Controlling Microorganisms

Controlling Microorganisms

  • Microbes are ubiquitous but not all are harmful; some are necessary for life.
  • Historically, humans have employed various methods to control microbial threats (e.g., burning corpses, embalming).

Key Outcomes in Microbial Control

Four primary outcomes of microbial control are:

  1. Sterilization:

    • Destroys or removes all viable microorganisms including viruses.
    • Term "sterile" applies strictly to items that have undergone true sterilization (e.g., surgical instruments).
    • Methods include heat (autoclaving) and chemotherapeutic agents.

  2. Disinfection:

    • Destroys vegetative pathogens but not bacterial endospores.
    • Focuses on removing harmful products (toxins).
    • Commonly used in sanitizing equipment (e.g., bleach solutions, boiling).

  3. Decontamination/Sanitization:

    • Cleans items to reduce microbial contamination to safe levels.
    • Crucial for restoring the safety of utensils in food industries (e.g., using soap and commercial dishwashers).

  4. Antisepsis/Degermation:

    • Reduces the microbial load on living tissues (e.g., human skin) often through scrubbing or chemical applications (e.g., alcohol scrubs).

Relative Resistance of Microbial Forms

  • Microbial Resistance Hierarchy: There is a spectrum of microbial resistance levels:
    • Bacterial endospores are the most resistant.
    • Vegetative cells are less resistant than endospores.
    • Viruses have varying resistance; enveloped viruses are generally easier to kill than non-enveloped viruses.
  • Reference table outlines comparative resistance and necessary controls for various microbes.

Prions as Special Cases

  • Prions are highly resistant to typical sterilization methods.
  • Required measures include a combination of heat and chemicals as per CDC guidelines.

Agents vs. Processes

  • Different terms denote either processes (e.g., sterilization, disinfection) or the agents involved (e.g., bactericide).
    • Bactericide: Kills bacteria except for endospores.
    • Fungicide: Kills fungi (spores, hyphae, yeasts).
    • Virucide: Inactivates viruses, especially on living tissues.
    • Germicide/Microbicide: Kills microorganisms.
    • Asepsis: Prevents microbial entry into sterile areas.

Practical Considerations in Microbial Control

  • Device Classification:
    • Critical: Must be sterilized (e.g., syringes).
    • Semicritical: Requires at least high-level disinfection (e.g., endoscopy equipment).
    • Noncritical: Need only low-level disinfection unless contaminated (e.g., blood pressure cuffs).
  • Factors Affecting Control:
    • Microbial load, type, temperature, concentration, and presence of organic matter influence the efficacy of microbicides.

Modes of Action of Antimicrobial Agents

  • Classification of cellular targets affected by antimicrobials:
  1. Cell wall (damaged by detergents and alcohol).
  2. Cytoplasmic membrane (disrupted by surfactants).
  3. Protein synthesis (interfered by formaldehyde, radiation).
  4. Proteins (denatured by heat and chemicals).

Heat as a Method of Control

  • Moist Heat: Generally more effective than dry heat.
  • Common methods:
    • Boiling: Disinfection, not sterilization (30 min at 100°C).
    • Pasteurization: Disinfection of beverages (e.g., milk).
    • Autoclaving: Effective sterilization (e.g., steam under high pressure).
  • Dry Heat: Utilizes higher temperatures for sterilization (e.g., incineration, hot-air ovens for glassware).

The Effects of Cold and Desiccation

  • Cold mainly slows microbial growth (microbistatic) and isn't reliable for disinfection.
  • Lyophilization can preserve cultures effectively.
  • Desiccation can sometimes lead to the survival of certain pathogens.R

Chemical Control Methods

  • There are different levels of chemical decontamination:
    • High-level: Destroys all microbial forms including endospores.
    • Intermediate-level: Kills fungal spores and some pathogens.
    • Low-level: Targets vegetative bacteria and some viruses.
  • Factors such as exposure time, concentration, and material can affect the efficacy of chemical agents.

Learning Outcomes

  • Be able to define critical terms related to microbial control.
  • Compare and contrast the actions of microbicidal and microbistatic agents.
  • Identify the categorization of cellular targets affected by antimicrobial agents.