Assessing the Antimicrobial Potential of Bacteriocin-Producing Murine Fecal Bacterial Isolates

Take mouse fecal suspension comprising lactic acid bacteria, or LAB, that produce bacteriocin, an antimicrobial peptide, and inoculate into a pre-warmed LAB selective soft agar medium.

Pour the medium into an agar plate, forming the first layer.

Overlay a second agar layer and incubate.

The first layer selectively promotes LAB growth, allowing the secreted bacteriocin molecules to diffuse outwards from the colonies into the surrounding medium. 

The second layer contains a cell-free medium that allows the diffusion of bacteriocin and prevents the growth of LAB colonies on the surface.

Now, pour a third agar layer containing a bacteriocin-sensitive strain.

The bacteria growing in the third layer encounter the bacteriocin diffusing from the lower layers. 

The bacteriocin disrupts the cell membrane of sensitive bacteria, disturbing cellular homeostasis and resulting in cell death, visible as a clear zone on the third layer.

Measure the zone diameter to assess bacteriocin potency.