Control of Microorganisms - Study Guide

Essential Skills Lab 7 - Control of Microorganisms

Reference Guidelines for Disinfection and Sterilization

  • Source: CDC Guidelines for Disinfection and Sterilization in Healthcare Facilities
  • URL: CDC

Overview of Bacterial Growth Prevention

Understanding the requirements for optimal bacterial growth enables effective strategies for preventing contamination. Familiarity with key terms is crucial for evaluating disinfectant products used in clinical settings. Reading and adhering to product instructions is essential, as misuse can result in ineffective results (e.g., diluting products is not always beneficial).

A. Definitions: Sterilization, Disinfection, and Sanitation

1. Sterilization
  • Definition: The complete destruction of all forms of microbial life, including spores. Sterility is absolute; no living organisms can be present.
2. Disinfection
  • Definition: The process that kills vegetative cells, with varying efficacy against spores. Disinfection is not absolute; it may leave some vegetative cells viable. It is mainly aimed at killing vegetative pathogens.
3. Sanitation
  • Definition: A process that reduces the total number of organisms present, essentially thorough cleaning.
4. Asepsis
  • Definition: Techniques used to prevent the introduction of organisms into a particular area.
5. Aseptic Techniques
  • Definition: Methodologies aimed at ensuring no contaminants are introduced into sterile environments.
6. Antisepsis
  • Definition: Prevention of sepsis through the exclusion, destruction, or inhibition of organisms. Antisepsis encompasses a broader range of actions than asepsis.
7. Disinfectant
  • Definition: A chemical agent that kills vegetative cells and is typically used on inanimate objects. The effectiveness of disinfectants is a function of their specific properties and application techniques.
8. Antiseptic
  • Definition: A chemical agent that may kill some organisms and inhibits the growth of others. Antiseptics are used on living tissue.
9. Sanitizer
  • Definition: A chemical agent that reduces the total number of organisms present on surfaces.
10. Static vs. Cidal
  • Static: Terms that end in 'static' indicate the inhibition of organism growth (e.g., bacteriostatic).
  • Cidal: Words ending in 'cidal' indicate the killing of organisms (e.g., bacteriocidal).
11. Quenching
  • Definition: The neutralization of chemical agents by the presence of organic or biological substances (e.g., blood, pus).
12. Fomite
  • Definition: An inanimate article that can transmit infectious agents—this term applies to items like sheets, books, food containers, etc.

B. Factors Affecting Efficacy

To choose appropriate disinfection and sterilization methods, several parameters must be assessed:

1. Desired Outcome
  • Sterility: Required for invasive techniques and surgical environments.
  • Disinfection: Use when sterility is not required but there is a risk of pathogens.
  • Sanitation: Applicable when no pathogens are suspected.
2. Numbers and Locations of Organisms
  • The greater the number of organisms present, the longer the required exposure time for effective sterilization or disinfection.
  • Complex instruments must be dismantled for thorough cleaning as organisms can hide in crevices. The presence of biological material can lead to quenching, compromising disinfection efforts.
3. Innate Resistance of Organisms
  • Variability in susceptibility of organisms affects the effectiveness of disinfection/sanitation methods. Fastidious organisms are typically more sensitive, while other resistant organisms (like Pseudomonas sp., certain viruses, and spore formers) can lead to nosocomial infections.
4. Presence of Organic and Biological Substances
  • Organic materials can shield organisms from disinfectants (quenching). For instance, wounds must be cleaned of debris before applying antibiotics, or the presence of organic matter must be treated before disinfection.
5. Nature of Material to be Processed
  • Non-heat stable materials may not be able to withstand sterilization; thus, appropriate methods must be chosen. For example, heat labile materials like certain plastics and biologicals should be treated with caution.
6. Properties of Processing Agent
  • Concentration: Must be adequately diluted to be effective; too concentrated products may lose efficiency.
  • Persistence: Some chemicals leave residues that can be beneficial in certain contexts.
  • Physical/Chemical Factors: Factors like temperature, pH, and water hardness can affect the effectiveness of disinfectants. For instance, a higher pH may increase antimicrobial activity for some agents.
7. Biofilms
  • Biofilms contain microbial communities that exhibit resistance to standard disinfections, necessitating special considerations in cleaning practices.

