The authors thank Therwa Hamza, John E. Tidwell, Nina Clovis, and Suzanne Smith for experimental assistance and Suzanne Smith for proofreading. The authors also thank John Thomas, PhD for providing the bacterial clinical isolates and John B. Barnett, PhD for his support and the use of the biological safety lab at the Department of Microbiology, Immunology and Cell Biology at West Virginia University. The authors acknowledge financial support from the Osteosynthesis and Trauma Care Foundation and National Science Foundation (#1003907). Microscope experiments and image analysis were also performed in the West Virginia University Imaging Facility, which is supported in part by the Mary Babb Randolph Cancer Center and NIH grant P20 RR016440.
Animal use for blood draws were approved by the West Virginia University Institutional Animal Care and Use Committee. All experiments were executed in compliance with all relevant guidelines, regulations, and regulatory agencies.

1. Preparation and Activation of PRP
1.1 Blood draw
<ol>
	<li>Anesthetize rabbit by inhalation of isoflurane (2% in O2 for induction and 1% for maintenance).</li>
	<li>Draw 2 ml 0.129 M tri-sodium citrate (an anticoagulent solution) into a 20 ml syringe. The tri-sodium citrate solution is prepared by dissolving 1.897 g tri-sodium citrate in 50 ml distilled H2O and filtering with a 0.22 &mu;m sterile filter.</li>
	<li>Sterilize the rabbit ear using 70% ethanol.</li>
	<li>Draw blood (e.g. 5 ml) from the rabbit ear vein via a butterfly needle (25 G) connected to the syringe.</li>
	<li>Mix the blood with the tri-sodium citrate solution by gentle agitation. The volume ratio of blood and tri-sodium citrate solution is 9:1.</li>
</ol>
1.2 PRP preparation (Figure 1)
<ol>
	<li>Transfer the anticoagulated blood to a 50 ml plastic centrifuge tube. Take an aliquot of 10 &mu;l blood to determine the baseline platelet count using hemocytometry.</li>
	<li>Centrifuge the blood at 300 x g for 10 min at room temperature (RT) in a centrifuge with a swing-out rotor. Set the acceleration and brake velocity to low (Figure 1).</li>
	<li>After centrifugation, the blood is separated into three layers. The bottom layer is mainly red blood cells, the middle layer (commonly referred to as the "buffy coat") is composed of concentrated platelets and leukocytes, and the top layer is mainly plasma, which is the liquid component of blood, and platelets (Figure 1). Carefully transport the centrifuge tube to a cell culture hood; do not disturb the layers. Transfer all of the plasma, buffy coat, and 2-3 mm thick red blood cell layer into a 15 ml plastic tube using a 1 ml plastic pipettor.</li>
	<li>Centrifuge the transferred sample a second time at 3,000 x g for 15 min at RT. The top layer (supernatant) is considered platelet poor plasma (PPP) and is transferred to a new tube.</li>
	<li>Obtain PRP by adjusting the platelet concentration in the remaining blood sample using PPP to obtain 2.0 x 106 platelets/&mu;l (determined by hemocytometry).</li>
</ol>
1.3 PRP activation
<ol>
	<li>Prepare PRP activation solution by dissolving 5,000 IU bovine thrombin with 5 ml 10% calcium chloride to the working concentration of 1,000 IU/ml.</li>
	<li>Add the activation solution to PRP and PPP, and mix the solution by repeatedly pipetting to form PRP- and PPP-gels. The volume ratio of the activation solution to PRP or PPP is 1:4.</li>
</ol>
2. In vitro Antimicrobial Test of PRP Using Kill Curve Assay (Figure 2)
<ol>
	<li>Using a sterile inoculating loop, add several colonies of S. aureus from its overnight plate culture into 5 ml of Mueller Hinton broth (MHB) in a plastic tube. Vortex briefly and then incubate the sample for 2 hr at 37 &deg;C. Next, the optical density of the bacterial media was determined using a spectrophotometer and adjusted to an optical density equal to ~1 x 108 CFU/ml based on the pre-determined standard curve.</li>
	<li>Make a 100x dilution using PBS to obtain 1 x 106 CFU/ml and place the inoculums on ice.</li>
	<li>Set up and label sterile, disposable 5 ml round-bottom polystyrene tubes, and prepare the following sample groups as indicated in Table 1 for a final volume of 2 ml in each tube.</li>
	<li>Add PRP, PPP, or PBS first to the polystyrene tubes, followed by the thrombin solution for activation (gel formation). Next, add MHB and then the S. aureus inoculums (1 x 106 CFU/ml) to obtain the final concentration of 1 x 105 CFU/ml.</li>
	<li>Incubate the tubes at 37 &deg;C with orbital agitation at 150 rpm.</li>
	<li>At pre-determined time points (e.g. 0, 1, and 2 hr), mix the solutions in each tube via repeat pipetting (this step is important since bacteria may be trapped inside the PRP gel). Take 10 &mu;l of sample, dilute serially with sterile 0.9% saline, and pipette a 100 &mu;l aliquot of each dilution onto a Tryptic soy agar (TSA, with 5% sheep blood) plate for CFU counting.</li>
	<li>Culture the agar plates overnight at 37 &deg;C, then count and record the plate colonies. Plot data on a logarithimic scale with time (hr) on the x-axis and CFU/ml on the y-axis.</li>
</ol>

