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The Staphylococcus aureus response to unsaturated long chain free fatty acids: survival mechanisms and virulence implications.
PUBLISHED: 02-02-2009
Staphylococcus aureus is an important human commensal and opportunistic pathogen responsible for a wide range of infections. Long chain unsaturated free fatty acids represent a barrier to colonisation and infection by S. aureus and act as an antimicrobial component of the innate immune system where they are found on epithelial surfaces and in abscesses. Despite many contradictory reports, the precise anti-staphylococcal mode of action of free fatty acids remains undetermined. In this study, transcriptional (microarrays and qRT-PCR) and translational (proteomics) analyses were applied to ascertain the response of S. aureus to a range of free fatty acids. An increase in expression of the sigma(B) and CtsR stress response regulons was observed. This included increased expression of genes associated with staphyloxanthin synthesis, which has been linked to membrane stabilisation. Similarly, up-regulation of genes involved in capsule formation was recorded as were significant changes in the expression of genes associated with peptidoglycan synthesis and regulation. Overall, alterations were recorded predominantly in pathways involved in cellular energetics. In addition, sensitivity to linoleic acid of a range of defined (sigB, arcA, sasF, sarA, agr, crtM) and transposon-derived mutants (vraE, SAR2632) was determined. Taken together, these data indicate a common mode of action for long chain unsaturated fatty acids that involves disruption of the cell membrane, leading to interference with energy production within the bacterial cell. Contrary to data reported for other strains, the clinically important EMRSA-16 strain MRSA252 used in this study showed an increase in expression of the important virulence regulator RNAIII following all of the treatment conditions tested. An adaptive response by S. aureus of reducing cell surface hydrophobicity was also observed. Two fatty acid sensitive mutants created during this study were also shown to diplay altered pathogenesis as assessed by a murine arthritis model. Differences in the prevalence and clinical importance of S. aureus strains might partly be explained by their responses to antimicrobial fatty acids.
Authors: Marshall L. Deline, Tracy L. Vrablik, Jennifer L. Watts.
Published: 11-29-2013
Fatty acids are essential for numerous cellular functions. They serve as efficient energy storage molecules, make up the hydrophobic core of membranes, and participate in various signaling pathways. Caenorhabditis elegans synthesizes all of the enzymes necessary to produce a range of omega-6 and omega-3 fatty acids. This, combined with the simple anatomy and range of available genetic tools, make it an attractive model to study fatty acid function. In order to investigate the genetic pathways that mediate the physiological effects of dietary fatty acids, we have developed a method to supplement the C. elegans diet with unsaturated fatty acids. Supplementation is an effective means to alter the fatty acid composition of worms and can also be used to rescue defects in fatty acid-deficient mutants. Our method uses nematode growth medium agar (NGM) supplemented with fatty acidsodium salts. The fatty acids in the supplemented plates become incorporated into the membranes of the bacterial food source, which is then taken up by the C. elegans that feed on the supplemented bacteria. We also describe a gas chromatography protocol to monitor the changes in fatty acid composition that occur in supplemented worms. This is an efficient way to supplement the diets of both large and small populations of C. elegans, allowing for a range of applications for this method.
19 Related JoVE Articles!
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Analysis of Fatty Acid Content and Composition in Microalgae
Authors: Guido Breuer, Wendy A. C. Evers, Jeroen H. de Vree, Dorinde M. M. Kleinegris, Dirk E. Martens, René H. Wijffels, Packo P. Lamers.
Institutions: Wageningen University and Research Center, Wageningen University and Research Center, Wageningen University and Research Center.
A method to determine the content and composition of total fatty acids present in microalgae is described. Fatty acids are a major constituent of microalgal biomass. These fatty acids can be present in different acyl-lipid classes. Especially the fatty acids present in triacylglycerol (TAG) are of commercial interest, because they can be used for production of transportation fuels, bulk chemicals, nutraceuticals (ω-3 fatty acids), and food commodities. To develop commercial applications, reliable analytical methods for quantification of fatty acid content and composition are needed. Microalgae are single cells surrounded by a rigid cell wall. A fatty acid analysis method should provide sufficient cell disruption to liberate all acyl lipids and the extraction procedure used should be able to extract all acyl lipid classes. With the method presented here all fatty acids present in microalgae can be accurately and reproducibly identified and quantified using small amounts of sample (5 mg) independent of their chain length, degree of unsaturation, or the lipid class they are part of. This method does not provide information about the relative abundance of different lipid classes, but can be extended to separate lipid classes from each other. The method is based on a sequence of mechanical cell disruption, solvent based lipid extraction, transesterification of fatty acids to fatty acid methyl esters (FAMEs), and quantification and identification of FAMEs using gas chromatography (GC-FID). A TAG internal standard (tripentadecanoin) is added prior to the analytical procedure to correct for losses during extraction and incomplete transesterification.
