This work was supported by National Institutes of Health Grants R01 AI129302 (to S.I.S.) and the Training Program in Pharmacology: From Bench to Bedside at UC Davis (NIH T32 GM099608 to L.S.A). The Molecular and Genomic Imaging (CMGI) at the University of California Davis provided superb technological support.

All mouse studies were reviewed and approved by the Institutional Animal Care and Use Committee at UC Davis and were performed according to the guidelines of the Animal Welfare Act and the Health Research Extension Act. Be sure to use sterile gloves when working with animals.
1. Mouse Source and Housing
<ol>
	<li>Derive LysM-eGFP mice on a C57BL/6J genetic background as described previously12. Derive LysM-EGFP&#215;MyD88-/- mice by crossing LysM-EGFP mice w...

<ol>
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S., Cho, J. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Immunity+against+Staphylococcus+aureus+cutaneous+infections.">Immunity against Staphylococcus aureus cutaneous infections.</a> Nature Reviews Immunology. 11 (8), 505-518 (2011).</li><li>Hasenberg, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Catchup:+a+mouse+model+for+imaging-based+tracking+and+modulation+of+neutrophil+granulocytes.">Catchup: a mouse model for imaging-based tracking and modulation of neutrophil granulocytes.</a> Nature Methods. 12 (5), 445-452 (2015).</li><li>Faust, N., Varas, F., Kelly, L. M., Heck, S., Graf, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Insertion+of+enhanced+green+fluorescent+protein+into+the+lysozyme+gene+creates+mice+with+green+fluorescent+granulocytes+and+macrophages.">Insertion of enhanced green fluorescent protein into the lysozyme gene creates mice with green fluorescent granulocytes and macrophages.</a> Blood. 96 (2), 719-726 (2000).</li><li>Falahee, P. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=&#945;-Toxin+Regulates+Local+Granulocyte+Expansion+from+Hematopoietic+Stem+and+Progenitor+Cells+in+Staphylococcus+aureus-Infected+Wounds.">&#945;-Toxin Regulates Local Granulocyte Expansion from Hematopoietic Stem and Progenitor Cells in Staphylococcus aureus-Infected Wounds.</a> Journal of immunology. 199 (5), 1772-1782 (2017).</li><li>Kim, M. -. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dynamics+of+Neutrophil+Infiltration+during+Cutaneous+Wound+Healing+and+Infection+Using+Fluorescence+Imaging.">Dynamics of Neutrophil Infiltration during Cutaneous Wound Healing and Infection Using Fluorescence Imaging.</a> Journal of Investigative Dermatology. 128 (7), 1812-1820 (2008).</li><li>Liese, J., Rooijakkers, S. H. M., Strijp, J. A. G., Novick, R. P., Dustin, M. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intravital+two-photon+microscopy+of+host-pathogen+interactions+in+a+mouse+model+of+Staphylococcus+aureus+skin+abscess+formation.">Intravital two-photon microscopy of host-pathogen interactions in a mouse model of Staphylococcus aureus skin abscess formation.</a> Cellular Microbiology. 15 (6), 891-909 (2013).</li><li>Bogoslowski, A., Butcher, E. C., Kubes, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophils+recruited+through+high+endothelial+venules+of+the+lymph+nodes+via+PNAd+intercept+disseminating+Staphylococcus+aureus.">Neutrophils recruited through high endothelial venules of the lymph nodes via PNAd intercept disseminating Staphylococcus aureus.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (10), 2449-2454 (2018).</li><li>Takeuchi, O., Hoshino, K., Akira, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cutting+Edge:+TLR2-Deficient+and+MyD88-Deficient+Mice+Are+Highly+Susceptible+to+Staphylococcus+aureus+Infection.">Cutting Edge: TLR2-Deficient and MyD88-Deficient Mice Are Highly Susceptible to Staphylococcus aureus Infection.</a> The Journal of Immunology. 165 (10), 5392-5396 (2000).</li><li>Miller, L. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MyD88+Mediates+Neutrophil+Recruitment+Initiated+by+IL-1R+but+Not+TLR2+Activation+in+Immunity+against+Staphylococcus+aureus.">MyD88 Mediates Neutrophil Recruitment Initiated by IL-1R but Not TLR2 Activation in Immunity against Staphylococcus aureus.</a> Immunity. 24 (1), 79-91 (2006).</li><li>Macedo, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Wound+healing+is+impaired+in+MyD88-deficient+mice:+a+role+for+MyD88+in+the+regulation+of+wound+healing+by+adenosine+A2A+receptors.">Wound healing is impaired in MyD88-deficient mice: a role for MyD88 in the regulation of wound healing by adenosine A2A receptors.</a> The American Journal of Pathology. 171 (6), 1774-1788 (2007).</li><li>Cho, J. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Neutrophil-derived+IL-1&#946;+Is+Sufficient+for+Abscess+Formation+in+Immunity+against+Staphylococcus+aureus+in+Mice.">Neutrophil-derived IL-1&#946; Is Sufficient for Abscess Formation in Immunity against Staphylococcus aureus in Mice.</a> PLoS Pathogens. 8 (11), e1003047 (2012).</li><li>Granick, J. L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Staphylococcus+aureus+recognition+by+hematopoietic+stem+and+progenitor+cells+via+TLR2/MyD88/PGE2+stimulates+granulopoiesis+in+wounds.">Staphylococcus aureus recognition by hematopoietic stem and progenitor cells via TLR2/MyD88/PGE2 stimulates granulopoiesis in wounds.</a> Blood. 122 (10), 1770-1778 (2013).</li><li>Kim, M. 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S. aureus infection models that utilize bioluminescent S. aureus infection in a fluorescent neutrophil reporter mouse in conjunction with advanced techniques of whole animal in vivo optical imaging have advanced our knowledge of the innate immune response to infection. Previous studies using the LysM-EGFP mouse have shown that up to 1 x 107 neutrophils recruit to an S. aureus infected wound over the first 24 h of infection14, and wound-recruited neutrophils ex...

