MICR290_Chapter 9_AFernando lecture Audio recording

Chapter 9: Controlling Microbial Growth in the Environment

Introduction to Microbial Control

• Controlling vs. Eliminating Microbes

  • Controlling: Stopping growth, not necessarily killing all microorganisms.

  • Terminology importance:

    • Cidal: Refers to killing the microorganisms completely.

    • Static: Refers to stopping the growth of microorganisms without eliminating them.

Different Terminologies for Microbial Control

• Antisepsis: Reduction of pathogenic organisms, e.g., using alcohol to clean surfaces.

• Aseptic: Creating an environment free of pathogenic organisms.

• Cidal: Act of killing microorganisms.

• De-germing: Mechanical removal of microbes (e.g., washing hands).

• Disinfection: Killing pathogens on non-living surfaces (e.g., tables, tools).

• Pasteurization: Using heat to reduce pathogens, commonly in milk and beverages.

• Sanitation: Removing pathogens to meet public health standards.

• Stasis/Static: Halting growth without killing (e.g., bacteriostatic).

• Sterilization: Complete destruction of all microorganisms on an object.

Key Concepts in Microbial Control

• Understanding distinctions between these terms is crucial for proper microbial management.

Microbial Growth Curve

• Growth curve analysis:

  • Y-axis: Microbial population (log scale).

  • X-axis: Time (minutes).

  • Key observation: 90% of microorganisms can die at a consistent rate over time as nutrients are consumed.

Mechanisms of Action Against Microbes

1. Targeting Cell Structure

   • Disruption of:

     • Cell wall synthesis.

     • Cell membrane integrity.

     • Nucleic acid synthesis.

     • Protein synthesis.

   • Each antimicrobial method targets specific cellular structures.

2. Resistance Levels of Microbes

   • From most resistant to least:

     • Prions > Bacterial endospores > Mycobacteria > Cysts of protozoa > Gram-negative bacteria > Fungi > Gram-positive bacteria > Enveloped viruses.

Factors Affecting Antimicrobial Efficacy

• Site to be treated: Human cells vs. other objects.

• Relative microbial susceptibility and resistance: Classified as high, intermediate, or low efficiency.

Physical Methods of Microbial Control

1. Heat

   • High temperatures disrupt proteins and nucleic acids.

   • Moist Heat: More effective than dry heat (e.g., autoclaving).

     • Boiling effectively kills many pathogens but may not eliminate resilient forms like endospores.

   • Dry Heat: Higher temperatures and longer exposure required.

   • Incineration: Ultimate sterilization method; applicable for disposal of hazardous materials.

2. Cooling Techniques

   • Refrigeration: Slows microbial growth, not effective for all pathogens.

   • Freezing: Can preserve but may not sterilize (psychrophilic microbes can survive).

3. 5rzuJdDesiccation & Lyophilization

   • Desiccation refers to drying out organisms; lyophilization involves removing water for long-term preservation.

4. Filtration

   • Physical removal of microorganisms using barriers like membranes with specific pore sizes.

5. Radiation

   • Using ionizing radiation to damage DNA and kill microbes; effective for sterilizing food and medical equipment.

   • UV light can disinfect surfaces and air.

Chemical Methods of Microbial Control

• Alcohols: Effective against bacteria; commonly used for skin antisepsis.

• Halogens: (e.g., chlorine, iodine) effective as disinfectants.

• Phenols: (e.g., Lysol) effective against bacteria in healthcare settings.

• Oxidizing Agents: (e.g., hydrogen peroxide) disrupt microbial enzymes and DNA.

• Surfactants (Soaps/Detergents): Decrease surface tension, facilitating microbial removal but not directly antimicrobial.

• Formaldehyde and Glutaraldehyde: Used for disinfection, preserving tissues, and controlling microbes in laboratory settings.

Antimicrobial Enzymes and Antibiotics

• Enzymes like lysozyme in tears provide innate defense against bacteria; antibiotics used for treatments.

Biosafety Levels

• Classifications of laboratory safety for handling pathogenic microorganisms:

  • Levels 1-4, with BSL4 being the highest containment level for highly infectious pathogens.

Conclusion

• Understanding microbial control methods and terminology is vital for effective management during infections or contaminated environments. Effective strategies incorporate physical, chemical, and biological approaches to ensure safety and efficacy.