Name: a novel high-throughput ex vivo ovine skin wound model for testing emerging antibiotics
Uploaded: 2022-09-16T13:20:00
Description: Watch this Scientific Journal Video about A Novel High-Throughput Ex Vivo Ovine Skin Wound Model for Testing Emerging Antibiotics at JoVE.com

The authors would like to thank EPSRC (EP/R513313/1) for funding. The authors would like to also thank R.B Elliot and Son Abattoir in Calow, Chesterfield, for providing lambs&#39; heads and for being so accommodating in the early stages of the project, Kasia Emery for her support throughout the development of this protocol, and Fiona Wright from the Department of Infection, Immunity and Cardiovascular Disease at the University of Sheffield for processing the histology samples and being so incredibly helpful throughout this project.

Lambs&#39; heads from the R.B Elliott and Son Abattoir were used as the source of skin samples in this project. All lambs were slaughtered for consumption as food. Instead of discarding the heads, these were repurposed for research. Ethics approval was not required as the tissue was sourced from waste discarded from abattoirs.
1. Sterilization
<ol>
	<li>Disinfect forceps prior to collection of the heads by taking clean forceps and performing dry heat sterilization in an oven...

<ol>
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W., Vowden, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Costs+and+outcomes+in+evaluating+management+of+unhealed+surgical+wounds+in+the+community+in+clinical+practice+in+the+UK:+A+cohort+study.">Costs and outcomes in evaluating management of unhealed surgical wounds in the community in clinical practice in the UK: A cohort study.</a> BMJ Open. 8 (12), 022591 (2018).</li><li>Sen, C. K., 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=Human+skin+wounds:+A+major+and+snowballing+threat+to+public+health+and+the+economy.">Human skin wounds: A major and snowballing threat to public health and the economy.</a> Wound Repair and Regeneration. 17 (6), 763-771 (2009).</li><li>Wilcox, M. H., Dryden, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Update+on+the+epidemiology+of+healthcare-acquired+bacterial+infections:+Focus+on+complicated+skin+and+skin+structure+infections.">Update on the epidemiology of healthcare-acquired bacterial infections: Focus on complicated skin and skin structure infections.</a> Journal of Antimicrobial Chemotherapy. 76, (2021).</li><li>Han, G., Ceilley, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+wound+healing:+A+review+of+current+management+and+treatments.">Chronic wound healing: A review of current management and treatments.</a> Advances in Therapy. 34 (3), 599-610 (2017).</li><li>Percival, S. L., Hill, K. E., Malic, S., Thomas, D. W., Williams, D. 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G., 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=Evaluation+of+gallium+citrate+formulations+against+a+multidrug-resistant+strain+of+Klebsiella+pneumoniae+in+a+murine+wound+model+of+infection.">Evaluation of gallium citrate formulations against a multidrug-resistant strain of Klebsiella pneumoniae in a murine wound model of infection.</a> Antimicrobial Agents and Chemotherapy. 59 (10), 6484-6493 (2015).</li><li>Maboni, G., 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=A+novel+3D+skin+explant+model+to+study+anaerobic+bacterial+infection.">A novel 3D skin explant model to study anaerobic bacterial infection.</a> Frontiers in Cellular and Infection Microbiology. 7, 404 (2017).</li><li>Macneil, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Progress+and+opportunities+for+tissue-engineered+skin.">Progress and opportunities for tissue-engineered skin.</a> Nature. 445 (7130), 874-880 (2007).</li><li>Theuretzbacher, U., Outterson, K., Engel, A., Karl&#233;n, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+global+preclinical+antibacterial+pipeline.">The global preclinical antibacterial pipeline.</a> Nature Reviews Microbiology. 18 (5), 275-285 (2019).</li><li>Miethke, M., 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=Towards+the+sustainable+discovery+and+development+of+new+antibiotics.">Towards the sustainable discovery and development of new antibiotics.</a> Nature Reviews Chemistry. 5 (10), 726-749 (2021).</li><li>Guedes, G. M. M., 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=Ex+situ+model+of+biofilm-associated+wounds:+Providing+a+host-like+environment+for+the+study+of+Staphylococcus+aureus+and+Pseudomonas+aeruginosa+biofilms.">Ex situ model of biofilm-associated wounds: Providing a host-like environment for the study of Staphylococcus aureus and Pseudomonas aeruginosa biofilms.</a> Journal of Applied Microbiology. 131 (3), 1487-1497 (2021).</li><li>Johnson, C. J., 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=Augmenting+the+activity+of+chlorhexidine+for+decolonization+of+Candida+auris+from+porcine+skin.">Augmenting the activity of chlorhexidine for decolonization of Candida auris from porcine skin.</a> Journal of Fungi. 7 (10), 804 (2021).