrate the importance of the production of rhamnolipids in the establishment and persistence of P. aeruginosa infections, using an in vitro biofilm system, an intraperitoneal foreign-body model and a pulmonary model of P. aeruginosa infections in mice. Our experimental data showed that a P. aeruginosa strain, unable to produce any detectable rhamnolipids due to an inactivating mutation in the single QS-controlled rhlA gene, did not induce necrosis of PMNs in vitro and exhibited increased clearance compared with its wild-type counterpart in vivo. Conclusively, the results support our model that rhamnolipids are key protective agents of P. aeruginosa against PMNs.
    Apmis 08/2009; 117(7):537-46. · 2.07 Impact Factor
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    ABSTRACT: Polymorphonuclear neutrophilic leukocytes (PMNs) play a central role in innate immunity, where they dominate the response to infections, in particular in the cystic fibrosis lung. PMNs are phagocytic cells that produce a wide range of antimicrobial agents aimed at killing invading bacteria. However, the opportunistic pathogen Pseudomonas aeruginosa can evade destruction by PMNs and thus cause persistent infections. In this study, we show that biofilm cells of P. aeruginosa recognize the presence of attracted PMNs and direct this information to their fellow bacteria through the quorum sensing (QS) signalling system. The bacteria respond to the presence of PMNs by upregulating synthesis of a number of QS-controlled virulence determinants including rhamnolipids, all of which are able to cripple and eliminate cells of the host defence. Our in vitro and in vivo analyses support a 'launch a shield' model by which rhamnolipids surround the biofilm bacteria and on contact eliminate incoming PMNs. Our data strengthen the view that cross-kingdom communication plays a key role in P. aeruginosa recognition and evasion of the host defence.
    Microbiology 08/2009; 155(Pt 11):3500-8. · 3.06 Impact Factor
  • Journal of Cystic Fibrosis - J CYST FIBROS. 01/2008; 7.
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    ABSTRACT: Pseudomonas aeruginosa is an opportunistic human pathogen that causes chronic biofilm-based infections in host organisms. P. aeruginosa employs quorum sensing (QS) to control expression of its virulence, and to establish and maintain chronic infections. Under such conditions, the biofilm mode of growth contributes significantly to P. aeruginosa tolerance to the action of the innate and adaptive defence system and numerous antibiotics. In the present study, an in vivo foreign-body infection model was established in the peritoneal cavity of mice. Experimental data showed that QS-deficient P. aeruginosa are cleared more rapidly from silicone implants as compared to their wild-type counterparts. Concurrently, treatment with the QS inhibitor furanone C-30 of mice harbouring implants colonized with the wild-type P. aeruginosa resulted in a significantly faster clearing of the implants as compared to the placebo-treated group. These results were obtained with both an inbred (BALB/c) and an outbred (NMRI) mouse strain. The present results support a model by which functional QS systems play a pivotal role in the ability of bacteria to resist clearing by the innate immune system and strongly suggest that the efficiency of the mouse innate defence against biofilm-forming P. aeruginosa is improved when the bacteria are treated with QS drugs that induce QS deficiency.
    Microbiology 08/2007; 153(Pt 7):2312-20. · 2.85 Impact Factor

Publication Stats

314 Citations
58.44 Total Impact Points

Institutions

  • 2009–2014
    • University of Copenhagen
      • Department of International Health, Immunology and Microbiology
      København, Capital Region, Denmark
  • 2007–2012
    • Technical University of Denmark
      • Department of Systems Biology
      København, Capital Region, Denmark