We thank Ingrid Barta for histology services.

All animal protocols were approved by the Animal Care Committee of the University of British Columbia.
1. Preparation of Salmonella Typhimurium &#916;AroA cultures for oral gavage of mice
<ol>
	<li>From a frozen glycerol stock of S. Typhimurium &#916;AroA, prepare a streak plate using LB agar containing 100 &#956;g/mL streptomycin with a sterile inoculating loop. Incubate overnight at 37 &#730;C. Streak plates can be stored up to one week at 4 &#730;C.</li>
	<li>One day pri...

<ol>
	<li>Danese, S., Fiocchi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ulcerative+colitis.">Ulcerative colitis.</a> New England Journal of Medicine. 365 (18), 1713-1725 (2011).</li><li>Baumgart, D. C., Sandborn, 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=Crohn's+disease.">Crohn's disease.</a> The Lancet. 380 (9853), 1590-1605 (2012).</li><li>Knights, D., Lassen, K. G., Xavier, R. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Advances+in+inflammatory+bowel+disease+pathogenesis:+linking+host+genetics+and+the+microbiome.">Advances in inflammatory bowel disease pathogenesis: linking host genetics and the microbiome.</a> Gut. 62 (10), 1505-1510 (2013).</li><li>Xavier, R. J., Podolsky, D. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Unravelling+the+pathogenesis+of+inflammatory+bowel+disease.">Unravelling the pathogenesis of inflammatory bowel disease.</a> Nature. 448 (7152), 427-434 (2007).</li><li>Cho, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+genetics+and+immunopathogenesis+of+inflammatory+bowel+disease.">The genetics and immunopathogenesis of inflammatory bowel disease.</a> Nature Reviews Immunology. 8 (6), 458-466 (2008).</li><li>Ogura, Y., 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+frameshift+mutation+in+NOD2+associated+with+susceptibility+to+Crohn's+disease.">A frameshift mutation in NOD2 associated with susceptibility to Crohn's disease.</a> Nature. 411 (6837), 603-606 (2001).</li><li>Jostins, 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=Host-microbe+interactions+have+shaped+the+genetic+architecture+of+inflammatory+bowel+disease.">Host-microbe interactions have shaped the genetic architecture of inflammatory bowel disease.</a> Nature. 491 (7422), 119-124 (2012).</li><li>Rivas, M. 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=Deep+resequencing+of+GWAS+loci+identifies+independent+rare+variants+associated+with+inflammatory+bowel+disease.">Deep resequencing of GWAS loci identifies independent rare variants associated with inflammatory bowel disease.</a> Nature Genetics. 43 (11), 1066-1073 (2011).</li><li>Rioux, J. D., 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=Genome-wide+association+study+identifies+new+susceptibility+loci+for+Crohn+disease+and+implicates+autophagy+in+disease+pathogenesis.">Genome-wide association study identifies new susceptibility loci for Crohn disease and implicates autophagy in disease pathogenesis.</a> Nature Genetics. 39 (5), 596-604 (2007).</li><li>Uhlig, H. H., Powrie, F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+models+of+intestinal+inflammation+as+tools+to+understand+the+pathogenesis+of+inflammatory+bowel+disease.">Mouse models of intestinal inflammation as tools to understand the pathogenesis of inflammatory bowel disease.</a> European Journal of Immunology. 39 (8), 2021-2026 (2009).</li><li>Nell, S., Suerbaum, S., Josenhans, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+impact+of+the+microbiota+on+the+pathogenesis+of+IBD:+lessons+from+mouse+infection+models.">The impact of the microbiota on the pathogenesis of IBD: lessons from mouse infection models.</a> Nature Reviews Microbiology. 8 (8), 564-577 (2010).</li><li>Grassl, G. A., Finlay, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Pathogenesis+of+enteric+Salmonella+infections.">Pathogenesis of enteric Salmonella infections.</a> Current Opinion in Gastroenterology. 24 (1), 22-26 (2008).</li><li>Barthel, 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=Pretreatment+of+mice+with+streptomycin+provides+a+Salmonella+enterica+serovar+Typhimurium+colitis+model+that+allows+analysis+of+both+pathogen+and+host.">Pretreatment of mice with streptomycin provides a Salmonella enterica serovar Typhimurium colitis model that allows analysis of both pathogen and host.</a> Infection and Immunity. 71 (5), 2839-2858 (2003).</li><li>Grassl, G. A., Valdez, Y., Bergstrom, K., Vallance, B. A., Finlay, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chronic+Enteric+Salmonella+Infection+in+Mice+Leads+to+Severe+and+Persistent+Intestinal+Fibrosis.">Chronic Enteric Salmonella Infection in Mice Leads to Severe and Persistent Intestinal Fibrosis.</a> Gastroenterology. 134 (3), 768-780 (2008).</li><li>Hoiseth, S. K., Stocker, B. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Aromatic-dependent+Salmonella+typhimurium+are+non-virulent+and+effective+as+live+vaccines.">Aromatic-dependent Salmonella typhimurium are non-virulent and effective as live vaccines.</a> Nature. 291 (5812), 238-239 (1981).</li><li>Valdez, Y., Ferreira, R. B., Finlay, B. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Molecular+mechanisms+of+Salmonella+virulence+and+host+resistance.">Molecular mechanisms of Salmonella virulence and host resistance.</a> Current Topics in Microbiology and Immunology. 