Name: intravitreal injection and quantitation of infection parameters in a mouse model of bacterial endophthalmitis
Uploaded: 2021-02-06T13:00:00
Description: Watch this Scientific Journal Video about Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis at JoVE.com

The authors thank Dr. Feng Li and Mark Dittmar (OUHSC P30 Live Animal Imaging Core, Dean A. McGee Eye Institute, Oklahoma City, OK, USA) for their assistance. Our research has been supported by National Institutes of Health grants R01EY028810, R01EY028066, R01EY025947, and R01EY024140. Our research has also been supported by P30EY21725 (NIH CORE grant for Live Animal Imaging and Analysis, Molecular Biology, and Cellular Imaging). Our research has also been supported by the NEI Vision Science Pre-doctoral Trainee program 5T32EY023202, a Presbyterian Health Foundation Research Support grant, and an unrestricted grant to the Dean A. McGee Eye Institute from Research to Prevent Blindness.

All procedures were performed following the recommendations in the Guide for the Care and Use of Laboratory Animals and the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research. The protocols were approved by the Institutional Animal Care and Use Committee of the University of Oklahoma Health Sciences Center (protocol numbers 15-103, 18-043, and 18-087).
1. Sterile glass needles
<ol>
	<li>Turn On the needle p...

Even with the availability of potent antibiotics, anti-inflammatory drugs, and vitrectomy surgery, bacterial endophthalmitis can blind a patient. Clinical studies have been useful in studying endophthalmitis; however, experimental models of endophthalmitis provide quick and reproducible results that can be translated to progress in standard of care, resulting in better visual outcome for patients.
The vitreous volume of the mouse eye is approximately 7 &#181;L40. This s...

Bacterial endophthalmitis is a devastating infection that causes inflammation, and, if not treated properly, can result in loss of vision or blindness. Endophthalmitis results from the entry of bacteria into the interior of the eye1,2,3,4,5. Once in the eye, bacteria replicate, produce toxins and other noxious factors, and can cause irreversible damage to delicate retinal cells and tissues. Ocular damage can also be caused by inflammation, due to the activation of inflammatory pathways leading to inflammatory cell influx into the interior of the eye1,5,6. Endophthalmitis can occur following intraocular surgery (post-operative), a penetrating injury to the eye (post-traumatic), or from metastatic spread of bacteria into the eye from a different anatomical site (endogenous)7,8,9,10. Treatments for bacterial endophthalmitis includes antibiotics, anti-inflammatory drugs, or surgical intervention3,4,11. Even with these treatments, vision or the eye itself may be lost. The visual prognosis after bacterial endophthalmitis generally varies depending upon the treatment effectiveness, the visual acuity at presentation, and the virulence of the infecting organism.
Bacillus cereus (B. cereus) is one of the major bacterial pathogens that causes post-traumatic endophthalmitis7,12. A majority of B. cereus endophthalmitis cases have a rapid course, which can result in blindness within a few days. The hallmarks of B. cereus endophthalmitis include quickly evolving intraocular inflammation, eye pain, rapid loss of visual acuity, and fever. B. cereus grows rapidly in the eye compared to other bacteria which commonly cause eye infections2,4,12 and possesses many virulence factors. Therefore, the window for successful therapeutic intervention is relatively short1,&#160;2,&#160;3,&#160;4,&#160;5,&#160;6,&#160;7,&#160;11,&#160;12,&#160;13,&#160;14,&#160;15,&#160;16,&#160;17,&#160;18,&#160;19,&#160;20,&#160;21,&#160;22,&#160;23,&#160;24,&#160;25. Treatments for this infection are usually successful in treating endophthalmitis caused by other less virulent pathogens, but B. cereus endophthalmitis commonly results in greater than 70% of patients suffering from significant vision loss. About 50% of those patients undergo evisceration or enucleation of the infected eye7,16,22,23. The destructive and rapid nature of B. cereus endophthalmitis calls for immediate and proper treatment. Recent progress in discerning the underlying mechanisms of disease development have identified potential targets for intervention19,26,27. Experimental mouse models of B. cereus endophthalmitis continue to be useful in discerning the mechanisms of infection and testing potential therapeutics that may prevent vision loss.
Experimental intraocular infection of mice with B. cereus has been an instrumental model for understanding bacterial and host factors, as well as their interactions, during endophthalmitis28. This model mimics a post-traumatic or post-operative event, in which bacteria are introduced into the eye during an injury. This model is highly reproducible and has been useful for testing experimental therapies and providing data for improvements in standard of care1,6,19,29,30. Like many other infection models, this model allows for independent control of many parameters of infection and enables efficient and reproducible examination of infection outcomes. Studies in a similar model in rabbits over the past few decades have examined the effects of B. cereus virulence factors in the eye2,4,13,14,31. By injecting B. cereus mutant strains lacking individual or multiple virulence factors, the contribution of these virulence factors to disease severity can be measured by outcomes such as the concentration of bacteria at different hours of postinfection or the loss of visual function13,14,27,31,32. In addition, host factors have been examined in this model by infecting knockout mouse strains lacking specific inflammatory host factors26,29,33,34,35. The model is also useful for testing potential treatments for this disease by injecting novel compounds into the eye after infection30,36. In this manuscript, we describe a detailed protocol which includes infecting a mouse eye with B. cereus, harvesting the eye after infection, quantifying intraocular bacterial load, and preserving specimens to assay additional parameters of disease severity.

