1. 22 –Bacteriostatic Compounds, and Antibiotic Resistance
Dr. Souki
Principles & Applications of Microbiology
Cerritos College

2. The Inhibitory Action of Antiseptics and Disinfectants

3. Purpose
To determine the effects of known disinfectants and antiseptics on bacterial growth.

4. FDA-Approved Antiseptics
Tincture of Iodine
2% free iodine
Povidone-iodine
Betadine
E-Z Scrub
Silver sulfadiazine
Creams, wound dressing

5. Common Disinfectants Bleach Ethanol or isopropanol
1:10 dilution household bleach
ppm hypochlorite ion
Biocidal on most vegetative bacteria in seconds
Inactivates most endospores in under 10 minutes
Ethanol or isopropanol
70%
Biocidal
Does not inactivate endospores

6. Procedure Prepare nutrient agar plates Staphylococcus aureus
Escherichia coli
Mark quadrants on plate bottom
Use sterile swab to inoculate
Heat-sterilize forceps
Dip disk in solution
Solution 1:______
Solution 2: ______
Solution 3: ______
Solution 4: ______
Drop disk in center of quadrant
Incubate RT, 48 hours
Measure zone of inhibition

7. How is a zone of inhibition measured?
Measure the diameter of the disk
Measure the diameter of the zone of inhibition

8. Diameters of Zones of Inhibition (mm)
Results
Organism
Diameters of Zones of Inhibition (mm)
Solution 1
Solution 2
Solution 3
Solution 4
Staphylococcus aureus
Escherichia coli

9. The Effects of UV Light on Bacterial Growth

10. Purpose
To determine the effects of UV light on bacterial growth.

11. What is Ultraviolet Radiation
UV penetrates cells and damages DNA

12. Procedure Work as a table. Obtain 1 NA plate.
Prepare 1 plates of either
Bacillus megaterium
Escherichia coli
Inoculate using sterile swab
Expose half the plate, using index card, with lid open to UV light for prescribed amount time
Incubate 37 C, 24 hours
Count colonies

13. Results Table UV Exposure (sec) # Colonies 1 15 3 30 5 60 7 90 Table
B. megaterium
Table
UV Exposure (sec)
# Colonies 1 15 3 30 5 60 7 90
E. coli
Table
UV Exposure (sec)
# Colonies 2 15 4 30 6 60 8 90

14. Detection of Antibiotic Resistance

15. Purpose
To determine the if various bacterial cultures are antibiotic resistant, using the Kirby-Bauer disk-diffusion method.

16. Kirby-Bauer Disk Diffusion Method
Antibiotic
Bactericidal or bacteriostatic
Penicillium (fungus)
First source of penicillin
Alexander Fleming
Beta-lactam antibiotic
Resistance due to beta-lactamases
Inhibits cell wall synthesis in G+ & G-

17. Procedure Work in pairs. Obtain 2 NA plate. Prepare 2 plates
Escherichia coli
Bacillus megaterium
Proteus vulgaris
Staphylococcus aureus
Pseudomonas aeruginosa
Inoculate using sterile swab
Apply antibiotic discs
Incubate 37 C, 24 hours
Measure zone of inhibition

18. Results Collect class data. P. vulgaris S. aureus E. coli
B. megaterium P C Te S
Data set 1
Data set 2
Ave Zone (mm)
Susceptibility
Key:
P = Penicillin 10 ug
C = Chloramphenicol 30 ug
Te = Tetracycline 30 ug
S = Streptomycin 10 ug
Susceptibility:
S = Susceptible
I = Intermediate
R = Resistant

19. Procedure Use the data you collected to determine if the bacteria are:
Resistant
Intermediate
Susceptible