This work was supported in part by the Intramural Research Program of the National Institutes of Health, National Institute of Environmental Health Sciences (Z01 ES102005).

All experiments were performed in accordance with the Animal Welfare Act and the U.S. Public Health Service Policy on Humane Care and Use of Laboratory Animals after review by the Animal Care and Use Committee of the NIEHS.
1. Preparation of K. pneumoniae Culture
Caution: Perform all steps in a biosafety level 2 (BSL2) hood or other BSL2 designated area and discard waste per institute BSL2 guidelines.
<ol>
	<li>For suspension growth of K. pneumoniae</...

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The authors declare that they have no competing financial interests.

Murine models of bacterial pneumonia, partnered with gene targeting and in vivo biological and pharmacological interventions, have provided critical insights into the pulmonary host defense response. Great advances have been made in particular in our understanding of the chemokines and adhesion molecules that govern recruitment of neutrophils to the infected airspace10,11. In vivo models of pneumonia, unlike cell-based or alternative approaches, have also provided key insights into endocrine ...

Community-acquired pneumonia remains the leading cause of death from infection in the U.S., with little overall change in mortality rates over the past 40 years despite improvements in vaccination and antibiotic strategies1,2. Despite the lack of perceptible progress at the public health level, in recent years dramatic advances have been made in our understanding of the molecular and cellular pathogenesis of pneumonia, with many of these steps forward made possible by the use of mouse models of lung infection. The genetic tractability of the mouse, the similarity of the murine and human immune systems, and the vast array of murine-targeted immunologic reagents that have become commercially available have together facilitated rapid progress of the field.
Mouse models of bacterial pneumonia described in the literature have generally relied upon one of four technical routes for pathogen inoculation: i) aerosolization; ii) intranasal delivery; iii) peroral delivery; and iv) surgical intratracheal injection (i.e., tracheotomy)3. All routes of infection have advantages and disadvantages3. In particular, relative exposure of the upper airway, potential for admixture of oronasal flora, requirements for general anesthesia, variability of the inoculum delivered to the distal lung, lobar distribution of the delivered pathogens, technical expertise requirements, and procedural morbidity vary widely across these approaches.
Commonly used peroral infection techniques include endotracheal (translaryngeal) cannulation via either a &#39;blind&#39; (non-visualized) approach, or under direct laryngeal visualization3-5. Both methods, while robust, require substantial training and also carry risk of trauma to the upper airway. In the present report, we describe a technically non-intensive, non-invasive, inexpensive, and rapid method of peroral infection, whereby bacteria (Klebsiella pneumoniae in the example provided) pipetted into the oropharynx of an anesthetized mouse are delivered to the lungs via aspiration (i.e., inhalation). We and others have used the aspiration pneumonia technique successfully6-9. This versatile and easily learned lung-delivery method can be extended to the delivery of many additional non-caustic agents to the lungs, including cytokines and other proteins, pathogen-associated molecules (e.g., lipopolysaccharide), cells (i.e., adoptive transfer), and toxins (e.g., bleomycin). In addition to discussing important technical considerations, we also describe an integrated, quantitative approach for assessing the subsequent host response to pneumonia, including downstream measurement of bacterial clearance (i.e., colony forming unit [CFU] quantitation in the lung and peripheral organs) and leukocyte accumulation in the airspace.

<table border="0" cellpadding="0" cellspacing="0" width="698">
	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Klebsiella pneumoniae, serotype 2</td>
			<td style="width:169px;">ATCC</td>
			<td style="width:119px;">43816</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Tryptic soy broth</td>
			<td style="width:169px;">Becton Dickenson</td>
			<td>211825</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Excel Safelet IV Catheters, 18G x 1 1/4&#34;</td>
			<td>Claflin Medical Equipment</td>
			<td style="width:119px;">MEDC-031122</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Hema 3 Solution 1</td>
			<td style="width:169px;">Fisher</td>
			<td style="width:119px;">23-122-937</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Hema 3 Solution 2</td>
			<td style="width:169px;">Fisher</td>
			<td style="width:119px;">23-122-952</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Hema 3 Fixative</td>
			<td style="width:169px;">Fisher</td>
			<td style="width:119px;">23-122-929</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">27&#189; gauge tuberculin syringes</td>
			<td style="width:169px;">Fisher</td>
			<td style="width:119px;">14-826-87</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">Lithium heparin plasma collectors</td>
			<td style="width:169px;">Fisher</td>
			<td style="width:119px;">2675187</td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:243px;">L-shaped disposable spreaders</td>
			<td style="width:169px;">Lab Scientific</td>
			<td style="width:119px;">DSC</td>
			<td></td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:243px;">1x PBS, pH 7.4</td>
			<td style="width:169px;">prepared in-house</td>
			<td style="width:119px;">n/a</td>
			<td>Distilled water (5 L), NaCl (40 g), KCl (1 g), Na2HPO4 (5.75 g), KH2PO4 (1 g)&#160;&#160;&#160;</td>
		</tr>
		<tr height="25">
			<td height="25" style="height:25px;width:243px;">ACK lysis buffer</td>
			<td style="width:169px;">prepared in-house</td>
			<td style="width:119px;">n/a</td>
			<td>NH4Cl (4.145 g), KHCO3 (0.5 g), EDTA (18.6 mg), bring up to 500 ml with distilled water and pH to 7.4</td>
		</tr>
	</tbody>
</table>