Staphylococcus aureus (S. aureus) accounts for the majority of skin and soft tissue infections (SSTIs) in the United States1. The incidence of methicillin-resistant S. aureus (MRSA) infections has increased steadily over the past two decades2, motivating the study of the mechanisms of persistence and the discovery of new treatment strategies. The standard of care for MRSA infections is systemic antibiotic therapy, but MRSA has become increasingly resistant to antibiotics over time3 and these drugs can diminish the host&#39;s beneficial microbiome, causing negative health effects, especially in children4. Preclinical studies have examined alternative strategies to treat MRSA infections5, but translating these approaches to the clinic has proved challenging due to emergence of virulence factors that thwart host immune responses6. To dissect the host-pathogen dynamics that drive S. aureus SSTIs, we combine noninvasive and longitudinal readouts of the number of neutrophils recruited to the wound bed with kinetic measures of bacterial abundance and wound area.
Neutrophils are the most abundant circulating leukocyte in humans and the first responders to a bacterial infection7. Neutrophils are a necessary component for an effective host response against S. aureus infections due to their bactericidal mechanisms, including production of reactive oxygen species, proteases, antimicrobial peptides and functional responses including phagocytosis and neutrophil extracellular trap production8,9. Human patients with genetic defects in neutrophil function, such as chronic granulomatous disease and Chediak-Higashi syndrome, show an increased susceptibility to S. aureus infection. In addition, patients with genetic (such as congenital neutropenia) and acquired (such as neutropenia seen in chemotherapy patients) defects in neutrophil numbers are also highly susceptible to S. aureus infection10. Given the importance of neutrophils in clearing S. aureus infections, enhancing their immune capacity or tuning their numbers within a S. aureus lesion may prove an effective strategy in resolving infection.
Over the past decade, transgenic mice with fluorescence neutrophil reporters have been developed to study their trafficking11,12. Combining neutrophil reporter mice with whole animal imaging techniques permits spatiotemporal analysis of neutrophils in tissues and organs. When combined with bioluminescent strains of S. aureus, it is possible to track the accumulation of neutrophils in response to S. aureus abundance and persistence in the context of bacterial virulence factors that directly and indirectly perturb neutrophil numbers in affected tissue13,14,15,16.
Mice are less susceptible to S. aureus virulence and immune evasion mechanisms than humans. As such, wild-type mice may not be an ideal animal model to investigate the efficacy of a given therapeutic to treat chronic S. aureus infection. MyD88-deficient mice (i.e., MyD88-/- mice), an immunocompromised mouse strain that lacks functional interleukin-1 receptor (IL-1R) and Toll-like receptor (TLR) signaling, show greater susceptibility to S. aureus infection compared to wild-type mice17 and an impairment in neutrophil trafficking to a site of S. aureus infection in the skin18. Development of a mouse strain that possesses a fluorescent neutrophil reporter in MyD88-/- mice has provided an alternative model for investigating the efficacy of therapies to treat S. aureus infection compared to current neutrophil reporter mice.
In this protocol, we characterize S. aureus infection in the immunocompromised LysM-EGFP&#215;MyD88-/- mice, and compare the time course and resolution of infection with the LysM-EGFP mice. LysM-EGFP&#215;MyD88-/- mice develop a chronic infection that does not resolve, and 75% succumb to infection after 8 days. A significant defect in initial neutrophil recruitment occurs over 72 h of the inflammatory phase of infection, and 50% fewer neutrophils recruit during the latter stage of infection. The increased susceptibility of the LysM-EGFP&#215;MyD88-/- mice makes this particular strain a rigorous preclinical model to evaluate the efficacy of new therapeutic techniques targeting S. aureus infection compared to current models that utilize wild-type mice, especially techniques aiming to boost the innate immune response against infection.