C. Physical Methods of Microbial Control

1. Moist Heat
Steam Autoclave
  • Principle: Kills organisms by denaturing proteins; superior to dry heat due to better heat transfer at lower temperatures.
Temperature and Pressure
  • Standard steam sterilization occurs at 121°C under 103.5 kilopascals (15 psi) for 15 minutes.
  • At lower pressure, effective temperatures drop (e.g., 112°C if half the air remains).
Exhaust
  • Types of exhaust: fast and slow, with specific uses depending on the materials being autoclaved.
Wrappings
  • Sterile materials must be suitably wrapped to protect from the external environment and allow steam penetration. Steri-peel® is a common wrapping material used.
2. Dry Heat
Mechanism
  • Kills organisms by oxidizing cellular components, requiring higher temperatures than moist heat to achieve sterility.
3. Filtration
Membrane Filtration
  • Removes bacteria but allows viruses and toxins to pass through warm liquids such as antibiotic media.
4. Radiation
Ultraviolet Radiation
  • Effective for surface sterilization; however, dangerous to human health (burns, cancers).
Ionizing Radiation
  • Utilized for sterilizing medical equipment and plastics. Research into its efficacy for food treatment continues.
5. Sonication
  • Uses high-frequency sound waves to clean materials, helpful for intricate objects like surgical tools.
6. Low Temperatures
  • Used to preserve microorganisms, as cold temperatures can limit metabolic activities of microorganisms (not killing them).

D. Chemical Methods of Microbial Control

The selection of disinfectants depends on the risk associated with the equipment used:

1. Critical Items
  • Require complete sterility, such as surgical instruments, due to the high risk of infection upon contamination.
2. Semicritical Items
  • In contact with mucous membranes, requiring high-level disinfection; examples include endoscopes.
3. Noncritical Items
  • Contact skin without mucous membranes; can be sanitized with low-level disinfectants like mops, which need to be well-maintained to avoid cross-contamination.
Examples of Chemical Agents:
  • Glutaraldehyde: High-level disinfectant when activated. Targeted exposure time for sterilization varies; must be buffered to appropriate pH.
  • Formaldehyde: Similar effects to glutaraldehyde but limited in use due to toxicity.
  • Alcohols: Effective within an aqueous range of 60-90% alcohol for microbial action.
  • Chlorine Compounds: Effective against various microorganisms; however, they can be corrosive and produce harmful gases when misused.
  • Quaternary Ammonium Compounds: Effective against gram-positive bacteria but susceptible to organic matter.

E. Strategies for Nosocomial Infection Prevention

  • Hand Hygiene and proper isolation techniques play key roles. The preferred method for visible soil removal is washing with soap and water. For non-visible contamination, alcohol-based rubs are effective.
Source Isolation
  • Used for highly infectious cases to protect medical staff and other patients by requiring the use of protective clothing, separate room settings, and strict hygiene processes.
Reverse Isolation
  • Protects immunocompromised patients from external germs by using sterilized equipment and clothing.

F. Biosafety Levels

Biosafety levels (1 to 4) reflect the risk associated with handling infectious materials:

Level 1
  • Basic standard practices without specialized equipment.
Level 2
  • Introduces limited access and protective gear such as gloves.
Level 3
  • Requires specialized clothing and controlled access, uses of safety cabinets.
Level 4
  • Maximum containment to handle dangerous pathogens with strict protocols.

G. Containment Equipment

Biological Safety Cabinets
  • Class II: Protects the user and the work area while allowing airflow.
  • Class III: High containment for working with pathogens, typically sealed with a separate exhaust.

H. Personal Protection Devices

  • Mandatory protective clothing such as gloves, face shields, and lab coats must be worn when dealing with hazardous materials.

I. Conclusion

Adhering to these principles and practices helps in the combat against microbial transmission within healthcare settings and fosters a safer environment for both patients and healthcare workers.