a non-invasive and technically non-intensive method for induction and phenotyping of experimental bacterial pneumonia in mice

Although community-acquired pneumonia remains a major public health problem, murine models of bacterial pneumonia have recently facilitated significant preclinical advances in our understanding of the underlying cellular and molecular pathogenesis. In vivo mouse models capture the integrated physiology and resilience of the host defense response in a manner not revealed by alternative, simplified ex vivo approaches. Several methods have been described in the literature for intrapulmonary inoculation of bacteria in mice, including aerosolization, intranasal delivery, peroral endotracheal cannulation under &#39;blind&#39; and visualized conditions, and transcutaneous endotracheal cannulation. All methods have relative merits and limitations. Herein, we describe in detail a non-invasive, technically non-intensive, inexpensive, and rapid method for intratracheal delivery of bacteria that involves aspiration (i.e., inhalation) by the mouse of an infectious inoculum pipetted into the oropharynx while under general anesthesia. This method can be used for pulmonary delivery of a wide variety of non-caustic biological and chemical agents, and is relatively easy to learn, even for laboratories with minimal prior experience with pulmonary procedures. In addition to describing the aspiration pneumonia method, we also provide step-by-step procedures for assaying the subsequent in vivo pulmonary innate immune response of the mouse, in particular, methods for quantifying bacterial clearance and the cellular immune response of the infected airway. This integrated and simple approach to pneumonia assessment allows for rapid and robust evaluation of the effect of genetic and environmental manipulations upon pulmonary innate immunity.

C57BL/6 mice were infected with 2000 CFU of K. pneumoniae 43816 (serotype 2) via oropharyngeal aspiration into the lungs. At this dose, mice typically begin to show clinical symptoms 12-24 hr post-infection including lethargy, ruffled fur, and weight loss of 5-10% (Figure 2A). Within 48-72 hr post-infection, many of the mice show symptoms of illness and morbidity that is typically preceded by an average of 20% weight loss and results in hunched postures with decr...

Watch this Scientific Journal Video about A Non-invasive and Technically Non-intensive Method for Induction and Phenotyping of Experimental Bacterial Pneumonia in Mice at JoVE.com

A Non-invasive and Technically Non-intensive Method for Induction and Phenotyping of Experimental Bacterial Pneumonia in Mice

Several methods have been described in the literature for modeling bacterial pneumonia in mice. Herein, we describe a non-invasive, inexpensive, rapid method for inducing pneumonia via aspiration (i.e., inhalation) of a bacterial inoculum pipetted into the oropharynx. Downstream methods for assessment of the pulmonary innate immune response are also detailed.

Although community-acquired pneumonia remains a major public health problem, murine models of bacterial pneumonia have recently facilitated significant ...