337, 93-127 (2009).</li><li>Valdez, Y., 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=Nramp1+drives+an+accelerated+inflammatory+response+during+Salmonella-induced+colitis+in+mice.">Nramp1 drives an accelerated inflammatory response during Salmonella-induced colitis in mice.</a> Cellular Microbiology. 11 (2), 351-362 (2009).</li><li>Lo, B. 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=The+orphan+nuclear+receptor+RORalpha+and+group+3+innate+lymphoid+cells+drive+fibrosis+in+a+mouse+model+of+Crohn's+disease.">The orphan nuclear receptor RORalpha and group 3 innate lymphoid cells drive fibrosis in a mouse model of Crohn's disease.</a> Science Immunology. 1 (3), eaaf8864 (2016).</li><li>Burke, J. P., 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=Fibrogenesis+in+Crohn's+disease.">Fibrogenesis in Crohn's disease.</a> American Journal of Gastroenterology. 102 (2), 439-448 (2007).</li><li>Hogan, B. 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=Repair+and+regeneration+of+the+respiratory+system:+complexity,+plasticity,+and+mechanisms+of+lung+stem+cell+function.">Repair and regeneration of the respiratory system: complexity, plasticity, and mechanisms of lung stem cell function.</a> Cell Stem Cell. 15 (2), 123-138 (2014).</li><li>Fiocchi, C., Lund, P. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Themes+in+fibrosis+and+gastrointestinal+inflammation.">Themes in fibrosis and gastrointestinal inflammation.</a> American Journal of Physiology-Gastrointestinal and Liver Physiology. 300 (5), G677-G683 (2011).</li><li>Rieder, F., Fiocchi, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intestinal+fibrosis+in+IBD&#8212;a+dynamic,+multifactorial+process.">Intestinal fibrosis in IBD&#8212;a dynamic, multifactorial process.</a> Nature Reviews Gastroenterology &amp; Hepatology. 6 (4), 228-235 (2009).</li><li>Bouguen, G., Peyrin-Biroulet, L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Surgery+for+adult+Crohn's+disease:+what+is+the+actual+risk?.">Surgery for adult Crohn's disease: what is the actual risk?.</a> Gut. 60 (9), 1178-1181 (2011).</li><li>Wynn, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Cellular+and+molecular+mechanisms+of+fibrosis.">Cellular and molecular mechanisms of fibrosis.</a> The Journal of Pathology. 214 (2), 199-210 (2008).</li><li>Junqueira, L. C., Bignolas, G., Brentani, R. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Picrosirius+staining+plus+polarization+microscopy,+a+specific+method+for+collagen+detection+in+tissue+sections.">Picrosirius staining plus polarization microscopy, a specific method for collagen detection in tissue sections.</a> Histochem J. 11 (4), 447-455 (1979).</li><li>Lo, B. 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=IL-22+Preserves+Gut+Epithelial+Integrity+and+Promotes+Disease+Remission+during+Chronic+Salmonella+Infection.">IL-22 Preserves Gut Epithelial Integrity and Promotes Disease Remission during Chronic Salmonella Infection.</a> Journal of Immunology. 202 (3), 956-965 (2019).</li><li>Fichtner-Feigl, 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=Induction+of+IL-13+triggers+TGF-beta1-dependent+tissue+fibrosis+in+chronic+2,4,6-trinitrobenzene+sulfonic+acid+colitis.">Induction of IL-13 triggers TGF-beta1-dependent tissue fibrosis in chronic 2,4,6-trinitrobenzene sulfonic acid colitis.</a> Journal of Immunology. 178 (9), 5859-5870 (2007).</li><li>Fichtner-Feigl, 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=IL-13+signaling+via+IL-13R+alpha2+induces+major+downstream+fibrogenic+factors+mediating+fibrosis+in+chronic+TNBS+colitis.">IL-13 signaling via IL-13R alpha2 induces major downstream fibrogenic factors mediating fibrosis in chronic TNBS colitis.</a> Gastroenterology. 135 (6), e2001-e2007 (2013).</li><li>Johnson, L. 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=Intestinal+fibrosis+is+reduced+by+early+elimination+of+inflammation+in+a+mouse+model+of+IBD:+impact+of+a+&amp;#34;Top-Down&amp;#34;+approach+to+intestinal+fibrosis+in+mice.">Intestinal fibrosis is reduced by early elimination of inflammation in a mouse model of IBD: impact of a &amp;#34;Top-Down&amp;#34; approach to intestinal fibrosis in mice.</a> Inflammatory Bowel Diseases. 18 (3), 460-471 (2012).</li><li>Darfeuille-Michaud, 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=High+prevalence+of+adherent-invasive+Escherichia+coli+associated+with+ileal+mucosa+in+Crohn's+disease.">High prevalence of adherent-invasive Escherichia coli associated with ileal mucosa in Crohn's disease.</a> Gastroenterology. 127 (2), 412-421 (2004).</li><li>Small, C. L., Reid-Yu, S. A., McPhee, J. B., Coombes, B. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Persistent+infection+with+Crohn's+disease-associated+adherent-invasive+Escherichia+coli+leads+to+chronic+inflammation+and+intestinal+fibrosis.">Persistent infection with Crohn's disease-associated adherent-invasive Escherichia coli leads to chronic inflammation and intestinal fibrosis.</a> Nature Communications. 4, 1957 (2013).</li><li>Imai, 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=Flagellin-mediated+activation+of+IL-33-ST2+signaling+by+a+pathobiont+promotes+intestinal+fibrosis.">Flagellin-mediated activation of IL-33-ST2 signaling by a pathobiont promotes intestinal fibrosis.</a> Mucosal Immunology. , (2019).</li></ol>

