www.glencoe.com/sites/common_assets/science/virtual_labs/LS08/LS08.html

Scientific Concepts / Phenomena Presented

Bacterial Culture on Agar

• Growing bacteria on nutrient agar in a Petri dish.

Antibacterial / Antimicrobial Testing via “Zones of Inhibition”

• Place sterile paper discs soaked with different substances onto inoculated agar.
• After incubation, observe clear areas (zones) where bacterial growth is inhibited.
• Use a ruler to measure the diameter of each zone of inhibition.

Antibiotics and Mechanisms of Action

• Penicillin
  • Described as the first antibiotic.
  • Produced by an airborne mold.
  • Inhibits growth of certain bacteria, notably those associated with:
    • Strep throat
    • Some pneumonias
    • Bacterial meningitis
• Amoxicillin
  • Presented as derived after penicillin.
  • Has a broader spectrum.
  • Better absorbed by the stomach.
• Erythromycin
  • Described as newer.
  • Inhibits protein production by acting on ribosomes, preventing formation of proteins needed for bacterial cellular processes.

Non-Antibiotic Antimicrobials / Disinfectants

• Household bleach (chlorine bleach): described as having strong antibacterial properties.
• Antibacterial soap: included as a disinfectant category in the experiment.
• Lysol / household disinfectant: listed as another tested solution.

Bacterial Species Included (Test Organisms)

• Staphylococcus aureus
  • Associated with infections in humans/animals, including food poisoning, toxic shock, and cow mastitis (infection linked to milk duct blockage).
• Haemophilus influenza (as named in subtitles)
  • Associated with ear infections and bacterial meningitis.
• Streptococcus pneumonia (as named in subtitles)
  • Associated with pneumococcal pneumonia.

Experimental Biology Workflow

• Inoculate plates with each bacterial species separately.
• Apply discs in consistent locations for comparability.
• Incubate (stated as 24 hours), then measure inhibition zones.

---

Experimental Method (Outlined)

• Prepare nutrient agar Petri dishes.
• Inoculate the agar surface with one bacterial species at a time:
  • Staphylococcus aureus
  • Haemophilus influenza
  • Streptococcus pneumonia
• Place sterile paper discs on the agar, including:
  • Control disc: sterile paper disc with no substance
  • Discs soaked with:
    • Antibacterial soap
    • Household bleach
    • Household disinfectant (e.g., Lysol)
    • Penicillin
    • Amoxicillin
    • Erythromycin
• Incubate the plates for 24 hours.
• Measure zones of inhibition:
  • Identify clear/no-growth rings or areas.
  • Measure the diameter (widest point) with a ruler.
  • Record results in a table for subsequent analysis.

---

Researchers / Sources Featured

• No specific researchers or institutions are named in the subtitles.
• Antibiotics are attributed in general terms:
  • Penicillin: described as “discovered” from an airborne mold (no individual researcher named).