Environmental Sciences, Issue 80, chemical analysis techniques, Microalgae, fatty acid, triacylglycerol, lipid, gas chromatography, cell disruption
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Biochemical and High Throughput Microscopic Assessment of Fat Mass in Caenorhabditis Elegans
Authors: Elizabeth C. Pino, Christopher M. Webster, Christopher E. Carr, Alexander A. Soukas.
Institutions: Massachusetts General Hospital and Harvard Medical School, Massachusetts Institute of Technology.
The nematode C. elegans has emerged as an important model for the study of conserved genetic pathways regulating fat metabolism as it relates to human obesity and its associated pathologies. Several previous methodologies developed for the visualization of C. elegans triglyceride-rich fat stores have proven to be erroneous, highlighting cellular compartments other than lipid droplets. Other methods require specialized equipment, are time-consuming, or yield inconsistent results. We introduce a rapid, reproducible, fixative-based Nile red staining method for the accurate and rapid detection of neutral lipid droplets in C. elegans. A short fixation step in 40% isopropanol makes animals completely permeable to Nile red, which is then used to stain animals. Spectral properties of this lipophilic dye allow it to strongly and selectively fluoresce in the yellow-green spectrum only when in a lipid-rich environment, but not in more polar environments. Thus, lipid droplets can be visualized on a fluorescent microscope equipped with simple GFP imaging capability after only a brief Nile red staining step in isopropanol. The speed, affordability, and reproducibility of this protocol make it ideally suited for high throughput screens. We also demonstrate a paired method for the biochemical determination of triglycerides and phospholipids using gas chromatography mass-spectrometry. This more rigorous protocol should be used as confirmation of results obtained from the Nile red microscopic lipid determination. We anticipate that these techniques will become new standards in the field of C. elegans metabolic research.
Genetics, Issue 73, Biochemistry, Cellular Biology, Molecular Biology, Developmental Biology, Physiology, Anatomy, Caenorhabditis elegans, Obesity, Energy Metabolism, Lipid Metabolism, C. elegans, fluorescent lipid staining, lipids, Nile red, fat, high throughput screening, obesity, gas chromatography, mass spectrometry, GC/MS, animal model
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Subcutaneous Infection of Methicillin Resistant Staphylococcus Aureus (MRSA)
Authors: Ching Wen Tseng, Marisel Sanchez-Martinez, Andrea Arruda, George Y. Liu.
Institutions: Cedars-Sinai Medical Center.
MRSA is a worldwide threat to public health, and MRSA skin and soft-tissue infections now account for more than half of all soft-tissue infections in the United States. Among soft-tissue infections, myositis, pyomyositis, and necrotizing fasciitis have been increasingly reported in association with MRSA arising from the community. To understand the interplay between MRSA and host immunity leading to more severe infection, the availability of animal models is critical, permitting the study of host and bacterial factors. Several infection models have been introduced to assess the pathogenesis of S. aureus during superficial skin infection. Here, we describe a subcutaneous infection model that examines the skin, subcutaneous, and muscle pathologies.
Infection, Issue 48, Subcutaneous infection, Staphylococcus aureus, MRSA
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Microtiter Dish Biofilm Formation Assay
Authors: George A. O'Toole.
Institutions: Dartmouth Medical School.
Biofilms are communities of microbes attached to surfaces, which can be found in medical, industrial and natural settings. In fact, life in a biofilm probably represents the predominate mode of growth for microbes in most environments. Mature biofilms have a few distinct characteristics. Biofilm microbes are typically surrounded by an extracellular matrix that provides structure and protection to the community. Microbes growing in a biofilm also have a characteristic architecture generally comprised of macrocolonies (containing thousands of cells) surrounded by fluid-filled channels. Biofilm-grown microbes are also notorious for their resistance to a range of antimicrobial agents including clinically relevant antibiotics. The microtiter dish assay is an important tool for the study of the early stages in biofilm formation, and has been applied primarily for the study of bacterial biofilms, although this assay has also been used to study fungal biofilm formation. Because this assay uses static, batch-growth conditions, it does not allow for the formation of the mature biofilms typically associated with flow cell systems. However, the assay has been effective at identifying many factors required for initiation of biofilm formation (i.e, flagella, pili, adhesins, enzymes involved in cyclic-di-GMP binding and metabolism) and well as genes involved in extracellular polysaccharide production. Furthermore, published work indicates that biofilms grown in microtiter dishes do develop some properties of mature biofilms, such a antibiotic tolerance and resistance to immune system effectors. This simple microtiter dish assay allows for the formation of a biofilm on the wall and/or bottom of a microtiter dish. The high throughput nature of the assay makes it useful for genetic screens, as well as testing biofilm formation by multiple strains under various growth conditions. Variants of this assay have been used to assess early biofilm formation for a wide variety of microbes, including but not limited to, pseudomonads, Vibrio cholerae, Escherichia coli, staphylocci, enterococci, mycobacteria and fungi. In the protocol described here, we will focus on the use of this assay to study biofilm formation by the model organism Pseudomonas aeruginosa. In this assay, the extent of biofilm formation is measured using the dye crystal violet (CV). However, a number of other colorimetric and metabolic stains have been reported for the quantification of biofilm formation using the microtiter plate assay. The ease, low cost and flexibility of the microtiter plate assay has made it a critical tool for the study of biofilms.