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The authors declare that they have no competing financial interests.

Platelet-rich plasma has been increasingly used for clinical applications due to its healing-promoting properties 15-17. In the present study, PRP was presented as a new approach for infection prevention. PRP was found to have strong antimicrobial properties against MRSA, MSSA, Group A Streptococcus, and Neisseria gonorrhoeae. The major advantages of PRP, compared to conventional antibiotic treatments, for infection prevention include: (1) Current antibiotic therapies are facing challenges in...

Implant-associated infection is a significant clinical complication. Staphylococcus aureus (S. aureus) is one of the most common microorganisms isolated from implant-associated infections. It is capable of producing a biofilm that covers the surfaces of implants and may lead to antibiotic-resistant infection 1,2. Treatment of implant-associated infection frequently requires long-term hospitalization for repeated debridements and prolonged parenteral antibiotic therapy. In antibiotic resistant cases, removal of the implant may be necessary. The rising resistance of bacteria to antibiotics has also been referred to by the Centers for Disease Control and Prevention (CDC) as "one of the world's most pressing health problems." In time, without the development of new and effective antimicrobial treatments, it is possible that multi-drug resistant pathogens will be untreatable with conventional antibiotics. Prevention of implant-associated infection is therefore important and novel prophylactic agents or approaches are needed for preventing such infections.
Platelet-rich plasma (PRP) is a concentration of autologous blood that contains over 30 growth factors which can help with bone and bone graft healing 3-5. The application of PRP to enhance bone regeneration and soft tissue maturation has been increasingly reported in clinics because of its high concentration of various growth factors released by platelets.
Several characteristics of PRP indicate that PRP may also have antimicrobial properties 6-9. PRP contains a large number of platelets, a high concentration of leukocytes (which may possess host-defense actions against bacteria and fungi), and multiple antimicrobial peptides 7,8,10. In a recent study of a large cohort of cardiac surgical patients, it was revealed that the intraoperative use of PRP-gel during wound closure significantly decreased the incidence of superficial and deep sternum infection 11. For these reasons and observations, we hypothesized that PRP, besides its well-studied healing-promoting properties, has antimicrobial properties. The potential advantages of using PRP to prevent infection may include: (i) PRP is less likely to induce resistance compared to conventional antibiotic treatments. (ii) PRP also has properties that promote healing which may have a synergistic effect on infection prevention; PRP's healing-promoting properties could provide a seal to prevent bacterial attachment thereby reducing the odds for infection as pathogens and human cells are racing for implant surfaces 12,13. (iii) PRP is inherently biocompatible, and safe and free from the risk of transmissible diseases.
Our long-term goal is to use PRP as a new approach to prevent implant-associated infections. The aim of this study was to prepare PRP using a twice centrifugation approach, to examine PRP's in vitro antimicrobial properties, and to describe the protocols for evaluating such antimicrobial properties.