</li><li>Horton, M. V., 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=Candida+auris+Forms+High-Burden+Biofilms+in+Skin+Niche+Conditions+and+on+Porcine+Skin.">Candida auris Forms High-Burden Biofilms in Skin Niche Conditions and on Porcine Skin.</a> mSphere. 5 (1), 00910-00919 (2020).</li><li>Ashrafi, M., 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=Validation+of+biofilm+formation+on+human+skin+wound+models+and+demonstration+of+clinically+translatable+bacteria-specific+volatile+signatures.">Validation of biofilm formation on human skin wound models and demonstration of clinically translatable bacteria-specific volatile signatures.</a> Scientific Reports. 8, 1-16 (2018).</li><li>Brackman, G., Coenye, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vitro+and+in+vivo+biofilm+wound+models+and+their+application.">In vitro and in vivo biofilm wound models and their application.</a> Advances in Experimental Medicine and Biology. 897, 15-32 (2016).</li><li>Rumbaugh, K. P., Carty, N. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+Vivo+Models+of+Biofilm+Infection.">In Vivo Models of Biofilm Infection.</a> Biofilm Infections. , 267-290 (2011).</li><li>Boase, S., Valentine, R., Singhal, D., Tan, L. W., Wormald, P. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+sheep+model+to+investigate+the+role+of+fungal+biofilms+in+sinusitis:+Fungal+and+bacterial+synergy.">A sheep model to investigate the role of fungal biofilms in sinusitis: Fungal and bacterial synergy.</a> International Forum of Allergy &amp; Rhinology. 1 (5), 340-347 (2011).</li><li>Williams, D. 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=Experimental+model+of+biofilm+implant-related+osteomyelitis+to+test+combination+biomaterials+using+biofilms+as+initial+inocula.">Experimental model of biofilm implant-related osteomyelitis to test combination biomaterials using biofilms as initial inocula.</a> Journal of Biomedical Materials Research. Part A. 100 (7), 1888-1900 (2012).</li><li>Scheerlinck, J. P. Y., Snibson, K. J., Bowles, V. M., Sutton, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Biomedical+applications+of+sheep+models:+From+asthma+to+vaccines.">Biomedical applications of sheep models: From asthma to vaccines.</a> Trends in Biotechnology. 26 (5), 259-266 (2008).</li><li>Metcalfe, A. D., Ferguson, M. W. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tissue+engineering+of+replacement+skin:+The+crossroads+of+biomaterials,+wound+healing,+embryonic+development,+stem+cells+and+regeneration.">Tissue engineering of replacement skin: The crossroads of biomaterials, wound healing, embryonic development, stem cells and regeneration.</a> Journal of the Royal Society Interface. 4 (14), 413-417 (2007).</li><li>Kazemi-Darabadi, S., Sarrafzadeh-Rezaei, F., Farshid, A. A., Dalir-Naghadeh, B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Allogenous+skin+fibroblast+transplantation+enhances+excisional+wound+healing+following+alloxan+diabetes+in+sheep,+a+randomized+controlled+trial.">Allogenous skin fibroblast transplantation enhances excisional wound healing following alloxan diabetes in sheep, a randomized controlled trial.</a> International Journal of Surgery. 12 (8), 751-756 (2014).</li><li>Martinello, T., 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=Allogeneic+mesenchymal+stem+cells+improve+the+wound+healing+process+of+sheep+skin.">Allogeneic mesenchymal stem cells improve the wound healing process of sheep skin.</a> BMC Veterinary Research. 14 (1), 1-9 (2018).</li><li>Roberts, C. D., Windsor, P. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Innovative+pain+management+solutions+in+animals+may+provide+improved+wound+pain+reduction+during+debridement+in+humans:+An+opinion+informed+by+veterinary+literature.">Innovative pain management solutions in animals may provide improved wound pain reduction during debridement in humans: An opinion informed by veterinary literature.</a> International Wound Journal. 16 (4), 968 (2019).</li><li>Mazzone, 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=Bioengineering+and+in+utero+transplantation+of+fetal+skin+in+the+sheep+model:+A+crucial+step+towards+clinical+application+in+human+fetal+spina+bifida+repair.">Bioengineering and in utero transplantation of fetal skin in the sheep model: A crucial step towards clinical application in human fetal spina bifida repair.</a> Journal of Tissue Engineering and Regenerative Medicine. 14 (1), 58-65 (2020).</li><li>Olkowska, E., Gr&#382;ini&#263;, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Skin+models+for+dermal+exposure+assessment+of+phthalates.">Skin models for dermal exposure assessment of phthalates.</a> Chemosphere. 295, 133909 (2022).</li><li>Couto, N., 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=Label-free+quantitative+proteomics+and+substrate-based+mass+spectrometry+imaging+of+xenobiotic+metabolizing+enzymes+in+ex+vivo+human+skin+and+a+human+living+skin+equivalent+model.">Label-free quantitative proteomics and substrate-based mass spectrometry imaging of xenobiotic metabolizing enzymes in ex vivo human skin and a human living skin equivalent model.</a> Drug Metabolism and Disposition. 49 (1), 39-52 (2021).</li></ol>