Immunology, Issue 47, Biofilm, assay, bacteria, fungi, microtiter, static
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Experimental Endocarditis Model of Methicillin Resistant Staphylococcus aureus (MRSA) in Rat
Authors: Wessam Abdel Hady, Arnold S. Bayer, Yan Q. Xiong.
Institutions: Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Geffen School of Medicine at UCLA.
Endovascular infections, including endocarditis, are life-threatening infectious syndromes1-3. Staphylococcus aureus is the most common world-wide cause of such syndromes with unacceptably high morbidity and mortality even with appropriate antimicrobial agent treatments4-6. The increase in infections due to methicillin-resistant S. aureus (MRSA), the high rates of vancomycin clinical treatment failures and growing problems of linezolid and daptomycin resistance have all further complicated the management of patients with such infections, and led to high healthcare costs7, 8. In addition, it should be emphasized that most recent studies with antibiotic treatment outcomes have been based in clinical settings, and thus might well be influenced by host factors varying from patient-to-patient. Therefore, a relevant animal model of endovascular infection in which host factors are similar from animal-to-animal is more crucial to investigate microbial pathogenesis, as well as the efficacy of novel antimicrobial agents. Endocarditis in rat is a well-established experimental animal model that closely approximates human native valve endocarditis. This model has been used to examine the role of particular staphylococcal virulence factors and the efficacy of antibiotic treatment regimens for staphylococcal endocarditis. In this report, we describe the experimental endocarditis model due to MRSA that could be used to investigate bacterial pathogenesis and response to antibiotic treatment.
Infection, Issue 64, Immunology, Staphylococcus aureus, endocarditis, animal model, methicillin resistance, MRSA, rat
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One-day Workflow Scheme for Bacterial Pathogen Detection and Antimicrobial Resistance Testing from Blood Cultures
Authors: Wendy L.J. Hansen, Judith Beuving, Annelies Verbon, Petra. F.G. Wolffs.
Institutions: Maastricht University Medical Center, Erasmus Medical Center.
Bloodstream infections are associated with high mortality rates because of the probable manifestation of sepsis, severe sepsis and septic shock1. Therefore, rapid administration of adequate antibiotic therapy is of foremost importance in the treatment of bloodstream infections. The critical element in this process is timing, heavily dependent on the results of bacterial identification and antibiotic susceptibility testing. Both of these parameters are routinely obtained by culture-based testing, which is time-consuming and takes on average 24-48 hours2, 4. The aim of the study was to develop DNA-based assays for rapid identification of bloodstream infections, as well as rapid antimicrobial susceptibility testing. The first assay is a eubacterial 16S rDNA-based real-time PCR assay complemented with species- or genus-specific probes5. Using these probes, Gram-negative bacteria including Pseudomonas spp., Pseudomonas aeruginosa and Escherichia coli as well as Gram-positive bacteria including Staphylococcus spp., Staphylococcus aureus, Enterococcus spp., Streptococcus spp., and Streptococcus pneumoniae could be distinguished. Using this multiprobe assay, a first identification of the causative micro-organism was given after 2 h. Secondly, we developed a semi-molecular assay for antibiotic susceptibility testing of S. aureus, Enterococcus spp. and (facultative) aerobe Gram-negative rods6. This assay was based on a study in which PCR was used to measure the growth of bacteria7. Bacteria harvested directly from blood cultures are incubated for 6 h with a selection of antibiotics, and following a Sybr Green-based real-time PCR assay determines inhibition of growth. The combination of these two methods could direct the choice of a suitable antibiotic therapy on the same day (Figure 1). In conclusion, molecular analysis of both identification and antibiotic susceptibility offers a faster alternative for pathogen detection and could improve the diagnosis of bloodstream infections.
Immunology, Issue 65, Infection, Medicine, Microbiology, Bacteria, real-time PCR, probes, pathogen detection, blood culture, 16S rDNA gene, antibiotic resistance, antibiotic susceptibility testing
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Invasion of Human Cells by a Bacterial Pathogen
Authors: Andrew M. Edwards, Ruth C. Massey.
Institutions: University of Bath.