Our understanding of the pathogenesis of IBD has been greatly enhanced by mouse models of intestinal inflammation. Although such individual models do not recapitulate all features of the complex and multifactorial human disease, they have been useful in identifying key features of disease progression. Fibrotic strictures associated with IBD remains a major unmet clinical need as current treatments are ineffective in reversing disease development. Moreover, intestinal fibrosis is difficult to study in a laboratory setting...

Ulcerative colitis (UC) and Crohn&#8217;s disease (CD) are the two major forms of IBD and are characterized as chronic and relapsing inflammatory disorders of the gastrointestinal tract 1,2. These disorders have a major impact on the quality of life of patients. Symptoms of IBD include abdominal pain, diarrhea, nausea, weight loss, fever, and fatigue3. Recent studies have identified genetic and environmental factors that contribute to disease pathogenesis; it is thought that such risk factors contribute to the disruption of the epithelial barrier resulting in the translocation or oversampling of luminal antigens4. As a consequence, this initiates an aberrant inflammatory response to the commensal flora mediated by intestinal immune cells4. Features of IBD-associated complications may extend to sites beyond the GI tract affecting various organs including joints, skin, and liver1,2. Hallmarks of UC include severe and diffuse inflammation typically localized in the colon1. Disease pathology affects the mucosa and submucosa of the bowel resulting in superficial mucosal ulcerations1. In contrast, CD can affect any part of the GI tract although evidence of disease is commonly found in the colon and distal ileum2. Moreover, the inflammation in CD is transmural, affecting all layers of the bowel wall2.
Several IBD susceptibility genes that have been identified would indicate that dysregulation of the epithelial barrier or immunity are critical contributors to disease progression5. Mutations in nucleotide oligomerization domain 2 (NOD2) expressed by monocytes was found to be associated with increased susceptibility to CD; this highlights a link between altered innate immune detection of bacterial components and the disease6. More recent genome-wide association studies (GWAS) have revealed additional pathways potentially involved in the pathogenesis of IBD including genetic variations in: STAT1, NKX2-3, IL2RA, IL23R dependent pathways linked to adaptive immunity, MUC1, MUC19, and PTGER4 in intestinal barrier maintenance, and ATG16L-mediated autophagy7,8,9. While these population-based genetics studies have enhanced our understanding of IBD, susceptibility alleles alone are likely insufficient in initiating and sustaining chronic disease3. Other non-genetic factors including alterations in gut microbiome composition and a reduction in diversity have been associated with intestinal inflammation. However, it is unclear whether gut dysbiosis precedes or is the consequence of dysregulated immune responses3. Although the etiology of IBD remains unclear, our understanding of the pathogenesis of the disease has been enhanced by experimental mouse models of intestinal inflammation10,11. These models individually do not fully represent the complexity of the human disease, but they are valuable for elucidating pathophysiological pathways that could be relevant to IBD and for the validation of tentative therapeutic strategies10,11. Such mouse models typically rely on the initiation of inflammation by chemical induction or infection, immune cell transfer, or genetic manipulation. Moreover, these strategies often involve perturbations in epithelial integrity or modulation of innate or adaptive immunity.
