University of Pennsylvania Medical Center Guidelines
for Antibiotic Use
Pictured above is a graph which shows the relationship between
the MIC and the size of the zone of inhibition
in the Bauer-Kirby test for the drug-A using
the bacteria-Q. "R" represents the cutoff for the interpretation of
"resistant", and "S" represents the cutoff for the interpretation of
The portion of the curve which is green represents the region where
it would be reported that bacteria-Q is susceptible to drug-A.
Refection of the curve onto the X-axis (dotted green lines) show that
a zone diameter greater than 23 mm
(green arrow) is required for "susceptible" to be reported out
for this bug/drug pair. This correlates approximately with an MIC of
< 8 micrograms.