The development of antimicrobials is an important but expensive venture that is estimated to cost around $1 billion and take around 15 years to complete. Over 90% of antimicrobial drug discovery and preclinical studies of antimicrobial drug efficacy are carried out by academic researchers and small to medium companies with typically less than 50 employees22. These teams are very financially constrained, which makes the failure of lead molecules in later stages of translational research calamitous....

Skin infections are an important global issue, with large economic costs to healthcare providers around the world. The development of multidrug resistance and biofilm formation by pathogens plays a key role in the prevalence of non-healing wounds1,2,3,4. As a result of this, skin and soft tissue infections are one of the more common reasons for extended hospitalization and subsequent readmission5. Delays in wound healing are costly for both the patient and healthcare providers, with some estimates suggesting around 6.5 million patients are affected annually in the US. In the UK, skin infections and associated complications result in approximately 75,000 deaths annually2,4,6.
Staphylococcus aureus (S. aureus) is a formidable wound pathogen frequently isolated from patient wounds2,7. The rate of emergence of multidrug resistance increased drastically in the 2000s. During this time, around 60% of acute bacterial skin and skin structure infections were culture positive for methicillin-resistant S. aureus1. The increasing number of multidrug-resistant strains among Staphylococci, and indeed other pathogens, within the last 2 decades indicates an urgent need for the rapid development of antibiotics with new modes of action that can overcome resistance.
However, since the early 2000s, antibiotic discovery programs have been dominated by longer developmental times and low success rates, with only 17% of novel antibiotics entering clinical trials in the US achieving market approval8. This suggests a disparity between results from in vitro testing of emerging antibiotics and their clinical outcomes. It can be contended that this disparity is largely due to differences in bacterial physiology during infections in vivo and during conventional microbiological methods when testing the efficacy of antibiotics in the in vitro preclinical stages. Therefore, novel laboratory methods that are more representative of bacterial physiology during infection are needed to improve the success rates in antibiotic discovery programs.
Current methods for studying skin infections include studies in live animals (e.g., mice), ex vivo skin models (e.g., porcine), and 3D tissue-engineered skin models (e.g., human)9,10,11,12. Studies in live animals are strictly regulated and have relatively low throughput. In animal models, wounding and infection cause significant distress to the animals and raise ethical concerns. Human skin models, ex vivo or tissue-engineered, require ethical approval, compliance with local and global legislation (the Human Tissue Act, the Declaration of Helsinki), and there is difficulty in acquiring tissues, with some requests taking years to fulfil13,14. Both model types are labor intensive and require significant expertise to ensure experimental success. Some current ex vivo skin infection models require pre-inoculated discs and additives for the wound bed to enable infection; although these models are incredibly useful, there are limitations in the infection process as additives limit the utilization of the wound bed as a nutrient source10,15,16,17. The model described in this study uses no additives to the wound bed, which ensures that the pathology of infection and viable cell counts are a result of direct utilization of the wound bed as the only nutrient source.
Given the need for new laboratory methods, a novel high-throughput ex vivo ovine model of skin infections for use in evaluating the efficacy of emerging antibiotics has been developed. Skin infection studies face many challenges-high costs, ethical concerns, and models that do not show a full picture20,21. Ex vivo models and 3D explant models allow for better visualization of the disease process and the impact treatments can have from a more clinically relevant model. Here, the setup of a novel ovine skin model is described, which&#160;is simple, reproducible, and clinically relevant and has high throughput. Ovine skin was chosen as sheep are one of the large mammals commonly used to model responses to infections in vivo. Moreover, they are readily available from abattoirs, ensuring a steady supply of skin for research, and their carcasses are not scalded, ensuring good tissue quality. This study used S. aureus as the exemplar pathogen; however, the model works well with other microorganisms.

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	<tbody>
		<tr>
			<td>24 Well Companion Plate</td>
			<td>SLS&#160;</td>
			<td>353504</td>
			<td></td>
		</tr>
		<tr>
			<td>4 mm Biopsy Punch</td>
			<td>Williams Medical</td>
			<td>D7484</td>
			<td></td>
		</tr>
		<tr>
			<td>50 ml centrifuge tubes</td>
			<td>Fisher Scientific&#160;</td>
			<td>10788561</td>
			<td></td>
		</tr>
		<tr>
			<td>8 mm Biopsy Punch</td>
			<td>Williams Medical</td>
			<td>D7488</td>
			<td></td>
		</tr>
		<tr>
			<td>Amphotericin B solution, sterile</td>
			<td>Sigma&#160;</td>
			<td>A2942</td>
			<td></td>
		</tr>
		<tr>
			<td>Colour Pro Style Cordless Hair Clipper</td>
			<td>Wahl</td>
			<td>9639-2117X</td>
			<td>Hair Clippers</td>
		</tr>
		<tr>
			<td>Dual Oven Incubator</td>
			<td>SLS</td>
			<td>OVe1020</td>
			<td>Sterilising oven</td>
		</tr>
		<tr>
			<td>Epidermal growth factor&#160;</td>
			<td>SLS</td>
			<td>E5036-200UG</td>
			<td></td>
		</tr>
		<tr>
			<td>Ethanol</td>
			<td>Honeywell</td>
			<td>458600-2.5L</td>
			<td></td>
		</tr>
		<tr>
			<td>F12 HAM</td>
			<td>Sigma</td>
			<td>N4888</td>
			<td></td>
		</tr>
		<tr>
			<td>Foetal bovine serum&#160;</td>
			<td>Labtech International</td>
			<td>CA-115/500</td>
			<td></td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>Fisher Scientific</td>
			<td>15307805</td>
			<td></td>
		</tr>
		<tr>
			<td>Hair Removal Cream</td>
			<td>Veet</td>
			<td>Not applicable</td>
			<td></td>
		</tr>
		<tr>
			<td>Heracell VIOS 160i</td>
			<td>Thermo Scientific</td>
			<td>15373212&#160;</td>
			<td>Tissue culture incubator</td>
		</tr>
		<tr>
			<td>Heraeus Megafuge 16R</td>
			<td>VWR</td>
			<td>521-2242</td>
			<td>Centrifuge</td>
		</tr>
		<tr>
			<td>Homogenizer 220, Handheld</td>
			<td>Fisher Scientific</td>
			<td>15575809</td>
			<td></td>
		</tr>
		<tr>
			<td>Homogenizer 220, plastic blending cones</td>
			<td>Fisher Scientific&#160;</td>
			<td>15585819</td>
			<td></td>
		</tr>
		<tr>
			<td>Insert Individual 24 well 0.4um membrane</td>
			<td>VWR International</td>
			<td>353095</td>
			<td></td>
		</tr>
		<tr>
			<td>Insulin, recombinant Human</td>
			<td>SLS</td>
			<td>91077C-1G</td>
			<td></td>
		</tr>
		<tr>
			<td>Medium 199 (MK media)</td>
			<td>Sigma</td>
			<td>M0393</td>
			<td></td>
		</tr>
		<tr>
			<td>Microplate, cell culture Costar 96 well</td>
			<td>Fisher Scientific</td>
			<td>10687551</td>
			<td></td>
		</tr>
		<tr>
			<td>Multitron</td>
			<td>Infors</td>
			<td>Not applicable</td>
			<td>Bacterial incubator</td>
		</tr>
		<tr>
			<td>PBS tablets</td>
			<td>Sigma&#160;</td>
			<td>P4417-100TAB</td>
			<td></td>
		</tr>
		<tr>
			<td>Penicillin-Streptomycin</td>
			<td>SLS&#160;</td>
			<td>P0781</td>
			<td></td>
		</tr>
		<tr>
			<td>Plate seals</td>
			<td>Fisher Scientific</td>
			<td>ESI-B-100</td>
			<td></td>
		</tr>
		<tr>
			<td>Safe 2020</td>
			<td>Fisher Scientific</td>
			<td>1284804</td>
			<td>Class II microbiology safety cabinet</td>
		</tr>
		<tr>
			<td>Scalpel blade number 15</td>
			<td>Fisher Scientific</td>
			<td>O305</td>
			<td></td>
		</tr>
		<tr>
			<td>Scalpel Swann Morton</td>
			<td>Fisher Scientific</td>
			<td>11849002</td>
			<td></td>
		</tr>
		<tr>
			<td>Sodium bicarbonate</td>
			<td>Sigma</td>
			<td>S5761-1KG</td>
			<td></td>
		</tr>
		<tr>
			<td>Toothed Allis Tissue Forceps</td>
			<td>Rocialle</td>
			<td>RSPU500-322</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptic Soy Agar</td>
			<td>Merck Life Science UK Limited</td>
			<td>14432-500G-F</td>
			<td></td>
		</tr>
		<tr>
			<td>Tryptic Soy Broth</td>
			<td>Merck Life Science UK Limited</td>
			<td>41298-500G-F</td>
			<td></td>
		</tr>
		<tr>
			<td>Vimoba Tablets</td>
			<td>Quip Labs</td>
			<td>VMTAB75BX</td>
			<td></td>
		</tr>
	</tbody>
</table>