<table border="1">
 <tbody>
 <tr>
 <td>Name of Reagent/Material</td>
 <td>Company</td>
 <td>Catalog Number</td>
 <td>Comments</td>
 </tr>
 <tr>
 <td>Bovine thrombin</td>
 <td>King Pharmaceuticals, Inc </td>
 <td>60793-215-05</td>
 <td>Thrombin (bovine origin)</td>
 </tr>
 <tr>
 <td>Calcium chloride</td>
 <td>King Pharmaceuticals, Inc</td>
 <td>60793-215-05</td>
 <td>10% calcium chloride</td>
 </tr>
 <tr>
 <td>Ethanol</td>
 <td>Sigma-Aldrich</td>
 <td>E7023</td>
 <td></td>
 </tr>
 <tr>
 <td>Isoflurane</td>
 <td>Baxter</td>
 <td>1001936060</td>
 <td></td>
 </tr>
 <tr>
 <td>Mueller Hinton broth</td>
 <td>Becton, Dickinson and Company</td>
 <td>275710</td>
 <td></td>
 </tr>
 <tr>
 <td>Phosphate-buffered saline</td>
 <td>Sigma-Aldrich</td>
 <td>D8662</td>
 <td></td>
 </tr>
 <tr>
 <td>Tri-sodium citrate</td>
 <td>Sigma-Aldrich</td>
 <td>W302600</td>
 <td></td>
 </tr>
 <tr>
 <td>Tryptic soy agar</td>
 <td>Fisher Scientific</td>
 <td>R01202</td>
 <td></td>
 </tr>
 <tr>
 <td>Centrifuge</td>
 <td>Kendro Laboratory Products</td>
 <td>750043077</td>
 <td></td>
 </tr>
 <tr>
 <td>Syringe filter</td>
 <td>Millipore</td>
 <td>SLGP033RS</td>
 <td></td>
 </tr>
 </tbody>
</table>

prp as a new approach to prevent infection: preparation and in vitro antimicrobial properties of prp

Implant-associated infection is becoming more and more challenging to the healthcare industry worldwide due to increasing antibiotic resistance, transmission of antibiotic resistant bacteria between animals and humans, and the high cost of treating infections.
In this study, we disclose a new strategy that may be effective in preventing implant-associated infection based on the potential antimicrobial properties of platelet-rich plasma (PRP). Due to its well-studied properties for promoting healing, PRP (a biological product) has been increasingly used for clinical applications including orthopaedic surgeries, periodontal and oral surgeries, maxillofacial surgeries, plastic surgeries, sports medicine, etc.
PRP could be an advanced alternative to conventional antibiotic treatments in preventing implant-associated infections. The use of PRP may be advantageous compared to conventional antibiotic treatments since PRP is less likely to induce antibiotic resistance and PRP's antimicrobial and healing-promoting properties may have a synergistic effect on infection prevention. It is well known that pathogens and human cells are racing for implant surfaces, and PRP's properties of promoting healing could improve human cell attachment thereby reducing the odds for infection. In addition, PRP is inherently biocompatible, and safe and free from the risk of transmissible diseases.
For our study, we have selected several clinical bacterial strains that are commonly found in orthopaedic infections and examined whether PRP has in vitro antimicrobial properties against these bacteria. We have prepared PRP using a twice centrifugation approach which allows the same platelet concentration to be obtained for all samples. We have achieved consistent antimicrobial findings and found that PRP has strong in vitro antimicrobial properties against bacteria like methicillin-sensitive and methicillin-resistant Staphylococcus aureus, Group A Streptococcus, and Neisseria gonorrhoeae. Therefore, the use of PRP may have the potential to prevent infection and to reduce the need for costly post-operative treatment of implant-associated infections.

PRP is reproducibly prepared using a twice centrifugation approach (Figure 1). PRP is found to present strong (up to 100-fold reduction in CFUs) in vitro antimicrobial properties against methicillin resistant S. aureus (MRSA) (Figure 3), which is commonly found in hospitals worldwide 14. Similarly, PRP has strong antimicrobial properties against methicillin sensitive S. aureus (MSSA), Group A Streptococcus, and Neisseria gonorrhoeae...

Watch this Scientific Journal Video about PRP as a New Approach to Prevent Infection: Preparation and In vitro Antimicrobial Properties of PRP at JoVE.com

PRP as a New Approach to Prevent Infection: Preparation and In vitro Antimicrobial Properties of PRP

Implant-associated infection is a significant clinical complication. This study describes an approach using platelet-rich plasma (PRP) to prevent implant-associated infections, presents the protocol for preparing PRP with constant platelet concentration, and reports the newly identified antimicrobial properties of PRP and related protocols for examining such antimicrobial properties in vitro.