Here we will describe how we study the invasion of human endothelial cells by bacterial pathogen Staphylococcus aureus . The general protocol can be applied to the study of cell invasion by virtually any culturable bacterium. The stages at which specific aspects of invasion can be studied, such as the role of actin rearrangement or caveolae, will be highlighted. Host cells are grown in flasks and when ready for use are seeded into 24-well plates containing Thermanox coverslips. Using coverslips allows subsequent removal of the cells from the wells to reduce interference from serum proteins deposited onto the sides of the wells (to which S. aureus would attach). Bacteria are grown to the required density and washed to remove any secreted proteins (e.g. toxins). Coverslips with confluent layers of endothelial cells are transferred to new 24-well plates containing fresh culture medium before the addition of bacteria. Bacteria and cells are then incubated together for the required amount of time in 5% CO2 at 37°C. For S. aureus this is typically between 15-90 minutes. Thermanox coverslips are removed from each well and dip-washed in PBS to remove unattached bacteria. If total associated bacteria (adherent and internalised) are to be quantified, coverslips are then placed in a fresh well containing 0.5% Triton X-100 in PBS. Gentle pipetting leads to complete cell lysis and bacteria are enumerated by serial dilution and plating onto agar. If the number of bacteria that have invaded the cells is needed, coverslips are added to wells containing 500 μl tissue culture medium supplemented with gentamicin and incubation continued for 1 h, which will kill all external bacteria. Coverslips can then be washed, cells lysed and bacteria enumerated by plating onto agar as described above. If the experiment requires direct visualisation, coverslips can be fixed and stained for light, fluorescence or confocal microscopy or prepared for electron microscopy.
Infection, Issue 49, Bacterial pathogen, host cell invasion, Staphylococcus aureus, invasin
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Staphylococcus aureus Growth using Human Hemoglobin as an Iron Source
Authors: Gleb Pishchany, Kathryn P. Haley, Eric P. Skaar.
Institutions: Vanderbilt University Medical School.
S. aureus is a pathogenic bacterium that requires iron to carry out vital metabolic functions and cause disease. The most abundant reservoir of iron inside the human host is heme, which is the cofactor of hemoglobin. To acquire iron from hemoglobin, S. aureus utilizes an elaborate system known as the iron-regulated surface determinant (Isd) system1. Components of the Isd system first bind host hemoglobin, then extract and import heme, and finally liberate iron from heme in the bacterial cytoplasm2,3. This pathway has been dissected through numerous in vitro studies4-9. Further, the contribution of the Isd system to infection has been repeatedly demonstrated in mouse models8,10-14. Establishing the contribution of the Isd system to hemoglobin-derived iron acquisition and growth has proven to be more challenging. Growth assays using hemoglobin as a sole iron source are complicated by the instability of commercially available hemoglobin, contaminating free iron in the growth medium, and toxicity associated with iron chelators. Here we present a method that overcomes these limitations. High quality hemoglobin is prepared from fresh blood and is stored in liquid nitrogen. Purified hemoglobin is supplemented into iron-deplete medium mimicking the iron-poor environment encountered by pathogens inside the vertebrate host. By starving S. aureus of free iron and supplementing with a minimally manipulated form of hemoglobin we induce growth in a manner that is entirely dependent on the ability to bind hemoglobin, extract heme, pass heme through the bacterial cell envelope and degrade heme in the cytoplasm. This assay will be useful for researchers seeking to elucidate the mechanisms of hemoglobin-/heme-derived iron acquisition in S. aureus and possibly other bacterial pathogens.
Infection, Issue 72, Immunology, Microbiology, Infectious Diseases, Cellular Biology, Pathology, Micronutrients, Bacterial Infections, Gram-Positive Bacterial Infections, Bacteriology, Staphylococcus aureus, iron acquisition, hemoglobin, bacterial growth, bacteria
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Isolation and Chemical Characterization of Lipid A from Gram-negative Bacteria
Authors: Jeremy C. Henderson, John P. O'Brien, Jennifer S. Brodbelt, M. Stephen Trent.
Institutions: The University of Texas at Austin, The University of Texas at Austin, The University of Texas at Austin.
Lipopolysaccharide (LPS) is the major cell surface molecule of gram-negative bacteria, deposited on the outer leaflet of the outer membrane bilayer. LPS can be subdivided into three domains: the distal O-polysaccharide, a core oligosaccharide, and the lipid A domain consisting of a lipid A molecular species and 3-deoxy-D-manno-oct-2-ulosonic acid residues (Kdo). The lipid A domain is the only component essential for bacterial cell survival. Following its synthesis, lipid A is chemically modified in response to environmental stresses such as pH or temperature, to promote resistance to antibiotic compounds, and to evade recognition by mediators of the host innate immune response. The following protocol details the small- and large-scale isolation of lipid A from gram-negative bacteria. Isolated material is then chemically characterized by thin layer chromatography (TLC) or mass-spectrometry (MS). In addition to matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) MS, we also describe tandem MS protocols for analyzing lipid A molecular species using electrospray ionization (ESI) coupled to collision induced dissociation (CID) and newly employed ultraviolet photodissociation (UVPD) methods. Our MS protocols allow for unequivocal determination of chemical structure, paramount to characterization of lipid A molecules that contain unique or novel chemical modifications. We also describe the radioisotopic labeling, and subsequent isolation, of lipid A from bacterial cells for analysis by TLC. Relative to MS-based protocols, TLC provides a more economical and rapid characterization method, but cannot be used to unambiguously assign lipid A chemical structures without the use of standards of known chemical structure. Over the last two decades isolation and characterization of lipid A has led to numerous exciting discoveries that have improved our understanding of the physiology of gram-negative bacteria, mechanisms of antibiotic resistance, the human innate immune response, and have provided many new targets in the development of antibacterial compounds.