The overall goal of this experimental protocol is to provide a non-invasive and technically non-intensive procedure for inducing bacterial pneumonia in mice and the subsequent quantification of the in vivo host defense response in the lungs. This method can help answer key questions in the fields of infectious disease and immunology, about the genes and molecular pathways that control the host response to infection. The main advantage of this lung infection method is its technical simplicity.Which allows even laboratories with little expertise in pulmonary procedures to study the pulmonary innate immune response. In a biosafety level two facility, thaw a glycerol stock of K.pneumoniae and transfer one milliliter of the bacteria into a 500 milliliter culture flask containing 50 milliliters of Tryptic Soy Broth. Incubate the suspension culture overnight at 37 degrees Celsius and 200 to 225 RPM.The next morning, dilute one to five milliliters of the bacterial culture in a new flask containing 50 milliliters of Tryptic Soy Broth, and incubate the culture, in the shaker, at 37 degrees Celsius for an additional 2.5 hours to achieve log phase. At the end of the second incubation, transfer one milliliter of bacteria from the second culture to a 1.5 milliliter tube for centrifugation. Remove the supernatant without disturbing the palette and gently resuspend the bacteria in one milliliter of sterile saline for three separate washes.After the third wash, resuspend the bacteria in another milliliter of sterile saline, and set up log-wise serial dilutions of the inoculum. Measure one milliliter of the one to 10 and one to 100 dilutions in disposable cuvettes, in duplicate, to determine the OD600 of the washed K.pneumoniae. An OD600 of 1.0 is roughly equivalent to four to seven times 10 to the eighth CFUs per milliliter.After calculating the concentration of the bacteria in each dilution, resuspend the desired inoculum CFU dose in 50 to 60 microliters of sterile saline per eight to 12 week old recipient animal. To deliver the bacteria to the animals, draw up the dosing inoculum into a P200 pipette tip, and place the anesthetized mouse in a semi-recumbent supine position, suspended by the maxillary incisors, from a rubber band stretched between the pegs of a slanted Plexiglas board. Using a pair of blunt, non-ridged forceps, gently pull the tongue to the side and deposit the dose into the animal's oral cavity taking care to avoid inducing trauma to the tongue or the oral pharynx.Keeping the tongue retracted, gently occlude the nose with a gloved finger, until the house inhales two to three times. When no liquid is visible in the oral cavity, transfer the mouse from the inoculation board to its cage, in the supine position, to prevent blockage of the nares while the mouse is recovering. Make a longitudinal cut just below the sternum.Then, lifting the sternum with forceps, nick the diaphragm, allowing the lung to fall back into the chest cavity. Continue the incision up through the chest cavity on either side of the vasculature and up through the neck. When the trachea is visible, carefully cut through the middle of the neck and push the tissue to the sides to avoid damaging the surrounding vasculiture.Now nick the trachea about one quarter of the way down from the head, and caudally insert a cannula attached to a one milliliter syringe pre-loaded with one milliliter of PBS into the trachea. Push the volume into the lungs, slowly, allowing all of the lobes to inflate. Then pull the volume back out with the syringe and pool the collected washes in a 15 milliliter tube, on ice.At the appropriate experimental end point, collect the blood from the left ventricle and transfer it into a heparinized tube to avoid clotting. Then harvest all of the lung lobes in a 15 milliliter tube containing five milliliters of PBS, and the spleen in a 15 milliliter tube containing two milliliters of PBS. Next, use individual, disposable homogenizers per sample, to macerate the tissues on ice, followed by serial dilution of the tissue slurries.Plate the dilutions, in duplicate, on separate sides of a single TSA plate, and allow the samples to, briefly, dry. Then invert the plates and culture the samples in a static 37 degrees Celsius incubator overnight, averaging the bacterial colonies from both sides of the plate and from each dilution the next morning. At 2000 CFU of K.pneumoniae, mice, typically, begin to demonstrate clinical symptoms 12 to 24 hours post infection.Within 48 to 72 hours, many of the animals exhibit symptoms of illness and morbidity that are typically preceded by an average of 20 percent weight loss. An LD50 dose, however, allows the detection of both the relatively increased and decreased survival within the experimental group, and may be preferred for longer term studies. Lower respiratory tract infection with K.pneumoniae is characterized by a robust influx of leukocytes into the airway within six hours of infection, that peaks by 24 hours and is mostly represented by neutrophils.Cytokines are detectable in the bronchoalveolar lavage fluid at both 24 and 48 hours post infection with K.pneumoniae, and provide insight into the lung microenvironment and its immune self-recruitment in response to bacterial invasion. The bacterial load in the lung, blood, and spleen, also dramatically increases between 24 and 48 hours of infection. Once mastered, the oropharyngeal aspiration method of lung infection can be done in just one to two minutes per mouse if it is performed properly.While attempting this procedure, it is important to remember not to use an excessive aspiration volume. A 50 to 60 microliter volume typically works well for an eight to 12 week old mouse. Following this procedure, a variety of methods can be performed on the lung and peripheral tissues to allow the quantification of the immune response in pathogen clearance.After watching this video you should have a good understanding of how to induce experimental bacterial pneumonia via oropharyngeal pathogen delivery and to determine the pathogen burden in mice. Don't forget that working with microbes can be hazardous and that basic BSL-2 precautions and practices should always be taken while preforming this procedure.

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Immunology and Infection

8.8K vistas.  National Institutes of Health. The overall goal of this experimental protocol is to provide a non-invasive and technically non-intensive procedure for inducing bacterial pneumonia in mice and the subsequent quantification of the in vivo host defense response in the lungs. This method can help answer key questions in the fields of infectious disease and immunology, about the genes and molecular pathways that control the host response to infection. The main advantage of this lung infection method is its technical simplicity....