<table>
	<tbody>
		<tr>
			<td>2-20 &#181;L pipette</td>
			<td>RANIN</td>
			<td>L0696003G</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>37oC Incubator</td>
			<td>Fisher Scientific</td>
			<td>11-690-625D</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Bacto Brain Heart Infusion</td>
			<td>BD</td>
			<td>90003-032</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Cell Microinjector</td>
			<td>MicroData Instrument, Inc.</td>
			<td>PM2000</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Fine tip forceps</td>
			<td>Thermo Fisher Scientific</td>
			<td>12-000-122</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Glass beads 1.0 mm</td>
			<td>BioSpec</td>
			<td>11079110</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Incubator Shaker</td>
			<td>New Brunswick Scientific</td>
			<td>NB-I2400</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Microcapillary Pipets 5 Microliters</td>
			<td>Kimble</td>
			<td>71900-5</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Micro-Pipette Beveler</td>
			<td>Sutter Instrument Co.</td>
			<td>BV-10</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Microscope Axiostar Plus</td>
			<td>Zeiss</td>
			<td></td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Microscope OPMI Lumera</td>
			<td>Zeiss</td>
			<td></td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Mini-Beadbeater-16</td>
			<td>BioSpec</td>
			<td>Model 607</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Multichannel pipette 30-300 &#181;L</td>
			<td>Biohit</td>
			<td>15626090</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Multichannel pipette 5-100 &#181;L</td>
			<td>Biohit</td>
			<td>9143724</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>Needle/Pipette Puller</td>
			<td>Kopf</td>
			<td>730</td>
			<td>NA</td>
		</tr>
		<tr>
			<td>PBS</td>
			<td>GIBCO</td>
			<td>1897315</td>
			<td>Molecular grade</td>
		</tr>
		<tr>
			<td>Protease Inhibitor Cocktail</td>
			<td>Roche</td>
			<td>4693159001</td>
			<td>Molecular grade</td>
		</tr>
		<tr>
			<td>Reverse action forceps</td>
			<td>Katena</td>
			<td>K5-8228</td>
			<td>NA</td>
		</tr>
	</tbody>
</table>

intravitreal injection and quantitation of infection parameters in a mouse model of bacterial endophthalmitis

Intraocular bacterial infections are a danger to the vision. Researchers use animal models to investigate the host and bacterial factors and immune response pathways associated with infection to identify viable therapeutic targets and to test drugs to prevent blindness. The intravitreal injection technique is used to inject organisms, drugs, or other substances directly into the vitreous cavity in the posterior segment of the eye. Here, we demonstrated this injection technique to initiate infection in the mouse eye and the technique of quantifying intraocular bacteria. Bacillus cereus was grown in brain heart infusion liquid media for 18 hours and resuspended to a concentration 100 colony forming units (CFU)/0.5 &#181;L. A C57BL/6J mouse was anesthetized using a combination of ketamine and xylazine. Using a picoliter microinjector and glass capillary needles, 0.5 &#181;L of the Bacillus suspension was injected into the mid vitreous of the mouse eye. The contralateral control eye was either injected with sterile media (surgical control) or was not injected (absolute control). At 10 hours post infection, mice were euthanized, and eyes were harvested using sterile surgical tweezers and placed into a tube containing 400 &#181;L sterile PBS and 1 mm sterile glass beads. For ELISAs or myeloperoxidase assays, proteinase inhibitor was added to the tubes. For RNA extraction, the appropriate lysis buffer was added. Eyes were homogenized in a tissue homogenizer for 1-2 minutes. Homogenates were serially diluted 10-fold in PBS and track diluted onto agar plates. The remainder of the homogenates were stored at -80 &#176;C for additional assays. Plates were incubated for 24 hours and CFU per eye was quantified. These techniques result in reproducible infections in mouse eyes and facilitate quantitation of viable bacteria, the host immune response, and omics of host and bacterial gene expression.

Generating a reproducible inoculum and accuracy of the intravitreal injection procedure are key steps in developing models of microbial endophthalmitis. Here, we demonstrated the intravitreal injection procedure using Gram-positive Bacillus cereus. We injected 100 CFU/0.5 &#956;L of B. cereus into the mid-vitreous of five C57BL6 mice. After 10 h postinfection, we observed intraocular growth of B. cereus to approximately 1.8 x 105 CFU/eye. Figure 1 demons...

Watch this Scientific Journal Video about Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis at JoVE.com

Intravitreal Injection and Quantitation of Infection Parameters in a Mouse Model of Bacterial Endophthalmitis

We describe here a method of intravitreal injection and subsequent bacterial quantitation in mouse model of bacterial endophthalmitis. This protocol can be extended for measuring host immune responses and bacterial and host gene expression.

Intraocular bacterial infections are a danger to the vision. Researchers use animal models to investigate the host and bacterial factors and immune ...

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