Assessing Bacterial Colonization in a Mouse Brain following Listeria monocytogenes Infection

Take a perfused mouse brain in buffer.

The brain is infected with streptomycin-resistant Listeria monocytogenes, a pathogenic bacterium.

The perfusion step removes blood from the brain, ensuring that bacterial burden measurements reflect the load of Listeria monocytogenes in the tissue.

Next, homogenize the brain using a sterilized homogenizer to break down the tissue and release bacteria.

Now, prepare serial dilutions of the brain homogenate using buffer.

Plate these dilutions on brain heart infusion agar plates containing streptomycin, an antibiotic.

Incubate the plates. The brain heart infusion agar provides nutrients for Listeria monocytogenes growth, while streptomycin selects for resistant bacteria, allowing only streptomycin-resistant Listeria colonies to form.

Count the number of colonies on the plate to determine the colony-forming units, a measure of viable infective bacterial load in the brain.

Using forceps, open the skull to expose the brain and place a spatula between the underside of the brain and the base of the skull to carefully transfer the brain into a 15 milliliter tube containing 5 milliliters of 4 degrees Celsius PBS.

In a biosafety cabinet, insert the tip an