a novel high-throughput ex vivo ovine skin wound model for testing emerging antibiotics

The development of antimicrobials is an expensive process with increasingly low success rates, which makes further investment in antimicrobial discovery research less attractive. Antimicrobial drug discovery and subsequent commercialization can be made more lucrative if a fail-fast-and-fail-cheap approach can be implemented within the lead optimization stages where researchers have greater control over drug design and formulation. In this article, the setup of an ex vivo ovine wounded skin model infected with Staphylococcus aureus&#160;is described, which is simple, cost-effective, high throughput, and reproducible. The bacterial physiology in the model mimics that during infection as bacterial proliferation is dependent on the pathogen&#39;s ability to damage the tissue. The establishment of wound infection is verified by an increase in viable bacterial counts compared to the inoculum. This model can be used as a platform to test the efficacy of emerging antimicrobials in the lead optimization stage. It can be contended that the availability of this model will provide researchers developing antimicrobials with a fail-fast-and-fail-cheap model, which will help increase success rates in subsequent animal trials. The model will also facilitate the reduction and refinement of animal use for research and ultimately enable faster and more cost-effective translation of novel antimicrobials for skin and soft tissue infections to the clinic.

The identification of a route to sterilize the skin before setting up the wound infection model was challenging. The challenge lay in sterilizing the skin without damaging the different skin layers, which may then go on to have unintended consequences in the outcome of infection. To identify an appropriate sterilization regime, different treatments were tried for varying lengths of time, as outlined in Table 1. Contamination was recorded as the development of turbidity after 48 h in the MK medium used to...

Watch this Scientific Journal Video about A Novel High-Throughput Ex Vivo Ovine Skin Wound Model for Testing Emerging Antibiotics at JoVE.com

A Novel High-Throughput Ex Vivo Ovine Skin Wound Model for Testing Emerging Antibiotics

The protocol describes a step-by-step method to set up an ex vivo ovine wounded skin model infected with Staphylococcus aureus. This high-throughput model better simulates infections in vivo compared with conventional microbiology techniques and presents researchers with a physiologically relevant platform to test the efficacy of emerging antimicrobials.

A Novel High-Throughput Ex Vivo Ovine Skin Wound Model for Testing Emerging Antibiotics

The development of antimicrobials is an expensive process with increasingly low success rates, which makes further investment in antimicrobial discovery ...

