Encyclopedia of Experiments: Biology
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Conjunctiva of the eye harbors commensal bacteria. This indigenous microflora protects the eye from infection by activating the immune cells to attack any harmful microbes that enter the eye linings.
To isolate commensal bacteria, place an anesthetized mouse in a lateral position. Take a sterile eye swab dipped in a suitable medium. Insert the wet swab tip into the medial conjunctival region of the left eye. Depress the eyeball and move the swab back and forth along the conjunctiva to collect a diverse commensal population.
Remove the swab and stir it into a tube containing microbial enrichment media. This step releases the entrapped bacteria from the cotton mesh of the swab into the media. Discard the swab and incubate the tube to facilitate the onset of bacterial growth.
Dispense a few drops of the eye swab inoculated enriched media onto a blood agar plate in the desired pattern and incubate. The casein and soy peptones present in the media supply nitrogen required for peptide synthesis while the sodium chloride maintains osmotic equilibrium.
Commensal bacteria possess hemolysin enzymes that digest the hemoglobin present in blood media. This produces a characteristic pattern on the agar plate, causing different bacteria to proliferate into morphologically distinct colonies. Count the number of colonies to determine their relative abundance in the conjunctiva.
