Download RESULTS: Kirby Bauer Antibiotic Sensitivity Test

RESULTS: Kirby Bauer Antibiotic Sensitivity Test/ Snyder Test
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The S. aureus (Gram +) plate:
The S. aureus bacteria have
zones of inhibition for all
antibiotics tested (in fact, they
overlap and can’t be measured).
The only place that growth is
seen is in the middle of the plate.
The P. aeruginosa (Gram-) plate:
Many of the antiobiotics did not
develop zones of inhibition and
are resistant.
The E. coli (Gram -) plate: In the
Kirby-Bauer table, E. coli is
found under
“Enterobaceriaceae”.
Some antibiotics only work on
Gram + or Gram - bacteria.
We measure the diameter of the
zone of inhibition in mm and
look up in Kirby-Bauer
Antibiotic Sensitivity table.
If an organism is not listed in the
table, we report “Cannot be
determined”.
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In this picture, we can see colonies growing in the
zone of inhibition.
Each of these colonies would have to be isolated,
grown in broth, and retested because it is highly
possible that these bacteria are resistant to the
antibiotic.
It would be better to choose an antibiotic with a clear
zone of inhibition.
MIC- Minimum Inhibitory Concentrations are
determined with agar-filled 96 well plates that
have a variety of antibiotics at different
concentrations. The \entire plate is inoculated
with the test organism and is read by a
machine.
MIC is the lowest concentration of antibiotic
that will kill the test organism.