This model will allow the researchers at the critical preclinical stages to more accurately determine the antimicrobial efficacy of novel formulations, and gives researchers greater control over drug design and formulation. This model enables rapid reproducible results in a representative wound environment. It reduces the need for purpose-bred animals, and facilitates the faster translation of topical antimicrobials for wound infections to the clinic.The main challenges are contamination and dexterity. A strict aseptic technique and patience with tissue processing are essential;precise and purposeful flap removal is needed for the success of this method. Begin with the disinfection of forceps by exposing them to dry heat sterilization at 200 degrees Celsius for one hour.Autoclave all glassware at 121 degrees Celsius for 15 minutes before use. Disinfect the forehead section of the lamp by pouring approximately 100 milliliters of 200 PPM chlorine dioxide solution onto the sample area. Shave the forehead section using electric clippers, followed by a wash with 200 milliliters of 200 PPM chlorine dioxide solution.Wipe the area using ethanol and a blue roll, and cover the sample area with hair removal cream. After 35 minutes, gently scrape off the hair removal cream using a scraping tool and assess the sample area. Repeat the hair removal process if a significant amount of hair remains.Rinse the clean sample area with 200 milliliters of chlorine dioxide solution followed by ethanol and a blue roll. Use a sterile eight-millimeter biopsy punch to cut out an eight-millimeter skin sample from the prepared area. Then remove the sample using sterile forceps and number 15 blade scalpel, ensuring that all cutaneous fat is removed.Place the samples in a sterile 0.5 liter jar filled with sterile PBS. Then transfer them to sterile 50-milliliter tubes filled with 50 milliliters of 200 PPM chlorine dioxide solution. Invert the tube twice and leave it to sterilize for 30 minutes.Transfer the samples to a 50-milliliter tube filled with 40 milliliters of sterile PBS. After the PBS wash, place each skin sample in a separate well of a 24-well plate. Add 350 microliters of the pre-warmed medium in a well, while maintaining the sample at the air-liquid interface.Seal the 24-well plates with a gas permeable plate seal before placing the plate for incubation in a humidified tissue incubator at 5%carbon dioxide and 37 degrees Celsius for 24 hours. After incubation, remove the culture medium and rinse the samples in 500 microliters of sterile PBS. Remove the residual antibiotics from the sample by treating them with antibiotic-free media at 5%carbon dioxide and 37 degrees Celsius for 24 hours.If turbidity or fungal infection develops in the antibiotic free media, discard the sample. Next, prepare a 50-milliliter tube with 10 milliliters of sterile Tryptic Soy Broth. Then transfer several Staphylococcus aureus colonies from a fresh agar plate of S.aureus to the broth, and incubate the tube at 37 degrees Celsius and 150 RPM for 18 hours.After centrifuging the tubes at 4, 000 G for three minutes, remove the supernatant and resuspend the cell pellet in 10 milliliters of sterile PBS. Repeat the PBS wash twice before adjusting the inoculum to 0.6 optical density at 600 nanometer wavelengths using sterile PBS. Confirm the inoculum load by a manual viable plate count.To infect the skin sample, prepare a fresh 24-well plate with 400 microliters of pre-warmed antibiotic free media, and add the 24 well inserts using sterile forceps. Remove the media from the skin samples. Wash them with 500 microliters of sterile PBS and remove the wash.Use sterile forceps to gently hold the sample to the bottom of the well. Use a four-millimeter punch biopsy to pierce through the skin sample to a rough depth of one to two millimeters and make a central wound flap. Then use a number 15 blade scalpel and sterile-toothed Allis tissue forceps to remove the top layer of the wound flap.Once all the samples have been wounded, transfer them to the 24 well inserts using sterile forceps. Pipette 15 microliters of the bacterial inoculum into the wound bed before incubating for 24 hours at 37 degrees Celsius in a humidified tissue incubator. For longer incubation periods, remove the media, replace it with fresh media every 24 hours, and incubate the plates under the same conditions.To determine the bacterial load, remove the media from the bottom of the wells. And using sterile forceps, transfer each sample into a separate 50-milliliter tube filled with one milliliter of sterile PBS. Then detach the bacteria from the surface of the wound bed by homogenizing the sample surface with a fine-tipped homogenizer.Ensure that the wound bed is in direct contact with the tip of the homogenizer. Once all the samples are processed, vortex each sample before transferring 20 microliters of homogenate into the corresponding well of a 96-well plate containing 180 microliters of sterile PBS. Serially dilute each sample homogenate to 1 times 10 to the negative 7, and pipette 10 microliters of the diluted homogenate onto a Tryptic Soy Agar plate in triplicate.Incubate the Tryptic Soy Agar plate at 37 degrees Celsius, and after 18 hours, count the number of colonies to determine the colony forming units or CFU for each sample. An appropriate skin sterilization regime was identified using different treatments for varying lengths of time. Tissue integrity was monitored by histology, followed by staining with hematoxylin and eosin immediately after the treatment.A 30-minute treatment with chlorine dioxide was the most effective treatment, with reproducible sterilizing the skin tissue while preserving tissue integrity. A white film in the wound bed was evident on the tissue 48 hours after infection. Although the scratch model harbored a higher average number of CFUs after 24 hours, the flap removal wounding technique produced more consistent results.After 48 hours, approximately 100 times more bacterial CFUs were recovered from the wounded tissue compared to the inoculum, indicating a successful infection. Gram-stained histology sections of the infected tissue indicated the presence of S.aureus cells in the wound bed, which was absent in the sections of uninfected tissue. Following this procedure, one can perform immunohistochemistry to study tissue response, modified gram stain to visualize the bacterial localization, and viable plate counts after antimicrobial exposure to test antimicrobial efficacy.For the researchers developing novel antimicrobials, this model will provide greater control of lead optimization, reduce reliance on expensive and tightly regulated animal trials, and enable the rapid translation of antimicrobials to the clinic.

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Research

JoVE Journal

Immunology and Infection

A 96 Well Microtiter Plate-based Method for Monitoring Formation and Antifungal Susceptibility Testing of Candida albicans Biofilms

Candida albicans remains the most frequent cause of fungal infections in an expanding population of compromised patients and candidiasis is now the third most common infection in US hospitals. Different manifestations of candidiasis are associated with biofilm formation, both on host tissues and/or medical devices (i.e. catheters). Biofilm formation carries negative clinical implications, as cells within the biofilms are protected from host immune responses and from the action of antifungals. We have developed a simple, fast and robust in vitro model for the formation of C. albicans biofilms using 96 well microtiter-plates, which can also be used for biofilm antifungal susceptibility testing. The readout of this assay is colorimetric, based on the reduction of XTT (a tetrazolium salt) by metabolically active fungal biofilm cells. A typical experiment takes approximately 24 h for biofilm formation, with an additional 24 h for antifungal susceptibility testing. Because of its simplicity and the use of commonly available laboratory materials and equipment, this technique democratizes biofilm research and represents an important step towards the standardization of antifungal susceptibility testing of fungal biofilms.