PRP as a New Approach to Prevent Infection: Preparation and In vitro Antimicrobial Properties of PRP

Implant-associated infection is becoming more and more challenging to the healthcare industry worldwide due to increasing antibiotic resistance, ...

prp-as-new-approach-to-prevent-infection-preparation-vitro

Research

JoVE Journal

Immunology and Infection

21.2K vues.  West Virginia University. Implant associée à l'infection est une complication clinique importante. Cette étude décrit une approche basée sur plasma riche en plaquettes (PRP) pour prévenir les infections associées aux implants, présente le protocole pour la préparation de PRP avec la concentration de plaquettes constante, et rend compte des propriétés nouvellement identifiés antimicrobiennes de PRP et les protocoles connexes pour examiner de telles propriétés antimicrobiennes

Vidéo: PRP as a New Approach to Prevent Infection: Preparation and In vitro Antimicrobial Properties of PRP

Retroviral Transduction of T-cell Receptors in Mouse T-cells

T-cell receptors (TCRs) play a central role in the immune system. TCRs on T-cell surfaces can specifically recognize peptide antigens presented by antigen presenting cells (APCs)1. This recognition leads to the activation of T-cells and a series of functional outcomes (e.g. cytokine production, killing of the target cells). Understanding the functional role of TCRs is critical to harness the power of the immune system to treat a variety of immunology related diseases (e.g. cancer or autoimmunity).
It is convenient to study TCRs in mouse models, which can be accomplished in several ways. Making TCR transgenic mouse models is costly and time-consuming and currently there are only a limited number of them available2-4. Alternatively, mice with antigen-specific T-cells can be generated by bone marrow chimera. This method also takes several weeks and requires expertise5. Retroviral transduction of TCRs into in vitro activated mouse T-cells is a quick and relatively easy method to obtain T-cells of desired peptide-MHC specificity. Antigen-specific T-cells can be generated in one week and used in any downstream applications. Studying transduced T-cells also has direct application to human immunotherapy, as adoptive transfer of human T-cells transduced with antigen-specific TCRs is an emerging strategy for cancer treatment6.
Here we present a protocol to retrovirally transduce TCRs into in vitro activated mouse T-cells. Both human and mouse TCR genes can be used. Retroviruses carrying specific TCR genes are generated and used to infect mouse T-cells activated with anti-CD3 and anti-CD28 antibodies. After in vitro expansion, transduced T-cells are analyzed by flow cytometry.

We present a protocol to produce antigen-specific mouse T-cells using retroviral transduction

T-cell receptors (TCRs) play a central role in the immune system. TCRs on T-cell surfaces can specifically recognize peptide antigens presented by antigen ...

Introducing Shear Stress in the Study of Bacterial Adhesion

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the initial and determining step of the pathogenesis. Although experimentally adhesion is mostly studied in static conditions adhesion actually takes place in the presence of flowing liquid. First encounters between bacteria and their host often occur at the mucosal level, mouth, lung, gut, eye, etc. where mucus flows along the surface of epithelial cells. Later in infection, pathogens occasionally access the blood circulation causing life-threatening illnesses such as septicemia, sepsis and meningitis. A defining feature of these infections is the ability of these pathogens to interact with endothelial cells in presence of circulating blood. The presence of flowing liquid, mucus or blood for instance, determines adhesion because it generates a mechanical force on the pathogen. To characterize the effect of flowing liquid one usually refers to the notion of shear stress, which is the tangential force exerted per unit area by a fluid moving near a stationary wall, expressed in dynes/cm2. Intensities of shear stress vary widely according to the different vessels type, size, organ, location etc. (0-100 dynes/cm2). Circulation in capillaries can reach very low shear stress values and even temporarily stop during periods ranging between a few seconds to several minutes 1. On the other end of the spectrum shear stress in arterioles can reach 100 dynes/cm2 2. The impact of shear stress on different biological processes has been clearly demonstrated as for instance during the interaction of leukocytes with the endothelium 3. To take into account this mechanical parameter in the process of bacterial adhesion we took advantage of an experimental procedure based on the use of a disposable flow chamber 4. Host cells are grown in the flow chamber and fluorescent bacteria are introduced in the flow controlled by a syringe pump. We initially focused our investigations on the bacterial pathogen Neisseria meningitidis, a Gram-negative bacterium responsible for septicemia and meningitis. The procedure described here allowed us to study the impact of shear stress on the ability of the bacteria to: adhere to cells 1, to proliferate on the cell surface 5and to detach to colonize new sites 6 (Figure 1). Complementary technical information can be found in reference 7. Shear stress values presented here were chosen based on our previous experience1 and to represent values found in the literature. The protocol should be applicable to a wide range of pathogens with specific adjustments depending on the objectives of the study.