Salmonella enterica serovars are intestinal pathogens that can infect humans and mice. After ingestion, Salmonella can colonize the gut by direct invasion of epithelia, M cells, or antigen presenting cells12. Mice infected orally with S. Typhimurium results in the colonization primarily of systemic sites such as the spleen and mesenteric lymph nodes with relatively low abundance in the GI tract12. However, pretreatment of mice with streptomycin enhances the efficiency of Salmonella colonization of the gut by diminishing the host protective effects of the normal microbiota13. Pathological features of this model include the disruption or ulceration of the epithelial barrier, granulocyte recruitment, and severe edema13. Alternatively, infection with the vaccine grade S. Typhimurium &#916;AroA mutant leads to chronic colonization of the cecum and colon that persists up to day 40 after infection14. The S. Typhimurium &#916;AroA strain has a defect in the biosynthesis of aromatic amino acids; this renders the mutant strain avirulent and can be utilized as a highly effective vaccine15. Oral infection in mice leads to a Th1- and Th17-cytokine associated inflammatory response, extensive tissue remodeling, and collagen deposition. Tissue pathology is associated with elevated levels of pro-fibrotic factor such as TGF-&#946;1, CTGF, and IGF14. The transmural fibrotic scarring reported in this model is reminiscent of stricture formations often observed in IBD. The induction of fibrosis by Salmonella requires virulence encoded by Salmonella pathogenicity islands (SPI)-1 and 2 12. Importantly, this S. Tymphimurium &#916;AroA infection model is a useful system for the study of fibrotic responses in mutant mice maintained on a C57/Bl6 background. The C57/Bl6 strain is extremely sensitive to S. Typhiumurim SL1344 infection due to a loss-of-function mutation in the gene encoding the natural resistance-associated macrophage protein (NRAMP)-116,17. We have found that IL-17A and ROR&#945;-dependent innate lymphoid cells are important contributors to pathogenesis in this model18.
A major complication of CD is the dysregulated and excessive deposition of extracellular matrix (ECM) including collagen2,19. Although the GI tract has a relatively high capacity for regeneration, fibrotic scarring can arise due to unresolved wound healing responses that are associated with chronic and severe inflammation20,21. In CD, this results in deleterious effects on tissue architecture leading to significant organ impairment21,22. The transmural nature of the inflammation observed in CD ultimately precedes the thickening of the bowel wall associated with symptomatic stenosis or stricture formation21. About a third of CD patients require intestinal resection for this complication22. There are no effective anti-fibrotic therapies in IBD given that the use of immunosuppressants such as azathioprine or anti-TNF&#945; biologics have no impact or only modestly reduced the requirement of surgical interventions19,23. While fibrosis is thought be the consequence of chronic inflammation, cells of mesenchymal origin such as fibroblasts and pericytes are thought to be the primary cellular sources of ECM in fibrotic scarring21,24. Chronic S. Typhimurium &#916;AroA infection is a robust mouse model of intestinal fibrosis that can offer insights into the pathogenesis of CD-like features.

<table>
	<tbody>
		<tr>
			<td>2 ml round bottom safe lock tubes</td>
			<td>Eppendorf</td>
			<td>22363344</td>
			<td></td>
		</tr>
		<tr>
			<td>Stainless steel beads</td>
			<td>Qiagen</td>
			<td>69989</td>
			<td></td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>Gibco</td>
			<td>10010031</td>
			<td></td>
		</tr>
		<tr>
			<td>Large-Orifice Pipet Tips</td>
			<td>Fisher</td>
			<td>2707134</td>
			<td></td>
		</tr>
		<tr>
			<td>2 mL megablock plates</td>
			<td>Sarstedt</td>
			<td>82.1972.002</td>
			<td></td>
		</tr>
		<tr>
			<td>Gavage needles</td>
			<td>FST</td>
			<td>18061-22</td>
			<td></td>
		</tr>
		<tr>
			<td>Streptomycin sulfate</td>
			<td>Sigma</td>
			<td>S9137</td>
			<td></td>
		</tr>
		<tr>
			<td>Mixer mill</td>
			<td>Retsch</td>
			<td>MM</td>
			<td></td>
		</tr>
	</tbody>
</table>