A 96 Well Microtiter Plate-based Method for Monitoring Formation and Antifungal Susceptibility Testing of Candida albicans Biofilms

We describe a simple, rapid and robust method for the formation of Candida albicans biofilms using 96 well microtiter plates and its utility in antifungal susceptibility testing of cells within biofilms.

Candida albicans remains the most frequent cause of fungal infections in an expanding population of compromised patients and candidiasis is now the third ...

Isolation of Brain and Spinal Cord Mononuclear Cells Using Percoll Gradients

Isolation of immune cells that infiltrate the central nervous system (CNS) during infection, trauma, autoimmunity or neurodegeneration, is often required to define their phenotype and effector functions. Histochemical approaches are instrumental to determine the location of the infiltrating cells and to analyze the associated CNS pathology. However, in-situ histochemistry and immunofluorescent staining techniques are limited by the number of antibodies that can be used at a single time to characterize immune cell subtypes in a particular tissue. Therefore, histological approaches in conjunction with immune-phenotyping by flow cytometry are critical to fully characterize the composition of local CNS infiltration. This protocol is based on the separation of CNS cellular suspensions over discontinous percoll gradients. The current article describes a rapid protocol to efficiently isolate mononuclear cells from brain and spinal cord tissues that can be effectively utilized for identification of various immune cell populations in a single sample by flow cytometry.

The current article describes a rapid protocol to efficiently isolate mononuclear cells from brain and spinal cord tissues that can be effectively utilized for flow cytometric analyses.

Isolation of immune cells that infiltrate the central nervous system (CNS) during infection, trauma, autoimmunity or neurodegeneration, is often required ...

High-throughput Detection Method for Influenza Virus

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, precise diagnosis of the infecting strain and rapid high-throughput screening of vast numbers of clinical samples is paramount to control the spread of pandemic infections. Current clinical diagnoses of influenza infections are based on serologic testing, polymerase chain reaction, direct specimen immunofluorescence and cell culture 1,2.
Here, we report the development of a novel diagnostic technique used to detect live influenza viruses. We used the mouse-adapted human A/PR/8/34 (PR8, H1N1) virus 3 to test the efficacy of this technique using MDCK cells 4. MDCK cells (104 or 5 x 103 per well) were cultured in 96- or 384-well plates, infected with PR8 and viral proteins were detected using anti-M2 followed by an IR dye-conjugated secondary antibody. M2 5 and hemagglutinin 1 are two major marker proteins used in many different diagnostic assays. Employing IR-dye-conjugated secondary antibodies minimized the autofluorescence associated with other fluorescent dyes. The use of anti-M2 antibody allowed us to use the antigen-specific fluorescence intensity as a direct metric of viral quantity. To enumerate the fluorescence intensity, we used the LI-COR Odyssey-based IR scanner. This system uses two channel laser-based IR detections to identify fluorophores and differentiate them from background noise. The first channel excites at 680 nm and emits at 700 nm to help quantify the background. The second channel detects fluorophores that excite at 780 nm and emit at 800 nm. Scanning of PR8-infected MDCK cells in the IR scanner indicated a viral titer-dependent bright fluorescence. A positive correlation of fluorescence intensity to virus titer starting from 102-105 PFU could be consistently observed. Minimal but detectable positivity consistently seen with 102-103 PFU PR8 viral titers demonstrated the high sensitivity of the near-IR dyes. The signal-to-noise ratio was determined by comparing the mock-infected or isotype antibody-treated MDCK cells.
Using the fluorescence intensities from 96- or 384-well plate formats, we constructed standard titration curves. In these calculations, the first variable is the viral titer while the second variable is the fluorescence intensity. Therefore, we used the exponential distribution to generate a curve-fit to determine the polynomial relationship between the viral titers and fluorescence intensities. Collectively, we conclude that IR dye-based protein detection system can help diagnose infecting viral strains and precisely enumerate the titer of the infecting pathogens.

This method describes the use of Infrared dye based imaging system for detection of H1N1 in bronchioalveolar lavage (BAL) fluid of infected mice at a high sensitivity. This methodology can be performed in a 96- or 384-well plate, requires &lt;10 &mu;l volume of test material and has the potential for concurrent screening of multiple pathogens.

Influenza virus is a respiratory pathogen that causes a high degree of morbidity and mortality every year in multiple parts of the world. Therefore, ...

Lymphocyte Isolation from Human Skin for Phenotypic Analysis and Ex Vivo Cell Culture

Human skin has an important barrier function and contains various immune cells that contribute to tissue homeostasis and protection from pathogens. As the skin is relatively easy to access, it provides an ideal platform to study peripheral immune regulatory mechanisms. Immune resident cells in healthy skin conduct immunosurveillance, but also play an important role in the development of inflammatory skin disorders, such as psoriasis. Despite emerging insights, our understanding of the biology underlying various inflammatory skin diseases is still limited. There is a need for good quality (single) cell populations isolated from biopsied skin samples. So far, isolation procedures have been seriously hampered by a lack of obtaining a sufficient number of viable cells. Isolation and subsequent analysis have also been affected by the loss of immune cell lineage markers, due to the mechanical and chemical stress caused by the current dissociation procedures to obtain single cell suspension. Here, we describe a modified method to isolate T cells from both healthy and involved psoriatic human skin by combining mechanical skin dissociation using an automated tissue dissociator and collagenase treatment. This methodology preserves expression of most immune lineage markers such as CD4, CD8, Foxp3 and CD11c upon the preparation of single cell suspensions. Examples of successful CD4+ T cell isolation and subsequent phenotypic and functional analysis are shown.