During the infection process, a key step is the adhesion of pathogens with host cells. In most instances this adhesion step occurs in the presence of mechanical stress generated by flowing liquid. We describe a technique that introduces shear stress as an important parameter in the study of bacterial adhesion.

During bacterial infections a sequence of interactions occur between the pathogen and its host. Bacterial adhesion to the host cell surface is often the ...

Simple and Robust in vivo and in vitro Approach for Studying Virus Assembly

In viruses with positive-sense RNA genomes pathogenic to humans, animals and plants, progeny encapsidation into mature and stable virions is a cardinal phase during establishment of infection in a given host. Consequently, study of encapsidation deciphers the information regarding the know-how of the mechanism regulating virus assembly to form infectious virions. Such information is vital in formulating novel methods of curbing virus spread and disease control. Virus encapsidation can be studied in vivo and in vitro. Genome encapsidation in vivo is a highly regulated selective process involving macromolecular interactions and subcellular compartmentalization. Therefore, study leading to dissect events encompassing virus encapsidation in vivo would provide basic knowledge to understand how viruses proliferate and assemble. Recently in vitro encapsidation has been exploited for the research in the area of biomedical imaging and therapeutic applications. Non-enveloped plant viruses stand far ahead in the venture of in vitro encapsidation of the negatively charged foreign material. Brome mosaic virus (BMV), a non-enveloped multicomponent RNA virus pathogenic to plants, has been used as a model system for studying genome packaging in vivo and in vitro. For encapsidation assays in Nicotiana benthamiana plants, Agrobacterium -mediated transient expression, refer to as agroinfiltration, is an efficient and robust technique for the synchronized delivery and expression of multiple components to the same cell. In this approach, a suspension of Agrobacterium tumefaciens cells carrying binary plasmid vectors carrying cDNAs of desiredviral mRNAs is infiltrated into the intercellular space withina leaf using nothing more sophisticated than a 1 ml disposable syringe (without needle). This process results in the transfer of DNA insert into plant cells; the T-DNA insert remains transiently in the nucleus and is then transcribed by the host polymerase II, leading to the transient expression. The resulting mRNA transcript (capped and polyadenylated) is then exported to the cytoplasm for translation. After approximately 24 to 48 hours of incubation,sections of infiltrated leaves can be sampled for microscopyor biochemical analyses. Agroinfiltration permits large numbers (hundreds to thousands) of cells to be transfected simultaneously. For in vitro encapsidation, purified virions of BMV are dissociated into capsid protein by dialyzing against dissociation buffer containing calcium chloride followed by removal of RNA and un-dissociated virions by centrifugation. Genome depleted capsid protein subunits are then reassembled with desired viral genome components or non-viral components such as indocyanine dye.

Simple and Robust in vivo and in vitro Approach for Studying Virus Assembly

A simple, efficient and robust way to synchronize the delivery of multiple viral components to plant cells via Agrobacterium-mediated transient expression is described. This approach is amenable for studying replication, encapsidation followed by in vitro reassembly of non-viral components into genome depleted optical viral ghosts suitable for biomedical applications.

In viruses with positive-sense RNA genomes pathogenic to humans, animals and plants, progeny encapsidation into mature and stable virions is a cardinal ...

