Download Labs 13 & 14 - Lone Star College System

Lab 13
Microbial Control with Chemical Agents
1
2
3
4
Do all disinfectants and antiseptics work
equally well against all bacteria?
Answer: No. Some work better against Gramnegative or Gram-positive bacteria and very little
works against Pseudomonas aeruginosa!
1 = 5% phenol
2 - 4 various disinfectants/antiseptics
Zones of inhibition
Escherichia coli
Note the
satellite
colonies
within this
zone of
inhibition.
What does
their
presence
indicate?
No zone
of
inhibition
Staphylococcus
aureus
Answer: Individuals of the population are already resistant to the chemical.
Measuring the size of the zones of inhibition (in mm) is meaningful only
if test substances have been calibrated for concentration, such as
Kirby-Bauer testing of antibiotics.
The colony of Penicillium fungus produced an antibiotic
that inhibited growth of Staphylococcus aureus.
Kirby-Bauer test. Which of the 7 antibiotics tested
would you use to treat an infection caused by the test
organism?
Answer: E, B, G, or D