Lymphocyte Isolation from Human Skin for Phenotypic Analysis and Ex Vivo Cell Culture

We describe a protocol to efficiently isolate skin resident T cells from human skin biopsies. This protocol yields sufficient numbers of viable human skin resident lymphocytes for flow cytometric analysis and ex vivo culture.

Human skin has an important barrier function and contains various immune cells that contribute to tissue homeostasis and protection from pathogens. As the ...

High Throughput, Real-time, Dual-readout Testing of Intracellular Antimicrobial Activity and Eukaryotic Cell Cytotoxicity

Traditional measures of intracellular antimicrobial activity and eukaryotic cell cytotoxicity rely on endpoint assays. Such endpoint assays require several additional experimental steps prior to readout, such as cell lysis, colony forming unit determination, or reagent addition. When performing thousands of assays, for example, during high-throughput screening, the downstream effort required for these types of assays is considerable. Therefore, to facilitate high-throughput antimicrobial discovery, we developed a real-time assay to simultaneously identify inhibitors of intracellular bacterial growth and assess eukaryotic cell cytotoxicity. Specifically, real-time intracellular bacterial growth detection was enabled by marking bacterial screening strains with either a bacterial lux operon (1st generation assay) or fluorescent protein reporters (2nd generation, orthogonal assay). A non-toxic, cell membrane-impermeant, nucleic acid-binding dye was also added during initial infection of macrophages. These dyes are excluded from viable cells. However, non-viable host cells lose membrane integrity permitting entry and fluorescent labeling of nuclear DNA (deoxyribonucleic acid). Notably, DNA binding is associated with a large increase in fluorescent quantum yield that provides a solution-based readout of host cell death. We have used this combined assay to perform a high-throughput screen in microplate format, and to assess intracellular growth and cytotoxicity by microscopy. Notably, antimicrobials may demonstrate synergy in which the combined effect of two or more antimicrobials when applied together is greater than when applied separately. Testing for in vitro synergy against intracellular pathogens is normally a prodigious task as combinatorial permutations of antibiotics at different concentrations must be assessed. However, we found that our real-time assay combined with automated, digital dispensing technology permitted facile synergy testing. Using these approaches, we were able to systematically survey action of a large number of antimicrobials alone and in combination against the intracellular pathogen, Legionella pneumophila.

A high throughput, real-time assay was developed to simultaneously identify (1) eukaryotic cell-penetrant antimicrobials targeting an intracellular bacterial pathogen, and (2) assess eukaryotic cell cytotoxicity. A variation on the same technology was thereafter combined with digital dispensing technology to enable facile, high-resolution, dose-response, and two- and three-dimensional synergy studies.

Traditional measures of intracellular antimicrobial activity and eukaryotic cell cytotoxicity rely on endpoint assays. Such endpoint assays require ...

A Novel In Vitro Wound Healing Assay to Evaluate Cell Migration

The aim of this work is to show a novel method to evaluate the ability of some immunomodulatory molecules, such as antimicrobial peptides (AMPs), to stimulate cell migration. Importantly, cell migration is a rate-limiting event during the wound-healing process to re-establish the integrity and normal function of tissue layers after injury. The advantage of this method over the classical assay, which is based on a manually made scratch in a cell monolayer, is the usage of special silicone culture inserts providing two compartments to create a cell-free pseudo-wound field with a well-defined width (500 &#956;m). In addition, due to an automated image analysis platform, it is possible to rapidly obtain quantitative data on the speed of wound closure and cell migration. More precisely, the effect of two frog-skin AMPs on the migration of bronchial epithelial cells will be shown. Furthermore, pretreatment of these cells with specific inhibitors will provide information on the molecular mechanisms underlying such events.

A Novel In Vitro Wound Healing Assay to Evaluate Cell Migration

Here, we present a protocol to evaluate the effect of peptides on the migration of bronchial epithelial cells. This method allows for the rapid and highly reproducible obtainment of quantitative data on the speed of cell migration and wound closure.

The aim of this work is to show a novel method to evaluate the ability of some immunomodulatory molecules, such as antimicrobial peptides (AMPs), to ...

In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model

The generation of reactive oxygen species (ROS) is a hallmark of inflammatory processes, but in excess, oxidative stress is widely implicated in various pathologies such as cancer, atherosclerosis and diabetes. We have previously shown that dysfunction of the Nuclear factor (erythroid-derived 2)-like 2 (Nrf2)/ Kelch-like erythroid cell-derived protein 1 (Keap1) signaling pathway leads to extreme ROS imbalance during cutaneous wound healing in diabetes. Since ROS levels are an important indicator of progression of wound healing, specific and accurate quantification techniques are valuable. Several in vitro assays to measure ROS in cells and tissues have been described; however, they only provide a single cumulative measurement per sample. More recently, the development of protein-based indicators and imaging modalities have allowed for unique spatiotemporal analyses. L-012 (C13H8ClN4NaO2) is a luminol derivative that can be used for both in vivo and in vitro chemiluminescent detection of ROS generated by NAPDH oxidase. L-012 emits a stronger signal than other fluorescent probes and has been shown to be both sensitive and reliable for detecting ROS. The time lapse applicability of L-012-facilitated imaging provides valuable information about inflammatory processes while reducing the need for sacrifice and overall reducing the number of study animals. Here, we describe a protocol utilizing L-012-facilitated in vivo imaging to quantify oxidative stress in a model of excisional wound healing using diabetic mice with locally dysfunctional Nrf2/Keap1.