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

There is growing concern about the relevance of in vitro antimicrobial susceptibility tests when applied to isolates of P. aeruginosa from cystic fibrosis (CF) patients. Existing methods rely on single or a few isolates grown aerobically and planktonically. Predetermined cut-offs are used to define whether the bacteria are sensitive or resistant to any given antibiotic1. However, during chronic lung infections in CF, P. aeruginosa populations exist in biofilms and there is evidence that the environment is largely microaerophilic2. The stark difference in conditions between bacteria in the lung and those during diagnostic testing has called into question the reliability and even relevance of these tests3.
 Artificial sputum medium (ASM) is a culture medium containing the components of CF patient sputum, including amino acids, mucin and free DNA. P. aeruginosa growth in ASM mimics growth during CF infections, with the formation of self-aggregating biofilm structures and population divergence4,5,6. The aim of this study was to develop a microtitre-plate assay to study antimicrobial susceptibility of P. aeruginosa based on growth in ASM, which is applicable to both microaerophilic and aerobic conditions.
 An ASM assay was developed in a microtitre plate format. P. aeruginosa biofilms were allowed to develop for 3 days prior to incubation with antimicrobial agents at different concentrations for 24 hours. After biofilm disruption, cell viability was measured by staining with resazurin. This assay was used to ascertain the sessile cell minimum inhibitory concentration (SMIC) of tobramycin for 15 different P. aeruginosa isolates under aerobic and microaerophilic conditions and SMIC values were compared to those obtained with standard broth growth. Whilst there was some evidence for increased MIC values for isolates grown in ASM when compared to their planktonic counterparts, the biggest differences were found with bacteria tested in microaerophilic conditions, which showed a much increased resistance up to a &gt;128 fold, towards tobramycin in the ASM system when compared to assays carried out in aerobic conditions.
 The lack of association between current susceptibility testing methods and clinical outcome has questioned the validity of current methods3. Several in vitro models have been used previously to study P. aeruginosa biofilms7, 8. However, these methods rely on surface attached biofilms, whereas the ASM biofilms resemble those observed in the CF lung9 . In addition, reduced oxygen concentration in the mucus has been shown to alter the behavior of P. aeruginosa2 and affect antibiotic susceptibility10. Therefore using ASM under microaerophilic conditions may provide a more realistic environment in which to study antimicrobial susceptibility.

Use of Artificial Sputum Medium to Test Antibiotic Efficacy Against Pseudomonas aeruginosa in Conditions More Relevant to the Cystic Fibrosis Lung

Current diagnostic antimicrobial susceptibility testing relies on the planktonic growth of isolates in nutrient rich, aerobic conditions. Here, we employ an alternative artificial sputum medium to study antimicrobial susceptibility of Pseudomonas aeruginosa biofilms under both aerobic and microaerophilic conditions more representative of the cystic fibrosis lung.

There  is growing concern about the relevance of in vitro antimicrobial  susceptibility tests when applied to isolates of P. aeruginosa from  cystic ...

An In vitro Model to Study Heterogeneity of Human Macrophage Differentiation and Polarization

Monocyte-derived macrophages represent an important cell type of the innate immune system. Mouse models studying macrophage biology suffer from the phenotypic and functional differences between murine and human monocyte-derived macrophages. Therefore, we here describe an in vitro model to generate and study primary human macrophages. Briefly, after density gradient centrifugation of peripheral blood drawn from a forearm vein, monocytes are isolated from peripheral blood mononuclear cells using negative magnetic bead isolation. These monocytes are then cultured for six days under specific conditions to induce different types of macrophage differentiation or polarization. The model is easy to use and circumvents the problems caused by species-specific differences between mouse and man. Furthermore, it is closer to the in vivo conditions than the use of immortalized cell lines. In conclusion, the model described here is suitable to study macrophage biology, identify disease mechanisms and novel therapeutic targets. Even though not fully replacing experiments with animals or human tissues obtained post mortem, the model described here allows identification and validation of disease mechanisms and therapeutic targets that may be highly relevant to various human diseases.

An In vitro Model to Study Heterogeneity of Human Macrophage Differentiation and Polarization

Monocyte-derived macrophages are important cells of the innate immune system. Here, we describe an easy to use in vitro model to generate these cells. Using gradient centrifugation, negative bead isolation and specific cell culture conditions, monocyte-derived macrophages can be generated for phenotypic and functional studies.

Monocyte-derived macrophages represent an important cell type of the innate immune system. Mouse models studying macrophage biology suffer from the ...