Chemistry, Issue 79, Membrane Lipids, Toll-Like Receptors, Endotoxins, Glycolipids, Lipopolysaccharides, Lipid A, Microbiology, Lipids, lipid A, Bligh-Dyer, thin layer chromatography (TLC), lipopolysaccharide, mass spectrometry, Collision Induced Dissociation (CID), Photodissociation (PD)
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DNBS/TNBS Colitis Models: Providing Insights Into Inflammatory Bowel Disease and Effects of Dietary Fat
Authors: Vijay Morampudi, Ganive Bhinder, Xiujuan Wu, Chuanbin Dai, Ho Pan Sham, Bruce A. Vallance, Kevan Jacobson.
Institutions: BC Children's Hospital.
Inflammatory Bowel Diseases (IBD), including Crohn's Disease and Ulcerative Colitis, have long been associated with a genetic basis, and more recently host immune responses to microbial and environmental agents. Dinitrobenzene sulfonic acid (DNBS)-induced colitis allows one to study the pathogenesis of IBD associated environmental triggers such as stress and diet, the effects of potential therapies, and the mechanisms underlying intestinal inflammation and mucosal injury. In this paper, we investigated the effects of dietary n-3 and n-6 fatty acids on the colonic mucosal inflammatory response to DNBS-induced colitis in rats. All rats were fed identical diets with the exception of different types of fatty acids [safflower oil (SO), canola oil (CO), or fish oil (FO)] for three weeks prior to exposure to intrarectal DNBS. Control rats given intrarectal ethanol continued gaining weight over the 5 day study, whereas, DNBS-treated rats fed lipid diets all lost weight with FO and CO fed rats demonstrating significant weight loss by 48 hr and rats fed SO by 72 hr. Weight gain resumed after 72 hr post DNBS, and by 5 days post DNBS, the FO group had a higher body weight than SO or CO groups. Colonic sections collected 5 days post DNBS-treatment showed focal ulceration, crypt destruction, goblet cell depletion, and mucosal infiltration of both acute and chronic inflammatory cells that differed in severity among diet groups. The SO fed group showed the most severe damage followed by the CO, and FO fed groups that showed the mildest degree of tissue injury. Similarly, colonic myeloperoxidase (MPO) activity, a marker of neutrophil activity was significantly higher in SO followed by CO fed rats, with FO fed rats having significantly lower MPO activity. These results demonstrate the use of DNBS-induced colitis, as outlined in this protocol, to determine the impact of diet in the pathogenesis of IBD.
Medicine, Issue 84, Chemical colitis, Inflammatory Bowel Disease, intra rectal administration, intestinal inflammation, transmural inflammation, myeloperoxidase activity
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Biosensor for Detection of Antibiotic Resistant Staphylococcus Bacteria
Authors: Rajesh Guntupalli, Iryna Sorokulova, Eric Olsen, Ludmila Globa, Oleg Pustovyy, Vitaly Vodyanoy.
Institutions: Auburn University , Keesler Air Force Base.
A structurally transformed lytic bacteriophage having a broad host range of Staphylococcus aureus strains and a penicillin-binding protein (PBP 2a) antibody conjugated latex beads have been utilized to create a biosensor designed for discrimination of methicillin resistant (MRSA) and sensitive (MSSA) S. aureus species 1,2. The lytic phages have been converted into phage spheroids by contact with water-chloroform interface. Phage spheroid monolayers have been moved onto a biosensor surface by Langmuir-Blodgett (LB) technique 3. The created biosensors have been examined by a quartz crystal microbalance with dissipation tracking (QCM-D) to evaluate bacteria-phage interactions. Bacteria-spheroid interactions led to reduced resonance frequency and a rise in dissipation energy for both MRSA and MSSA strains. After the bacterial binding, these sensors have been further exposed to the penicillin-binding protein antibody latex beads. Sensors analyzed with MRSA responded to PBP 2a antibody beads; although sensors inspected with MSSA gave no response. This experimental distinction determines an unambiguous discrimination between methicillin resistant and sensitive S. aureus strains. Equally bound and unbound bacteriophages suppress bacterial growth on surfaces and in water suspensions. Once lytic phages are changed into spheroids, they retain their strong lytic activity and show high bacterial capture capability. The phage and phage spheroids can be utilized for testing and sterilization of antibiotic resistant microorganisms. Other applications may include use in bacteriophage therapy and antimicrobial surfaces.
