4.4.6 Investigating Microbial Growth

Key Steps in Investigating Microbial Growth

1. Preparation of the Culture Medium

• Use sterile nutrient agar or broth as the growth medium, containing essential nutrients like carbon, nitrogen, and vitamins.

2. Sterilisation

• Sterilise equipment and the medium using an autoclave to prevent contamination from other microbes.

3. Inoculation

• Transfer a small sample of microorganisms onto the growth medium using sterile equipment, such as an inoculating loop or pipette.

4. Incubation

• Place the inoculated medium in an incubator at the optimal temperature for the microorganism (e.g., 37°C for human pathogens). Ensure the conditions are suitable for growth, such as aerobic or anaerobic environments depending on the organism.

5. Observation and Measurement

• Observe microbial growth over time by measuring:
• Colony size on agar plates.
• Turbidity (cloudiness) of broth cultures using a colorimeter to estimate population density.
• Direct cell counts using a haemocytometer or counting colonies.

Key Factors Affecting Microbial Growth

• Temperature: Enzyme activity in microbes is affected by temperature; growth is optimal at an organism's specific temperature range.
• pH: Extreme pH levels can denature microbial enzymes, affecting growth.
• Nutrient Availability: Sufficient nutrients like glucose or amino acids are essential for microbial metabolism and reproduction.
• Oxygen Availability: Aerobic organisms require oxygen, while anaerobes grow in its absence.

Safety Considerations

• Work in a sterile environment to prevent contamination.
• Use aseptic techniques (e.g., flaming inoculating loops and sealing petri dishes).
• Dispose of microbial waste appropriately to avoid environmental contamination.

Applications

• Investigating microbial growth can inform:
  • Food safety by testing microbial contamination in products.
  • Antibiotic resistance studies.
  • Industrial processes like fermentation.