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			<td height="21" style="height:21px;width:336px;">14 mL Polypropylene Round-Bottom Tube</td>
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			<td height="21" style="height:21px;">Bioluminescent S. aureus</td>
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			<td>Becton, Dickson and Company</td>
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			<td>Perkin Elmer</td>
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			<td height="21" style="height:21px;">Living Image Software &#8211; IVIS Spectrum Series</td>
			<td>Perkin Elmer</td>
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			<td height="21" style="height:21px;">LysM-eGFP Mice</td>
			<td>Thomas Graff Albert Einstein College of New York&#160;</td>
			<td>NA</td>
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			<td height="21" style="height:21px;">Microvolume Spectrophotometer</td>
			<td>ThermoFisher Scientific</td>
			<td>ND-2000</td>
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			<td height="21" style="height:21px;">MyD88 KO Mice</td>
			<td>Jackson Labratory</td>
			<td>009088</td>
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			<td height="21" style="height:21px;">Non-woven sponges</td>
			<td>AMD- Ritmed Inc</td>
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			<td height="21" style="height:21px;">Tryptic Soy Broth</td>
			<td>Becton, Dickson and Company</td>
			<td>211825</td>
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a mouse model to assess innate immune response to staphylococcus aureus infection

Staphylococcus aureus (S. aureus)&#160;infections, including methicillin resistant stains, are an enormous burden on the healthcare system. With incidence rates of S. aureus infection climbing annually, there is a demand for additional research in its&#160;pathogenicity. Animal models of infectious disease advance our understanding of the host-pathogen response and lead to the development of effective therapeutics. Neutrophils play a primary role in the innate immune response that controls S. aureus infections by forming an abscess to wall off the infection and facilitate bacterial clearance; the number of neutrophils that infiltrate an S. aureus skin infection often correlates with disease outcome. LysM-EGFP mice, which possess the enhanced green fluorescent protein (EGFP) inserted in the Lysozyme M (LysM) promoter region (expressed primarily by neutrophils), when used in conjunction with in vivo whole animal fluorescence imaging (FLI) provide&#160;a means of quantifying neutrophil emigration noninvasively and longitudinally into wounded skin. When combined with a bioluminescent S. aureus strain and sequential in vivo whole animal bioluminescent imaging (BLI), it is possible to longitudinally monitor both the neutrophil recruitment dynamics and in vivo bacterial burden at the site of infection in anesthetized mice from onset of infection to resolution or death. Mice are more resistant to a number of virulence factors produced by S. aureus that facilitate effective colonization and infection in humans. Immunodeficient mice provide a more sensitive animal model to examine persistent S. aureus infections and the ability of therapeutics to boost innate immune responses. Herein, we characterize responses in LysM-EGFP mice that have been bred to MyD88-deficient mice (LysM-EGFP&#215;MyD88-/- mice) along with wild-type LysM-EGFP mice to investigate S. aureus skin wound infection. Multispectral simultaneous detection enabled study of neutrophil recruitment dynamics by using in vivo FLI, bacterial burden by using in vivo BLI, and wound healing longitudinally and noninvasively over time.