Bioengineering, Issue 75, Microbiology, Infectious Diseases, Infection, Medicine, Immunology, Cellular Biology, Molecular Biology, Genetics, Anatomy, Physiology, Bacteria, Pharmacology, Staphylococcus, Bacteriophages, phage, Binding, Competitive, Biophysics, surface properties (nonmetallic materials), surface wave acoustic devices (electronic design), sensors, Lytic phage spheroids, QCM-D, Langmuir-Blodgett (LB) monolayers, MRSA, Staphylococcus aureus, assay
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Measuring Oral Fatty Acid Thresholds, Fat Perception, Fatty Food Liking, and Papillae Density in Humans
Authors: Rivkeh Y. Haryono, Madeline A. Sprajcer, Russell S. J. Keast.
Institutions: Deakin University.
Emerging evidence from a number of laboratories indicates that humans have the ability to identify fatty acids in the oral cavity, presumably via fatty acid receptors housed on taste cells. Previous research has shown that an individual's oral sensitivity to fatty acid, specifically oleic acid (C18:1) is associated with body mass index (BMI), dietary fat consumption, and the ability to identify fat in foods. We have developed a reliable and reproducible method to assess oral chemoreception of fatty acids, using a milk and C18:1 emulsion, together with an ascending forced choice triangle procedure. In parallel, a food matrix has been developed to assess an individual's ability to perceive fat, in addition to a simple method to assess fatty food liking. As an added measure tongue photography is used to assess papillae density, with higher density often being associated with increased taste sensitivity.
Neuroscience, Issue 88, taste, overweight and obesity, dietary fat, fatty acid, diet, fatty food liking, detection threshold
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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
Authors: Chryssostomos Chatgilialoglu, Carla Ferreri, Annalisa Masi, Michele Melchiorre, Anna Sansone, Michael A. Terzidis, Armida Torreggiani.
Institutions: Consiglio Nazionale delle Ricerche.
The involvement of free radicals in life sciences has constantly increased with time and has been connected to several physiological and pathological processes. This subject embraces diverse scientific areas, spanning from physical, biological and bioorganic chemistry to biology and medicine, with applications to the amelioration of quality of life, health and aging. Multidisciplinary skills are required for the full investigation of the many facets of radical processes in the biological environment and chemical knowledge plays a crucial role in unveiling basic processes and mechanisms. We developed a chemical biology approach able to connect free radical chemical reactivity with biological processes, providing information on the mechanistic pathways and products. The core of this approach is the design of biomimetic models to study biomolecule behavior (lipids, nucleic acids and proteins) in aqueous systems, obtaining insights of the reaction pathways as well as building up molecular libraries of the free radical reaction products. This context can be successfully used for biomarker discovery and examples are provided with two classes of compounds: mono-trans isomers of cholesteryl esters, which are synthesized and used as references for detection in human plasma, and purine 5',8-cyclo-2'-deoxyribonucleosides, prepared and used as reference in the protocol for detection of such lesions in DNA samples, after ionizing radiations or obtained from different health conditions.
Chemistry, Issue 74, Biochemistry, Chemical Engineering, Chemical Biology, chemical analysis techniques, chemistry (general), life sciences, radiation effects (biological, animal and plant), biomarker, biomimetic chemistry, free radicals, trans lipids, cyclopurine lesions, DNA, chromatography, spectroscopy, synthesis
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Following in Real Time the Impact of Pneumococcal Virulence Factors in an Acute Mouse Pneumonia Model Using Bioluminescent Bacteria
Authors: Malek Saleh, Mohammed R. Abdullah, Christian Schulz, Thomas Kohler, Thomas Pribyl, Inga Jensch, Sven Hammerschmidt.
Institutions: University of Greifswald.
Pneumonia is one of the major health care problems in developing and industrialized countries and is associated with considerable morbidity and mortality. Despite advances in knowledge of this illness, the availability of intensive care units (ICU), and the use of potent antimicrobial agents and effective vaccines, the mortality rates remain high1. Streptococcus pneumoniae is the leading pathogen of community-acquired pneumonia (CAP) and one of the most common causes of bacteremia in humans. This pathogen is equipped with an armamentarium of surface-exposed adhesins and virulence factors contributing to pneumonia and invasive pneumococcal disease (IPD). The assessment of the in vivo role of bacterial fitness or virulence factors is of utmost importance to unravel S. pneumoniae pathogenicity mechanisms. Murine models of pneumonia, bacteremia, and meningitis are being used to determine the impact of pneumococcal factors at different stages of the infection. Here we describe a protocol to monitor in real-time pneumococcal dissemination in mice after intranasal or intraperitoneal infections with bioluminescent bacteria. The results show the multiplication and dissemination of pneumococci in the lower respiratory tract and blood, which can be visualized and evaluated using an imaging system and the accompanying analysis software.
