lesson 12

Lesson 12 – Control of Microbial Growth and Antimicrobial Drugs

Introduction

  • Focus: Physical and chemical methods to control microbial growth.
  • Important considerations:
    • Type of microbe
    • Purpose of control: e.g., food safety vs. surgical environments.

Mechanisms of Antibacterial and Antimicrobial Drugs

  • Chemotherapy has ancient roots in treating microbial disease.
    • Ancient use of Tetracycline and Ehrlich’s arsenic compound for syphilis.
    • Development of synthetic drugs (e.g., sulfanilamide).
    • Discovery of natural antibiotics like Penicillin and other natural drugs from fungi and Actinobacteria.
  • Definitions:
    • Antibiotics: Compounds that can kill or inhibit the growth of bacteria.
  • Antibiotics can be:
    • Narrow-spectrum: Effective against a specific range of bacteria.
    • Broad-spectrum: Effective against a wide range of bacteria.
  • Examples of drug mechanisms:
    • Penicillin: Attacks bacterial cell walls.
    • Ciprofloxacin: Inhibits DNA synthesis.
  • Treatment of eukaryotic pathogens (fungi, protozoa, helminths) is more complex:
    • Fungi: Target ergosterol synthesis, as fungal membranes contain ergosterols instead of cholesterol.
    • Protozoa: Target metabolism and DNA synthesis.
    • Helminths: Target their nervous system and metabolic processes.
    • Viruses: Use mechanisms that block nucleic acid synthesis, viral uncoating, and release.

Drug Resistance

  • Causes of antibiotic resistance:
    • Overuse and misuse of antibiotics (e.g., incorrect dosing, incomplete courses).
  • Resistance mechanisms include:
    • Enzymatic degradation (e.g., β-lactamase, carbapenemase).
    • Structural changes in bacteria (e.g., altered membranes).
  • Multi-drug resistant microbes:
    • ESKAPE pathogens are notable for their resistance.

Effectiveness of Antimicrobials

  • Factors determining antimicrobial effectiveness:
    • Microbial type
    • Type of antimicrobial agent used.

Lesson Objectives

  1. Describe key terms associated with microbial control.
  2. Compare physical methods of controlling microbial growth.
  3. Compare various chemicals used for microbial control (uses, advantages, disadvantages, etc.).
  4. Compare methods for testing antiseptics and disinfectants.
  5. Compare natural, semisynthetic, and synthetic antimicrobial drugs.
  6. Describe the development of antimicrobial drugs and key individuals involved.
  7. Outline factors to consider in antimicrobial therapy.
  8. Summarize the five actions of antibacterial drugs with examples.
  9. Explain modes of action of drugs against fungi, protozoa, helminths, and viruses.
  10. Explain drug resistance in microorganisms.

Readings

  • Chapter 13: Control of Microbial Growth
  • Chapter 14: Antimicrobial Drugs

Connecting Your Learning

  • Most microbes are harmless, some cause disease (termed germs).
  • Germ theory of disease: Microscopic organisms can cause disease.
  • When assessing product efficacy (e.g., claims of killing 99% of germs), label interpretation is critical as it may not target the intended microbe.
  • Issues with indiscriminate use of antimicrobial agents, such as hand sanitizers.

Controlling Microbial Growth

  • Pathogenic microbes include protozoa, fungi, bacteria, helminths, and viruses, with a focus on bacterial and viral infections.
  • Infection vs. Disease
    • Infection: Colonization by microbial population.
    • Disease: Damage to host cells through infection.
  • Optimal conditions for microbial growth: Temperature, pH, osmotic pressure.
  • Temperature specifics:
    • Most disease-causing bacteria are mesophilic, growing best at human body temperature.

Heat as a Control Method

  • Effects of heat on cells include protein denaturation.
  • Types of heat treatments:
    • Bactericidal: Kills bacteria.
    • Bacteriostatic: Inhibits bacterial growth.
  • Sterilization vs. Sanitization
    • Sanitization: Reduces microbial populations to safe levels (e.g., dishwashers).
    • Pasteurization: Kills pathogens without nutrient loss (e.g., in milk).

Food Preservation Methods

  • Freezing: Inhibits growth but does not kill bacteria.
  • Osmotic pressure: High salt/sugar concentrations suppress microbial growth.
  • pH alteration: Addition of acids lowers pH, inhibiting non-acidophilic microbes (e.g., lemon juice)
  • Chemical preservatives (e.g., nitrites): Risks of carcinogenic effects.

Preventing Nosocomial Infections

  • Essential sterilization of surgical tools (e.g., autoclave: 121°C).
  • Surgical scrubs & antiseptics aim to reduce skin microbiota before procedures.

Antibiotic Sensitivity Tests

  • Importance of knowing microbial sensitivity for effective treatment.
  • Understanding the implications of antibiotic resistance and the need for selective toxicity in treatment.

Assessment of Resistance Factors

  • Bacteria can be seen using a Kirby-Bauer disk diffusion test or antibiotic sensitivity tests.
  • Recognizing that certain methods of assessment are more effective for understanding bacterial resistance fleets.

Conclusion

  • Regular controls and learning about various methods of microbial control help maintain health and safety standards, particularly in healthcare and food preparation environments. Further discussions would delve into complex interactions between innate and adaptive immune responses.