In Vivo Imaging of Reactive Oxygen Species in a Murine Wound Model

We describe a non-invasive in vivo imaging protocol that is streamlined and cost-effective, utilizing L-012, a chemiluminescent luminol-analog, to visualize and quantify reactive oxygen species (ROS) generated in a mouse excisional wound model.

The generation of reactive oxygen species (ROS) is a hallmark of inflammatory processes, but in excess, oxidative stress is widely implicated in various ...

A High-throughput Shigella-specific Bactericidal Assay

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing activity by assessing the ability of antibodies in serum to bind to bacteria and activate complement. This complement activation results in the lysis and killing of the target bacteria. These assays are valuable because they go beyond quantifying antibody production to elucidate the biological functions that these antibodies have, allowing researchers to study the role that antibodies may play in preventing infection. SBAs have been used to study immune responses for many human pathogens, but there is no widely accepted methodology for Shigella at present. Historically, SBAs have been very labor-intensive, requiring many time-consuming steps to accurately quantify surviving bacteria. This protocol describes a simple, robust, and high-throughput assay that measures functional antibodies specific for Shigella in serum in vitro. The method described here offers many advantages over traditional SBAs, including the use of frozen bacterial stocks, 96 well assay plates, a micro-culture system, and automated colony-counting. All of these modifications make this assay less labor-intensive and more high-throughput. This protocol is simpler and faster to perform than traditional SBAs while still using simple technologies and readily available reagents. The protocol has been successfully applied in multiple independent laboratories and the assay is robust and reproducible. The assay can be used to assess immune responses in pre-clinical as well as clinical studies. Quantifying shigellacidal antibody titers both before and after antigen exposure (either by immunization or infection) allows for a broader understanding of how functional antibody responses are generated and their contribution to protective immunity. The development of this standardized, well-characterized assay may greatly facilitate Shigella vaccine design.

A High-throughput Shigella-specific Bactericidal Assay

Here we present a protocol to measure Shigellacidal activity of antibodies in serum. Serum is mixed with bacteria and exogenous complement, incubated, and the reaction mixture is plated on agar plates. Viable bacteria form colonies which are counted, using an automated colony enumerator, and used to determine the bactericidal titer.

Serum bactericidal assays (SBAs) measure the functional activity of antibodies and have been used for many decades. SBAs directly measure antibody killing ...

Assessment of Acute Wound Healing using the Dorsal Subcutaneous Polyvinyl Alcohol Sponge Implantation and Excisional Tail Skin Wound Models.

Wound healing is a complex process that requires the orderly progression of inflammation, granulation tissue formation, fibrosis, and resolution. Murine models provide valuable mechanistic insight into these processes; however, no single model fully addresses all aspects of the wound healing response. Instead, it is ideal to use multiple models to address the different aspects of wound healing. Here, two different methods that address diverse aspects of the wound healing response are described. In the first model, polyvinyl alcohol sponges are subcutaneously implanted along the mouse dorsum. Following sponge retrieval, cells can be isolated by mechanical disruption, and fluids can be extracted by centrifugation, thus allowing for a detailed characterization of cellular and cytokine responses in the acute wound environment. A limitation of this model is the inability to assess the rate of wound closure. For this, a tail skin excision model is utilized. In this model, a 10 mm x 3 mm rectangular piece of tail skin is excised along the dorsal surface, near the base of the tail. This model can be easily photographed for planimetric analysis to determine healing rates and can be excised for histological analysis. Both described methods can be utilized in genetically altered mouse strains, or in conjunction with models of comorbid conditions, such as diabetes, aging, or secondary infection, in order to elucidate wound healing mechanisms.

Here, two murine wound healing models are described, one designed to assess cellular and cytokine wound healing responses and the other to quantify the rate of wound closure. These methods can be used with complex disease models such as diabetes to determine mechanisms of various aspects of poor wound healing.

Wound healing is a complex process that requires the orderly progression of inflammation, granulation tissue formation, fibrosis, and resolution. Murine ...

Establishing a Porcine Ex Vivo Cornea Model for Studying Drug Treatments against Bacterial Keratitis

When developing novel antimicrobials, the success of animal trials is dependent on accurate extrapolation of antimicrobial efficacy from in vitro tests to animal infections in vivo. The existing in vitro tests typically overestimate antimicrobial efficacy as the presence of host tissue as a diffusion barrier is not accounted for. To overcome this bottleneck, we have developed an ex vivo porcine corneal model of bacterial keratitis using Pseudomonas aeruginosa as a prototypic organism. This article describes the preparation of the porcine cornea and protocol for establishment of the infection. Bespoke glass molds enable straightforward setup of the cornea for infection studies. The model mimics in vivo infection as bacterial proliferation is dependent on the ability of the bacterium to damage corneal tissue. Establishment of infection is verified as an increase in the number of colony forming units assessed via viable plate counts. The results demonstrate that infection can be established in a highly reproducible fashion in the ex vivo corneas using the method described here. The model can be extended in the future to mimic keratitis caused by microorganisms other than P. aeruginosa. The ultimate aim of the model is to investigate the effect of antimicrobial chemotherapy on the progress of bacterial infection in a scenario more representative of in vivo infections. In so doing, the model described here will reduce the use of animals for testing, improve success rates in clinical trials and ultimately enable rapid translation of novel antimicrobials to the clinic.

This article describes a step-by-step protocol to set up an ex vivo porcine model of bacterial keratitis. Pseudomonas aeruginosa is used as a prototypic organism. This innovative model mimics in vivo infection as bacterial proliferation is dependent on the ability of the bacterium to damage corneal tissue.

When developing novel antimicrobials, the success of animal trials is dependent on accurate extrapolation of antimicrobial efficacy from in vitro tests to ...