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection

Legionella pneumophila, the causative agent of a severe pneumonia named Legionnaires&#39; disease, is an important human pathogen that infects and replicates within alveolar macrophages. Its virulence depends on the Dot/Icm type IV secretion system (T4SS), which is essential to establish a replication permissive vacuole known as the Legionella containing vacuole (LCV). L. pneumophila infection can be modeled in mice however most mouse strains are not permissive, leading to the search for novel infection models. We have recently shown that the larvae of the wax moth Galleria mellonella are suitable for investigation of L. pneumophila infection. G. mellonella is increasingly used as an infection model for human pathogens and a good correlation exists between virulence of several bacterial species in the insect and in mammalian models. A key component of the larvae&#39;s immune defenses are hemocytes, professional phagocytes, which take up and destroy invaders. L. pneumophila is able to infect, form a LCV and replicate within these cells. Here we demonstrate protocols for analyzing L. pneumophila virulence in the G. mellonella model, including how to grow infectious L. pneumophila, pretreat the larvae with inhibitors, infect the larvae and how to extract infected cells for quantification and immunofluorescence microscopy. We also describe how to quantify bacterial replication and fitness in competition assays. These approaches allow for the rapid screening of mutants to determine factors important in L. pneumophila virulence, describing a new tool to aid our understanding of this complex pathogen.

Use of Galleria mellonella as a Model Organism to Study Legionella pneumophila Infection

The larva of the wax moth Galleria mellonella was recently established as an in vivo model to study Legionella pneumophila infection. Here, we demonstrate fundamental techniques to characterize the pathogenesis of Legionella in the larvae, including inoculation, measurement of bacterial virulence and replication as well as extraction and analysis of infected hemocytes.

Legionella pneumophila, the causative agent of a severe pneumonia named Legionnaires&#39; disease, is an important human pathogen that infects and ...

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact cellular functions, including energetics and signal transductions. While both fluorescent and electrophysiological methods, including electrode usage and patch-clamping, have been well developed for measuring these events in eukaryotic cells, methodology for measuring similar events in microorganisms have proven more challenging to develop given their small size in combination with the more complex outer surface of bacteria shielding the membrane. During our studies of death-initiation in Streptococcus pneumoniae (pneumococcus), we wanted to elucidate the role of membrane events, including changes in polarity, integrity, and intracellular ion concentrations. Searching the literature, we found that very few studies exist. Other investigators had monitored radioisotope uptake or equilibrium to measure ion fluxes and membrane potential and a limited number of studies, mostly in Gram-negative organisms, had seen some success using carbocyanine or oxonol fluorescent dyes to measure membrane potential, or loading bacteria with cell-permeant acetoxymethyl (AM) ester versions of ion-sensitive fluorescent indicator dyes. We therefore established and optimized protocols for measuring membrane potential, rupture, and ion-transport in the Gram-positive organism S. pneumoniae. We developed protocols using the bis-oxonol dye DiBAC4(3) and the cell-impermeant dye propidium iodide to measure membrane depolarization and rupture, respectively, as well as methods to optimally load the pneumococci with the AM esters of the ratiometric dyes Fura-2, PBFI, and BCECF to detect changes in intracellular concentrations of Ca2+, K+, and H+, respectively, using a fluorescence-detection plate reader. These protocols are the first of their kind for the pneumococcus and the majority of these dyes have not been used in any other bacterial species. Though our protocols have been optimized for S. pneumoniae, we believe these approaches should form an excellent starting-point for similar studies in other bacterial species.

Monitoring Changes in Membrane Polarity, Membrane Integrity, and Intracellular Ion Concentrations in Streptococcus pneumoniae Using Fluorescent Dyes

Unlike that seen for eukaryotes, there is a paucity of studies that detail membrane depolarization and ion concentration changes in bacteria, primarily as their small size makes conventional methods of measurement difficult. Here, we detail protocols for monitoring such events in the significant Gram-positive pathogen Streptococcus pneumoniae utilizing fluorescence techniques.

Membrane depolarization and ion fluxes are events that have been studied extensively in biological systems due to their ability to profoundly impact ...

