Microbial Growth and Nutrition Lecture Notes

Introduction

• Lecture on microbial growth and nutrition.
• For CCP students: Chapter 6; Camden County students: Chapter 7.
• Considered an easier chapter, not requiring extensive study.

Microbial Growth

• Growth defined as cell division into daughter cells, not size increase.
• Physical Requirements for Growth:
  • Temperature:
    • Most are mesophiles (20-40°C).
    • Psychophiles (below 20°C) and thermophiles (above 42-43°C).
    • Importance of temperature in food safety due to bacterial growth in the "danger zone" (20-40°C).
  • pH:
    • Most bacteria grow at pH 6.5-7.5.
    • Molds and yeasts prefer pH 4-6.
    • Acidophiles, like H. pylori, can grow in acidic environments (e.g., stomach).
  • Osmotic Pressure:
    • Hypertonic environments can cause plasmolysis, inhibiting bacterial growth.
    • Skin, a salty environment, primarily hosts Staphylococcus aureus.

Chemical Requirements for Growth

• Carbon: Structural backbone of organic molecules.
• Nitrogen: Component of proteins, DNA, ATP.
  • Bacteria decompose proteins or use ammonia/nitrate.
• Sulfur: Found in amino acids, thiamine, biotin.
• Phosphorus: Found in DNA, RNA, ATP, and cell membranes.
• Trace Elements: Required in small amounts, act as enzyme cofactors (e.g., iron, copper, zinc).
• Oxygen:
  • Obligate aerobes: Require oxygen.
  • Facultative anaerobes: Use both aerobic/anaerobic conditions.
  • Obligate anaerobes: Cannot tolerate oxygen.
  • Aerotolerant anaerobes: Oxygen is non-lethal.
• Organic Growth Factors: Vitamins, amino acids, purines, pyrimidines.

Culture Media

• Chemically Defined and Complex Media: Defined in previous chapters.
• Reducing Media: Cultivation of anaerobic bacteria, contains chemicals to deplete oxygen.
• Capnophiles: Require high CO2 conditions, ideal in environments like blood.

Biosafety Levels (BSL)

• BSL-1: Basic precautions.
• BSL-2: Lab coat, gloves, eye protection.
• BSL-3: Biosafety cabinet; for airborne microorganisms.
• BSL-4: High risk, requires complete isolation and specialized facilities.

Pure Culture Techniques

• Streak Plate Method: Used for obtaining pure cultures by isolating single colonies.

Bacterial Growth Phases

1. Lag Phase: Adjustment to new environment, activation of metabolic pathways.
2. Log Phase: Exponential cell growth.
3. Stationary Phase: Equilibrium between cell growth and death.
4. Death Phase: Decline in nutrients, cells die and become food for others.

Conclusion

• Chapter is foundational, not overly complex.
• Transition into metabolism and infection topics next.
• Reminder of upcoming exams and preparation needs.