LysM-EGFP&#215;MyD88-/- mice are more susceptible to S. aureus infection than LysM-EGFP mice
The strain of S. aureus used in this study, ALC290618, was constructed with a plasmid that contains the lux construct that produces bioluminescent signals from live and actively metabolizing bacteria. When inoculated into mice, in vivo bioluminescence imaging (BLI) techn...

Watch this Scientific Journal Video about A Mouse Model to Assess Innate Immune Response to Staphylococcus aureus Infection at JoVE.com

A Mouse Model to Assess Innate Immune Response to Staphylococcus aureus Infection

An approach is described for real-time detection of the innate immune response to cutaneous wounding and Staphylococcus aureus infection of mice. By comparing LysM-EGFP mice (which possess fluorescent neutrophils) with a LysM-EGFP crossbred immunodeficient mouse strain, we advance our understanding of infection and the development of approaches to combat infection.

A Mouse Model to Assess Innate Immune Response to Staphylococcus aureus Infection

Staphylococcus aureus (S. aureus)&#160;infections, including methicillin resistant stains, are an enormous burden on the healthcare system. With incidence ...

Techniques that monitor the bacteria burden and a neutrophil respond simultaneously can provide insight into the mechanisms of Staph aureus persistence and the efficacy of treatment strategies. The main advantage of this technique is that multiple parameters can be measured longitudinally in a live host throughout the duration of infection. It is critical to show where to place the wound on a mouse dorsum, how to excise the skin, and how to inoculate the wound with Staph aureus.Begin by thawing the bioluminescence Staph aureus strain of interest from negative 80 degrees Celsius storage on ice. Before streaking the culture on a 5%bovine blood agar plate. For an overnight incubation at 37 degrees Celsius.The next morning, transfer three to four individual colonies from the Staph aureus plate into the tryptic soy broth, or TSB. Supplemented with 10 micrograms per milliliter of chloramphenicol for an overnight shaking incubation at 37 degrees Celsius. The next morning, dilute 120 microliters of culture sample in six milliliters of TSB.With 10 micrograms per milliliter of chloramphenicol, for a two hour incubation at 37 degrees Celsius, and 200 rotations per minute. When the optical density at 600 nanometers reaches 0.5, transfer three milliliters of bacterial suspension into 10 milliliters ice-cold DPBS. After carefully decanting the supernatant, add additional chilled DPBS to the pellet, and vortex the re-suspended bacteria thoroughly.After a second centrifugation, re-suspend the bacterial pellet in 1.5 milliliters of PBS on ice. To verify bacteria concentration, serially dilute 100 microliters of the bacterial suspension by a factor of 1 x 10 to the 4th, and 1 x 10 to the 5th, in fresh PBS. And plate 20 microliters of each dilution on individual agar plates.After an overnight incubation at 37 degrees Celsius, count the number of colony-forming units by gross examination to calculate the bacterial concentration from the previous day. For excisional skin wounding of the recipient animals, confirm a lack of response to toe pinch, before shaving a one by two inch section on the back of the mouse. Gently wipe to remove any stray hairs.And disinfect the exposed skin, with sequential 10%povidone iodine, and 70%ethanol soaked gauze applications. Moving outward from the center of the surgical area, in a spiral pattern. After allowing the skin to dry for about one minute, firmly press a sterile six millimeter punch biopsy at the center of the prepared surgical area.Twist the punch biopsy to create a circular outline on the skin, that fully cuts through the skin tissue, and at least one section of the outline. Taking care to not to cut into the underlying fascia or tissue. Then use sterile scissors, and forceps, to cut through the epidermis and dermis, following the circular pattern imprinted by the punch biopsy.For Staph aureus inoculation, fill a 28 gauge insulin syringe with 50 microliters of the prepared bioluminescent bacterial inoculant. And use a finger to pull the dermis of the wounded animal to the side. Holding the syringe nearly parallel to the tissue, slowly insert the syringe into the tissue until a sudden decrease in resistance is felt.Indicating piercing of the fascia. With the needle placed in the center of the wound, slowly