chronic salmonella infection induced intestinal fibrosis

Tissue fibrosis characterized by the pathological accumulation of extracellular matrix such as collagen is the outcome of persistent inflammation and dysregulated repair. In inflammatory bowel disease (IBD), fibrosis leads to recurrent stricture formations for which there is no effective therapy other than surgical resection. Due to its late onset, the processes that drive fibrosis is less studied and largely unknown. Therefore, fibrotic complications represent a major challenge in IBD. In this protocol, a robust in vivo model of intestinal fibrosis is described where streptomycin pre-treatment of C57Bl/6 mice followed by oral gavage with vaccine grade Salmonella Typhimurium &#916;AroA mutant leads to persistent pathogen colonization and fibrosis of the cecum. Methodologies for preparing S. Typhimurium &#916;AroA for inoculation, quantifying pathogen loads in the cecum and spleen, and evaluating collagen deposition in intestinal tissues are explained. This experimental disease model is useful for examining host factors that either enhance or exacerbate CD-like intestinal fibrosis.

Streptomycin treatment followed by oral infection with S. Typhimurium &#916;AroA leads to robust intestinal inflammation and fibrosis especially in the cecum (Figure 1). Typical pathogen burdens of 108 to 109 CFU per 1 g of cecum and 104 CFU per 1 g of spleen can be recovered from infected animals (Figure 2). Assessment of fibrosis in picrosirius red stained cecal sections indicate peak fibrosis 21 days after infection w...

Watch this Scientific Journal Video about Chronic Salmonella Infection Induced Intestinal Fibrosis at JoVE.com

Chronic Salmonella Infection Induced Intestinal Fibrosis

This protocol describes a mouse model of Salmonella driven intestinal fibrosis that resembles key pathological hallmarks of Crohn&#8217;s disease including transmural inflammation and fibrosis. This method can be used to evaluate host factors that alter fibrotic outcomes using mutant mice maintained on a C57Bl/6 genetic background.

Tissue fibrosis characterized by the pathological accumulation of extracellular matrix such as collagen is the outcome of persistent inflammation and ...

