History and Definitions of Microbial Control

History of Microbial control

• Microbial control dates back to the 1500s when Girolamo Fracastoro proposed that "spores" transferred diseases.
• Ignaz Semmelweis promoted handwashing in medical procedures to prevent puerperal fever.
• John Snow studied cholera outbreaks and traced their sources.
• Joseph Lister introduced aseptic surgery practices and used carbolic acid as an antiseptic.
• Louis Pasteur and Robert Koch contributed significantly to the "Golden Age of Microbiology".

Microbial Control: Definitions

• Sterilization: eliminates all living microorganisms.
• Commercial Sterilization: targets Clostridium botulinum endospores in canned food.
• Sanitization: reduces microbial counts to safe levels for public health.
• Disinfection: eliminates vegetative pathogens on inanimate objects.
• Antisepsis: eliminates vegetative pathogens on living tissue.

Microbial Control: Actions of Agents

• Alteration of Membrane Permeability: Microbial control agents can disrupt cell membranes, causing leakage.
• Damage to Proteins and Nucleic Acids: Agents can damage or disrupt protein structure or interfere with DNA/RNA synthesis.

Physical Methods of Microbial Control

• Heat: One of the most common methods of microbial control.

  • Dry Heat Sterilization: Uses high temperatures (148–260°C) for at least 45 minutes to kill spores and vegetative forms. Examples include direct flaming and incineration.
  • Moist Heat Sterilization: More effective than dry heat due to the ability of water to penetrate cells.
    • Boiling: Kills vegetative pathogens, some viruses, and spores within 10 minutes at 100°C.
    • Autoclave: Uses steam under pressure (15 psi) to reach 121°C and kill even endospores in 15-30 minutes.
    • Pasteurization: Uses high temperatures for short durations to eliminate pathogens without affecting food flavor. Two types: HTST (72°C for 15 seconds) and UHT (135°C for 2-5 seconds).
    • Fractional Sterilization: Uses moist heat at 100°C, repeatedly over several days, for vegetative forms and endospores.
      • Tyndallization: Uses free-flowing steam.
      • Inspissation: Uses an oven at 60°C.

• Filtration: Passes liquid or gas through a filter with pores small enough to retain microbes.

  • HEPA Filters: Remove microbes from air.
  • Membrane Filters: Made of nitrocellulose or cellulose acetate, can filter out bacteria, viruses, and large proteins.

• Low Temperature: Slows microbial growth but may not kill them.

  • Refrigeration (0-7°C) inhibits growth.
  • Freezing (subzero temperatures) preserves microbes but doesn't necessarily kill them.

• High Pressure: A non-thermal food preservation technique that kills microorganisms by using high pressure for a set period.

  • HPP (High Pressure Processing) preserves taste, texture, and nutrients.

• Desiccation: Drying out removes water, inhibiting microbial growth.

  • Viruses, bacterial endospores, and protozoal cysts can survive desiccation.

• Osmotic Pressure: High salt or sugar concentrations cause plasmolysis, inhibiting growth.

  • Molds and yeasts tolerate low moisture/high osmotic pressure better than bacteria.

• Radiation: Energy that can damage cells.

  • Ultraviolet (UV) Radiation: Used to reduce airborne contamination. Effectiveness depends on exposure time, intensity, and microbial susceptibility. Has poor penetration.
  • Ionizing Radiation: High energy radiation (gamma rays, beta rays) removes electrons from molecules, killing microorganisms.

Chemical Methods of Microbial control

• Disinfectants: Kill microorganisms on inanimate objects.
  • Phenol and Phenolics: Disrupt cell membranes and denature proteins.
  • Halogens: Oxidize cellular components.
    • Chlorine: Used as a disinfectant in gaseous form (CI2) or compounds.
    • Iodine: Available as a tincture or iodophor.
  • Alcohols: Denature proteins and dissolve lipids.
    • Ethanol (60-90%) and Isopropanol are effective.
  • Heavy Metals and Compounds: Exert oligodynamic action (inhibiting microbial growth in small amounts).
    - Silver, mercury, copper, and zinc are common examples.
  • Surface-Active Agents: Decrease surface tension, aiding in removing microbes.
    • Soaps have limited germicidal activity but help remove microbes.
    • Acid-anionic detergents are used for cleaning dairy equipment.
  • Quaternary Ammonium Compounds (Quats): Cationic detergents that disrupt cell membranes. More effective against gram-positive bacteria.
    • benzalkonium chloride
    • cetylpyridinium chloride
  • Organic Acids and Derivatives: Inhibit fungal metabolism. Used as food preservatives.
    • Sorbic acid, benzoic acid, and propionic acid.
  • Aldehydes: Inactivate proteins. Among the most effective chemical disinfectants.
    • Formaldehyde and glutaraldehyde.
  • Gaseous Chemosterilizers: Penetrate materials and kill all microorganisms.
    • Ethylene oxide is most commonly used.

Explore the significant milestones in microbial control from the 1500s to modern practices. Learn about key figures like Girolamo Fracastoro, Ignaz Semmelweis, and Louis Pasteur, as well as essential definitions like sterilization and disinfection. This quiz will test your knowledge on the history and methods used in controlling microbial growth.