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in mice. Recently, myeloid differentiation factor 88 (MyD88) signaling was shown to be important for initial T cell priming and memory T cell development during WNV NS4B-P38G mutant infection. In this study, two flow cytometry-based methods &#8211; an in vitro T cell priming assay and an intracellular cytokine staining (ICS) &#8211; were utilized to assess dendritic cells (DCs) and T cell functions. In the T cell priming assay, cell proliferation was analyzed by flow cytometry following co-culture of DCs from both groups of mice with carboxyfluorescein succinimidyl ester (CFSE) - labeled CD4+ T cells of OTII transgenic mice. This approach provided an accurate determination of the percentage of proliferating CD4+ T cells with significantly improved overall sensitivity than the traditional assays with radioactive reagents. A microcentrifuge tube system was used in both cell culture and cytokine staining procedures of the ICS protocol. Compared to the traditional tissue culture plate-based system, this modified procedure was easier to perform at biosafety level (BL) 3 facilities. Moreover, WNV- infected cells were treated with paraformaldehyde in both assays, which enabled further analysis outside BL3 facilities. Overall, these in vitro immunological assays can be used to efficiently assess cell-mediated immune responses during WNV infection.

In Vitro Analysis of Myd88-mediated Cellular Immune Response to West Nile Virus Mutant Strain Infection

Two flow cytometry-based methods &#8211; an in vitro T cell priming assay and intracellular cytokine staining were utilized to measure antigen presenting capacity of dendritic cells and antigen-specific T cell responses to a West Nile virus mutant infection in mice.

An attenuated West Nile virus (WNV), a nonstructural (NS) 4B-P38G mutant, induced higher innate cytokine and T cell responses than the wild-type WNV in ...

A Simple and Efficient Approach to Construct Mutant Vaccinia Virus Vectors

The CRISPR-associated endonuclease Cas9 can edit particular genomic loci directed by a single guide RNA (gRNA). The CRISPR/Cas9 system has been successfully employed for editing genomes of various organisms. Here we describe a protocol for editing the vaccinia virus (VV) genome in the cytoplasm of VV-infected CV-1 cells using the RNA-guided Cas9. RNA-guided Cas9 induces double-stranded DNA breaks facilitating homologous recombination efficiently and specifically in the targeted site of VV and a transgene can be incorporated into these sites by homologous recombination. By using a site-specific homologous vector with transgene(s), a N1L gene-deleted VV with the red fluorescence protein (RFP) gene incorporated in this region was generated with a successful recombination efficiency 10 times greater than that obtained from the conventional homologous recombination method. This protocol demonstrates successful use of RNA-guided Cas9 system to generate mutant VVs with enhanced efficiency.

Vaccinia virus (VV) has been widely used in biomedical research and the improvement of human health. This article describes a simple, highly efficient method to edit the VV genome using a CRISPR-Cas9 system.

The CRISPR-associated endonuclease Cas9 can edit particular genomic loci directed by a single guide RNA (gRNA). The CRISPR/Cas9 system has been ...

Retroviral Transduction of Helper T Cells as a Genetic Approach to Study Mechanisms Controlling their Differentiation and Function

Helper T cell development and function must be tightly regulated to induce an appropriate immune response that eliminates specific pathogens yet prevents autoimmunity. Many approaches involving different model organisms have been utilized to understand the mechanisms controlling helper T cell development and function. However, studies using mouse models have proven to be highly informative due to the availability of genetic, cellular, and biochemical systems. One genetic approach in mice used by many labs involves retroviral transduction of primary helper T cells. This is a powerful approach due to its relative ease, making it accessible to almost any laboratory with basic skills in molecular biology and immunology. Therefore, multiple genes in wild type or mutant forms can readily be tested for function in helper T cells to understand their importance and mechanisms of action. We have optimized this approach and describe here the protocols for production of high titer retroviruses, isolation of primary murine helper T cells, and their transduction by retroviruses and differentiation toward the different helper subsets. Finally, the use of this approach is described in uncovering mechanisms utilized by microRNAs (miRNAs) to regulate pathways controlling helper T cell development and function.

Many experimental systems have been utilized to understand the mechanisms regulating T cell development and function in an immune response. Here a genetic approach using retroviral transduction is described, which is economic, time efficient, and most importantly, highly informative in identifying regulatory pathways.

Helper T cell development and function must be tightly regulated to induce an appropriate immune response that eliminates specific pathogens yet prevents ...