Ex. 12: Chemical Antimicrobial
Agents: Antibiotics
Objectives ??
Fleming and the Discovery of
Penicillin
 1928
mold grows on
Staphylococcus
aureus plate
 Mold
is named
Penicillium notatum
 Florey
and Chain
isolated Penicillin 10
years later – received
Nobel prize
Vocabulary
 Antibiotics
vs. chemotherapeutic agents
 bacteriostatic
vs. bactericidal
 Commonly
used antibiotics: Penicillin,
Ampicillin, Tetracycline, Vancomycin,
Ciprofloxacin
 Agar
Disk Diffusion Test or Kirby-Bauer
Antimicrobial Susceptibility Test
 Mueller-Hinton
(MH) agar
Day 1
Materials needed per student:
 One Petri plate containing
Mueller-Hinton (MH) agar
 One of the four bacterial
species assigned per table
 Sterile cotton swab
Materials needed per team of
two:
 Laminated white card with
black lines
 Bunsen burner, inoculating
loop
Materials needed per table:
 One 0.5 McFarland standard (contains
~ 1.5 x 108 CFU/ml)
 Four sterile saline tubes
 Four 1 ml sterile pipettes
 Five single disk dispensers plus five
cartridges of antibiotic disks (P, AM, T,
VA, CIP).
 One each of the following pure
cultures:
o E.coli ATCC: 25922
o S. aureus ATCC 25923
o P. aeruginosa,
o S. marcescens
Each student tests all the antibiotics for one bacterial species
How to streak for
confluent growth
Mark the
bottom of
your plate
with a line.
This will be
your #1
position.
Rotate 60º
clockwise
Rotate 30º
clockwise
Review this 5 mins (in-house) movie clip
on how to test for antibiotic susceptibility
with the Kirby Bauer method.
Day 2
Examine each
plate and look
for “zones of
inhibition”.
Measure  of
Zone of
inhibition (in
mm) and record
the value in the
table in the lab
report section