Infection, Issue 84, Gram-Positive Bacteria, Streptococcus pneumoniae, Pneumonia, Bacterial, Respiratory Tract Infections, animal models, community-acquired pneumonia, invasive pneumococcal diseases, Pneumococci, bioimaging, virulence factor, dissemination, bioluminescence, IVIS Spectrum
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Determination of Tolerable Fatty Acids and Cholera Toxin Concentrations Using Human Intestinal Epithelial Cells and BALB/c Mouse Macrophages
Authors: Farshad Tamari, Joanna Tychowski, Laura Lorentzen.
Institutions: Kingsborough Community College, University of Texas at Austin, Kean University.
The positive role of fatty acids in the prevention and alleviation of non-human and human diseases have been and continue to be extensively documented. These roles include influences on infectious and non-infectious diseases including prevention of inflammation as well as mucosal immunity to infectious diseases. Cholera is an acute intestinal illness caused by the bacterium Vibrio cholerae. It occurs in developing nations and if left untreated, can result in death. While vaccines for cholera exist, they are not always effective and other preventative methods are needed. We set out to determine tolerable concentrations of three fatty acids (oleic, linoleic and linolenic acids) and cholera toxin using mouse BALB/C macrophages and human intestinal epithelial cells, respectively. We solubilized the above fatty acids and used cell proliferation assays to determine the concentration ranges and specific concentrations of the fatty acids that are not detrimental to human intestinal epithelial cell viability. We solubilized cholera toxin and used it in an assay to determine the concentration ranges and specific concentrations of cholera toxin that do not statistically decrease cell viability in BALB/C macrophages. We found the optimum fatty acid concentrations to be between 1-5 ng/μl, and that for cholera toxin to be < 30 ng per treatment. This data may aid future studies that aim to find a protective mucosal role for fatty acids in prevention or alleviation of cholera infections.
Infection, Issue 75, Medicine, Immunology, Infectious Diseases, Microbiology, Molecular Biology, Cellular Biology, Biochemistry, Bioengineering, Bacterial Infections and Mycoses, Mucosal immunity, oleic acid, linoleic acid, linolenic acid, cholera toxin, cholera, fatty acids, tissue culture, MTT assay, mouse, animal model
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Studying Interactions of Staphylococcus aureus with Neutrophils by Flow Cytometry and Time Lapse Microscopy
Authors: Bas G.J. Surewaard, Jos A.G. van Strijp, Reindert Nijland.
Institutions: University Medical Center Utrecht.
We present methods to study the effect of phenol soluble modulins (PSMs) and other toxins produced and secreted by Staphylococcus aureus on neutrophils. To study the effects of the PSMs on neutrophils we isolate fresh neutrophils using density gradient centrifugation. These neutrophils are loaded with a dye that fluoresces upon calcium mobilization. The activation of neutrophils by PSMs initiates a rapid and transient increase in the free intracellular calcium concentration. In a flow cytometry experiment this rapid mobilization can be measured by monitoring the fluorescence of a pre-loaded dye that reacts to the increased concentration of free Ca2+. Using this method we can determine the PSM concentration necessary to activate the neutrophil, and measure the effects of specific and general inhibitors of the neutrophil activation. To investigate the expression of the PSMs in the intracellular space, we have constructed reporter fusions of the promoter of the PSMα operon to GFP. When these reporter strains of S. aureus are phagocytosed by neutrophils, the induction of expression can be observed using fluorescence microscopy.
Infection, Issue 77, Immunology, Cellular Biology, Infectious Diseases, Microbiology, Genetics, Medicine, Biomedical Engineering, Bioengineering, Neutrophils, Staphylococcus aureus, Bacterial Toxins, Microscopy, Fluorescence, Time-Lapse Imaging, Phagocytosis, phenol soluble modulins, PSMs, Polymorphonuclear Neutrophils, PMNs, intracellular expression, time-lapse microscopy, flow cytometry, cell, isolation, cell culture
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A Toolkit to Enable Hydrocarbon Conversion in Aqueous Environments
Authors: Eva K. Brinkman, Kira Schipper, Nadine Bongaerts, Mathias J. Voges, Alessandro Abate, S. Aljoscha Wahl.
Institutions: Delft University of Technology, Delft University of Technology.
