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.