Notes on Temperature's Effect on Microbial Growth

Experiment Overview

• Day 1: Setup Day
  • Experiment focuses on the effect of temperature on microbial growth.
  • Conducted in groups of four.

Materials Needed

• Temperature Broths:
  • 15 yellow-capped nutrient agar broths (for Pseudomonas fluorescens, Serratia marcescens, E. coli)
  • 5 clear-capped broths (for Bacillus sterothermophilus)

Procedure

1. Labeling Tubes:
   • Label with organism names, initials, and temperature.
   • Example: Pseudomonas fluorescens labeled as "PF - Initials - Temperature".
2. Inoculation:
   • Inoculate all five tubes with the respective organism.
3. Temperature Setup:
   • Place inoculated tubes at the following temperatures:
     • 5°C (Refrigerator)
     • 25°C (Room Temperature)
     • 38°C (Human Body Temperature)
     • 42°C
     • 55°C

Day 2: Reading Results

• Reading and Analyzing Data:
  • Observe turbidity (cloudiness) in the tubes as an indicator of microbial growth.
  • Compare growth at different temperatures.

Microbial Growth Categories

1. Psychrophiles

• Description: Cold lovers.
• Growth Range: -5°C to 15°C.
• Optimal Growth: Around refrigeration temperatures.

2. Psychrotrophs

• Description: Prefer cold but can grow at warmer temperatures.
• Growth Range: 0°C to just below human body temperature.
• Optimal Growth: Around room temperature.

3. Mesophiles

• Description: Moderate temperature lovers.
• Growth Range: 15°C to 45°C.
• Optimal Growth: Around human body temperature (37°C).

4. Thermophiles

• Description: Heat lovers.
• Growth Range: 42°C to nearly 80°C.
• Optimal Growth: Around 60°C.

5. Extreme Thermophiles

• Description: Thrive in extremely high temperatures.
• Growth Range: 65°C to 110°C.
• Optimal Growth: Close to boiling (90°C - 100°C).

Observations and Results

Pseudomonas fluorescens

• Growth at Temperatures:
  • High turbidity at 5°C and 25°C.
  • No growth at 38°C, 42°C, and 55°C.
• Classification: Psychrotroph.

Serratia marcescens

• Growth at Temperatures:
  • High turbidity at 25°C and 38°C.
  • No growth at 5°C, 42°C, and 55°C.
• Classification: Mesophile.
• Note: Produces red pigment at room temperature (25°C).

E. coli

• Growth at Temperatures:
  • Optimal growth at 38°C (human body temperature).
  • Moderate growth at 25°C and 42°C; no growth at 5°C and 55°C.
• Classification: Mesophile.

Bacillus sterothermophilus

• Growth at Temperatures:
  • Only growth observed at 55°C.
• Classification: Thermophile.

Autoclave and Steam Sterilization

• Purpose: Ensure sterilization of media and instruments.
• Minimum Conditions for Sterilization:
  • 120°C for 15 minutes at 15 psi.

Killed Ampule Test

• Contains Bacillus sterothermophilus endospores (heat-resistant).
• Indications:
  • Yellow in Color: Indicates survival of endospores, meaning sterilization failed.
  • Purple in Color: Indicates successful sterilization (endospores killed).

Additional Testing Indicators

• Use of indicators like bromocresol purple to identify pH changes during fermentation as a result of microbial growth after incubation.

Conclusion

• Understanding the temperature preferences of microorganisms is crucial for studying their growth and implications in health and disease.