This work puts forward a toolkit that enables the conversion of alkanes by Escherichia coli and presents a proof of principle of its applicability. The toolkit consists of multiple standard interchangeable parts (BioBricks)9 addressing the conversion of alkanes, regulation of gene expression and survival in toxic hydrocarbon-rich environments. A three-step pathway for alkane degradation was implemented in E. coli to enable the conversion of medium- and long-chain alkanes to their respective alkanols, alkanals and ultimately alkanoic-acids. The latter were metabolized via the native β-oxidation pathway. To facilitate the oxidation of medium-chain alkanes (C5-C13) and cycloalkanes (C5-C8), four genes (alkB2, rubA3, rubA4and rubB) of the alkane hydroxylase system from Gordonia sp. TF68,21 were transformed into E. coli. For the conversion of long-chain alkanes (C15-C36), theladA gene from Geobacillus thermodenitrificans was implemented. For the required further steps of the degradation process, ADH and ALDH (originating from G. thermodenitrificans) were introduced10,11. The activity was measured by resting cell assays. For each oxidative step, enzyme activity was observed. To optimize the process efficiency, the expression was only induced under low glucose conditions: a substrate-regulated promoter, pCaiF, was used. pCaiF is present in E. coli K12 and regulates the expression of the genes involved in the degradation of non-glucose carbon sources. The last part of the toolkit - targeting survival - was implemented using solvent tolerance genes, PhPFDα and β, both from Pyrococcus horikoshii OT3. Organic solvents can induce cell stress and decreased survivability by negatively affecting protein folding. As chaperones, PhPFDα and β improve the protein folding process e.g. under the presence of alkanes. The expression of these genes led to an improved hydrocarbon tolerance shown by an increased growth rate (up to 50%) in the presences of 10% n-hexane in the culture medium were observed. Summarizing, the results indicate that the toolkit enables E. coli to convert and tolerate hydrocarbons in aqueous environments. As such, it represents an initial step towards a sustainable solution for oil-remediation using a synthetic biology approach.
Bioengineering, Issue 68, Microbiology, Biochemistry, Chemistry, Chemical Engineering, Oil remediation, alkane metabolism, alkane hydroxylase system, resting cell assay, prefoldin, Escherichia coli, synthetic biology, homologous interaction mapping, mathematical model, BioBrick, iGEM
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Combined In vivo Optical and µCT Imaging to Monitor Infection, Inflammation, and Bone Anatomy in an Orthopaedic Implant Infection in Mice
Authors: Nicholas M. Bernthal, Brad N. Taylor, Jeffrey A. Meganck, Yu Wang, Jonathan H. Shahbazian, Jared A. Niska, Kevin P. Francis, Lloyd S. Miller.
Institutions: David Geffen School of Medicine at University of California, Los Angeles (UCLA), PerkinElmer, Johns Hopkins University School of Medicine, Johns Hopkins University School of Medicine.
Multimodality imaging has emerged as a common technological approach used in both preclinical and clinical research. Advanced techniques that combine in vivo optical and μCT imaging allow the visualization of biological phenomena in an anatomical context. These imaging modalities may be especially useful to study conditions that impact bone. In particular, orthopaedic implant infections are an important problem in clinical orthopaedic surgery. These infections are difficult to treat because bacterial biofilms form on the foreign surgically implanted materials, leading to persistent inflammation, osteomyelitis and eventual osteolysis of the bone surrounding the implant, which ultimately results in implant loosening and failure. Here, a mouse model of an infected orthopaedic prosthetic implant was used that involved the surgical placement of a Kirschner-wire implant into an intramedullary canal in the femur in such a way that the end of the implant extended into the knee joint. In this model, LysEGFP mice, a mouse strain that has EGFP-fluorescent neutrophils, were employed in conjunction with a bioluminescent Staphylococcus aureus strain, which naturally emits light. The bacteria were inoculated into the knee joints of the mice prior to closing the surgical site. In vivo bioluminescent and fluorescent imaging was used to quantify the bacterial burden and neutrophil inflammatory response, respectively. In addition, μCT imaging was performed on the same mice so that the 3D location of the bioluminescent and fluorescent optical signals could be co-registered with the anatomical μCT images. To quantify the changes in the bone over time, the outer bone volume of the distal femurs were measured at specific time points using a semi-automated contour based segmentation process. Taken together, the combination of in vivo bioluminescent/fluorescent imaging with μCT imaging may be especially useful for the noninvasive monitoring of the infection, inflammatory response and anatomical changes in bone over time.
Infection, Issue 92, imaging, optical, CT, bioluminescence, fluorescence, staphylococcus, infection, inflammation, bone, orthopaedic, implant, biofilm
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Use of Arabidopsis eceriferum Mutants to Explore Plant Cuticle Biosynthesis
Authors: Lacey Samuels, Allan DeBono, Patricia Lam, Miao Wen, Reinhard Jetter, Ljerka Kunst.
Institutions: University of British Columbia - UBC, University of British Columbia - UBC.
The plant cuticle is a waxy outer covering on plants that has a primary role in water conservation, but is also an important barrier against the entry of pathogenic microorganisms. The cuticle is made up of a tough crosslinked polymer called "cutin" and a protective wax layer that seals the plant surface. The waxy layer of the cuticle is obvious on many plants, appearing as a shiny film on the ivy leaf or as a dusty outer covering on the surface of a grape or a cabbage leaf thanks to light scattering crystals present in the wax. Because the cuticle is an essential adaptation of plants to a terrestrial environment, understanding the genes involved in plant cuticle formation has applications in both agriculture and forestry. Today, we'll show the analysis of plant cuticle mutants identified by forward and reverse genetics approaches.
Plant Biology, Issue 16, Annual Review, Cuticle, Arabidopsis, Eceriferum Mutants, Cryso-SEM, Gas Chromatography
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