Tissue fibrosis is the primary way that organs fail over time, in response to chronic inflammation or aging. And in fact, I would argue that if you don't die from an infectious agent or cancer, you'll likely die from organ fibrosis as you age. Unfortunately, there're not a lot of great mouse models to mimic human tissue fibrosis.So what we've developed is a mouse model of Crohn's disease, that's a disease in human that causes fibrosis of the gut and is largely untreatable. In fact, the only way you can treat it is through surgical removal of the fibrotic tissue and re-ligation of the gut. The advantage of our model is that it's fully penetrant in all mouse strains and it very closely mimics human Crohn's disease and the fibrosis persists for over a month, which is really a robust model.The most challenging part of this procedure is the handling of the mice and especially the oral gavage since that requires a lot of practice special certification. When performing this procedure for the first time, one should be aware that working with Salmonella requires proper safety precautions and sterile technique. Disposal of waste and bacteria should all be planned prior to the experiment.The visual demonstration of this procedure is very important because it involves the handling of Salmonella that requires special safety precautions as well as proper sterile technique. To begin this procedure, set out a plate with LB agar containing Streptomycin at a concentration of 100 micrograms per milliliter. Using a sterile inoculating loop, streak the plate with a frozen glycerol stock of S typhimurium delta arrow a.Incubate overnight at 37 degrees Celsius. Streak plates can be stored at four degrees Celsius for up to one week. One day prior to infection, dissolve 0.5 grams of Streptomycin in 2.5 milliliters of water to prepare the antibiotic.Filter sterilize the Streptomycin solution. Then, use a bulb-tipped 22 gauge gavage needle with a one milliliter syringe to orally gavage the mice with 100 microliters of the streptomycin solution. Next, add three milliliters of LB broth containing Streptomycin at a concentration of 50 micrograms per milliliter to a culture tube.Using an inoculation loop, inoculate the LB broth with a single colony. Incubate the culture aerobically overnight at 37 degrees Celsius with shaking at 200 rpm. On the day of infection, perform two consecutive one to 10 dilutions of the overnight Salmonella cultures with sterile PBS to prepare the final infection dose.This results in a 100 microliter inoculum containing approximately three million colony forming units. After this, use a bulb-tipped 22 gauge gavage needle with a milliliter syringe to gavage each mouse with 100 microliters of the prepared Salmonella. First, set out two milliliter safe-lock round bottom microtubes, add one milliliter of sterile PBS and an autoclaved stainless steel bead to each tube.Pre-weigh the tubes prior to tissue collection. After euthanizing mice, resect their cecal and splenic tissues, making sure to collect tissue from individual animals into separate tubes. Weigh each tube to determine the tissue weights.Use a mixer mill apparatus to homogenize the tissues at 30 hertz for 15 minutes. Then, transfer 900 microliters of PBS into each well of a 96-well two milliliter mega block. Pipette 100 microliters of tissue homogenates into the first well, and mix well.Perform serial dilutions by adding 100 microliters to subsequent wells, until a 10 to the negative sixth dilution is obtained. Plate 10 microliters of each dilution in triplicates onto LB agar that contains Streptomycin. Then, count the average colony forming units and determine the colony forming units per gram of tissue as outlined in the text protocol.Open Fiji, which is an open sourced imaging software and drag and drop the tif image file onto the tool bar. On the menu bar, select Image, Type, RGB stack to split the image into red, green and blue channels. Slide the horizontal bar at the bottom of the panel to set the channel to green.Open Image, Adjust, Threshold tool. Adjust minimum and maximum limits to eliminate any background signals. Once the desired threshold is set, close the threshold tool and go to Analyze, Set Measurements, check off Area, Area fraction, Limit to threshold and Display label.Get the tissue selection with either the freehand selections or polygon selections tool and measure the percent area positive for collagen by clicking Analyze, Measure. Then, normalize the absolute area positive for collagen staining to tissue area. Streptomycin treatment followed by oral infection with S typhimurium delta arrow a leads to robust intestinal inflammation and fibrosis, especially in the cecum.Typical pathogen burdens of 100 million to one billion colony forming units can be recovered per gram of cecum from infected animals, while 10 thousand colony forming units can typically be recovered per gram of spleen. Assessment of fibrosis in picrosirius red stained cecal sections indicates peak fibrosis 21 days after infection, while much of the pathology is resolved by day 42 post infection. Thorough preparation of materials is essential as this experiment requires multiple days to set up.Preparation of LB plates and Salmonella and Streptomycin should all be done aseptically. Prior to the experiment, ensure that the experimenter is familiar with the animal protocol as well as safety hazards. Upon assessing the collagen burden, the experimenter may choose to perform other biological assays, such as RNA sequencing to assess gene expression profiles or flow cytometry to assess immune cell subsets or a tissue ELISA to assess cytokine profiles.So our model is particularly good at mimicking a human disease called Crohn's disease where you get fibrosis of the gut, which is largely untreatable and the only way you can treat it is to remove a section of the gut and stitch it back together and hope it doesn't come back. Our model's very robust and we've already shown that targeting innate lymphoid cells type three, a transcription factor called raw alpha, or interleukin 17 ameliorates the disease and prevents the fibrosis. Our model is particularly good at identifying the factors that play in the pathogenesis of Crohn's disease and gut fibrosis and we're already on the road to identifying a number of targets that could be treated therapeutically to alleviate inflammatory bowel disease.Our model has already entered the same ILC3 or alpha NIL17 access may be at play in other fibrotic disease and these include things like psoriasis, multiple sclerosis, idiopathic pulmonary fibrosis. So it's possible that targeting these same factors might alleviate fibrosis in those diseases as well. Although the mutant Salmonella stream isn't virulent, it is important to follow the standard biohazard safety protocols given by the facility.Also, since formaldehyde vapors are known to be carcinogenic, it's important to work behind a fume hood during the fixation step.

chronic-salmonella-infection-induced-intestinal-fibrosis

Research

JoVE Journal

Immunology and Infection

6.8K Views.  University of British Columbia. Tissue fibrosis is the primary way that organs fail over time, in response to chronic inflammation or aging. And in fact, I would argue that if you don't die from an infectious agent or cancer, you'll likely die from organ fibrosis as you age. Unfortunately, there're not a lot of great mouse models to mimic human tissue fibrosis.So what we've developed is a mouse model of Crohn's disease, that's a disease in human that causes fibrosis of the gut and is largely untreatable. In fact, the...