The image shows the results
of a Kirby-Bauer disk diffusion antibiotic-susceptibility test. Antibiotic-impregnated
disks (containing various antibiotics) are
placed onto the agar surface, which contains
a "lawn" of growing bacteria
isolated from a bull shark caught in Louisiana waters. As the bacteria
on the lawn grow, the antibiotic diffusing from the disks inhibits its growth
varying degrees. As indicated by the varying zones of growth inhibition surrounding
each disk, the Gram-negative bacteria isolated from the shark are resistant to
some of the antibiotics in the disks at the concentrations tested. The
diameter of the inhibition zone identifies the bacteria as "susceptible," "intermediate,"
or "resistant" to specific concentrations of an antibiotic.
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