Bacterial Endophthalmitis Mouse Model: A Method for Generating Bacterial Endophthalmitis via Intravitreal Injection of Bacterial Suspension into Eye of Mouse

Bacterial endophthalmitis is an inflammatory eye infection due to intraocular invasion of Bacillus cereus bacteria.

To generate bacterial endophthalmitis in a mouse model, place an anesthetized mouse laterally on the surgery board. Clamp the periocular skin to displace the eyeball and locate the limbus region — an intersection point of sclera and cornea in the eye.

Take a needle pre-filled with the Bacillus cereus culture suspension. Insert the needle at the limbus and pierce through the mid-vitreous region. Next, inject the bacterial suspension intravitreally, releasing the bacteria into the eye's vitreous cavity.

Now, remove the needle and allow the eyeball to regain its natural position. Transfer the mouse to a cage and monitor the spread of bacterial infection. Once inside, the bacteria replicate rapidly to increase in number. Subsequently, these bacteria use their flagella to migrate toward the retina.

Upon reaching the vitreoretinal space, bacteria secrete toxins and enzymes, which help them in invading the retina. Inside the retina, bacterial envelope proteins activate the retinal muller cells, producing inflammatory mediators to recruit inflammatory cells that damage the delicate retinal cells. Eventually, an influx of inflammatory cells into the eye’s interior causes endophthalmitis in the mouse eye.

For intravitreal injection, turn on the microinjector and open the gas valve on the compressed air tank attached to the microinjector. Press 'Mode' on the injector until the screen shows 'Balance.' Press 'Balance' and place the computer mouse on the operating table. Connect the stainless-steel pipette holder to the tubing attached to the 'Fill/Output' on the injector, and tightly screw the pipette holder connector around a beveled glass capillary pipette tip needle to allow insertion of the capillary needle into the other end of the pipette holder.

Turn on the ophthalmic microscope and set the light intensity to 50%. Position the microscope over the procedure side and adjust the microscope to the desired focus. After confirming a lack of response to pedal reflux, place the anesthetized mouse on its left side on the medical underpads with the nose pointed to the right.

Locate the right eye through the ophthalmic microscope objective and place the tongs of a reverse action forceps on either side of the eye to expose the injection site. Left-click the mouse connected to the microinjector to fill the prepared capillary needle with the diluted bacterial solution, and securing the head with the left hand, place the tip of the needle, bevel-side up at the limbus of the eye.

With the needle at a 45 degree angle, puncture the eye, taking care that only 0.5 millimeters of the sharp tip of the needle is inserted. Once the needle tip has been inserted, use the left hand to right click on the mouse pad to inject 0.5 microliters of the B. cereus solution. To prevent leakage, leave the needle tip inside the mouse eye for 2 to 3 seconds before removing. Then, release the forceps and the eye will go back into the socket by itself. Transfer the mouse to a recovery cage on a warming pad with monitoring until full recumbency.