After 24 hours of growth, this image depicts four different agar media culture plates that had been inoculated with Shigella sp., Escherichia sp., and Proteus sp. bacteria, (clockwise: MacConkey, Shigella-Salmonella, Bismuth Sulfite, and Brilliant Green agars).

Differences in the constituents, which compose the various agar media, are used as determinants as to which bacteria are fostered on each culture plate. Thriving culture colonies on one type of medium may not thrive on another type of medium based on the agars’ ingredients, which a given bacterium will require to maintain life.

Image source: Centers for Disease Control and Prevention Publich Health Image Library.

This image is a work of the Centers for Disease Control and Prevention, part of the United States Department of Health and Human Services, taken or made as part of an employee's official duties. As a work of the U.S. federal government, the image is in the public domain.