deliver the entire volume of the inoculant. Confirm that the inoculant forms a bubble at the center of the wound, with minimal leakage or dispersion.And remove the syringe slowly from the animal. Then return the animal to it's cage with heat and monitoring until full recovery. After wounding and infection, and daily during the experiment, place the anesthetized mouse in a bioluminescent and florescence imager, with the wound as flat as possible.In the imager software, select luminescence and photograph as the imaging modes. The exposure time should be preset to one minute at small binning, F/Stop 1 for luminescence, F/Stop 8 for photograph, and open for the emission filter. Then click acquire, to record the image.For in vivo fluorescence imaging, select fluorescence, and photograph, as the imaging modes. The exposure time should be preset to one second at small binning, F/Stop 1 for fluorescence, F/Stop 8 for photograph, and Excitation and Emission wavelengths of 465 over 30 nanometers, and 520 over 20 nanometers, with a high lamp intensity, respectively. Then click acquire to record the image.After obtaining both sets of images, return the animal to it's cage, with monitoring, until full recovery. For image analysis, open the image to be quantified, in an appropriate image analysis software program, and place the default circular region of interest over the entire wound area including the surrounding skin. Click measure region of interest, and record the values for the mean flux for the wound, to allow the mean flux of each signal to be plotted versus time.To measure the wound healing, fit a circular region of interest over the wound edge, and measure the area of the wound in centimeters squared, to allow plotting of the fractional change from the baseline versus time. In this representative experiment, conditional EGFP expression myeloid differentiation primary response 88, Or MyD88 knockout mice, demonstrated a greater susceptibility to Staph aureus inoculation, than did non conditional EGFP expressing animals. With an 80%lethality observed during the first eight days of infection.Both strains of mice lost approximately 5%of their body weights immediately following infection. However, the conditional EGFP expressing mice recovered their original weights by day two. While the MyD88 mice did not.Wound closure in the presence of Staph aureus infection was not different between the two strains. However, sterilely wounded MyD88 knockout mice, had a significant defect in wound healing, compared to conditional EGFP expressing animals. Whole animal imaging revealed a higher bacterial burden, as evidenced by an increased bioluminescent signal in the wounds of MyD88 knockout animals, compared to conditional EGFP expressing animals.A 40%decrease in initial neutrophil trafficking to uninfected wounds of MyD88 knockout animals, was also observed compared to conditional EGFP expressing animals. When 1 x 10 to the 7th colony forming units of Staph aureus were introduced immediately after wounding, neutrophil trafficking was significantly attenuated in knockout animals compared to conditional EGFP expressing animals. Before dispensing the bacteria, make sure there are no air bubbles in the syringe, and that the location of the needle is correctly positioned in the center of the wound.Animal tissues can be harvested at end point to measure the expression of proteins of interest and bacterial dissemination from the wound. Staph aureus is infectious to humans. As such, personal protective equipment should be worn when handling the bacteria, and caution should be exercised, when handling a syringe containing the pathogen.This technique has helped explore the use of biological treatments for Staph aureus infections that enhance the hosts innate immune response against infection.

a-mouse-model-to-assess-innate-immune-response-to-staphylococcus

Research

JoVE Journal

Immunology and Infection

10.5K vistas.  University of California Davis. Las técnicas que monitorean la carga bacteriana y un neutrófilo responden simultáneamente pueden proporcionar información sobre los mecanismos de persistencia de Staph aureus y la eficacia de las estrategias de tratamiento. La principal ventaja de esta técnica es que múltiples parámetros se pueden medir longitudinalmente en un huésped vivo durante toda la duración de la infección. Es fundamental mostrar dónde colocar la herida en un dorso de ratón, cómo extirpar la piel y cómo i...