CHAP 8 MPLEC x Lyka

Sterilization and Asepsis

• Sterilization: removal or destruction of all microorganisms and viruses, except prions; some innocuous microbes may remain in environments deemed sterile.

• Commercial sterilization (e.g., canned foods): does not kill all hyperthermophiles; they are not disease-causing and cannot grow at ambient temperatures, so they are of no practical concern.

• Aseptic environment/procedure: free of contamination by pathogens; antisepsis (on living tissue) refers to reducing pathogens on skin/tissues; e.g., skin prep, surgical fields.

Disinfection, Degerming, Sanitation, and Antisepsis

• Disinfection: use of physical/chemical agents to inhibit or destroy microorganisms (pathogens); does not guarantee elimination of all pathogens; endospores and some viruses may survive; effectiveness depends on concentration and contact time.

• Degerming: removal of microbes from a surface by mechanical means (e.g., handwashing, prepping skin for injections).

• Sanitization: reducing the microbial load to meet public health standards; used on utensils, public surfaces; examples include dishwashing in restaurants and public restrooms.

Terminology (Table 9.1) – Key terms and examples

• Antisepsis: reduction of microorganisms on living tissue; examples: iodine or alcohol to prepare skin for injections; antiseptics may also be disinfectants at higher strength.

• Aseptic: environment/procedure free of pathogenic contaminants; standard aseptic techniques.

• -cide / -cidal: destruction of a type of microbe (e.g., bactericide, virucide).

• Degerming: removal of microbes by mechanical means (handwashing, swabbing).

• Disinfection: destruction/inhibition of pathogens on nonliving surfaces; may not kill all microbes.

• Pasteurization: heat treatment to destroy pathogens and reduce spoilage organisms in foods/beverages.

• Sanitization: removal of pathogens from objects to meet public health standards.

• -stasis / -static: inhibition of microbial growth/metabolism without killing; e.g., refrigeration.

• Sterilization: destruction of all microorganisms and viruses on an object.

• Examples and notes:

  • Antisepsis: skin prep with iodine/alcohol; aseptic techniques in clinical settings.

  • -cide / -cidal: bactericide, fungicide, germicide, virucide.

  • Pasteurization: milk, fruit juices, wine, beer; not sterilization.

  • Sanitation standards vary by jurisdiction; germicidal effectiveness depends on context.

Pasteurization and Heat Treatments

• Pasteurization: heat to kill pathogens and reduce spoilage organisms in foods/beverages (e.g., milk, fruit juices, wine, beer); not a sterilization method.

• Ultra-High-Temperature (UHT) sterilization: flash heating to sterilize liquid foods.

• Moist heat vs. dry heat: moist heat denatures proteins and disrupts membranes; dry heat requires higher temperatures for longer times and is less effective on moisture-sensitive items.

Stasis vs. Cide

• -static / -stasis: inhibit growth or metabolism without necessarily killing the microbes; refrigeration is typically bacteriostatic.

• -cide / -cidium: agents that destroy or permanently inactivate a microbe (kills).

Microbial Death Rates

• Microbial death: permanent loss of reproductive ability under ideal conditions.

• Evaluation: microbial death rate is often used to assess antimicrobial efficacy; death rate is usually constant for a given organism under fixed conditions.

Antimicrobial Action – Two main modes

• Disrupt cell walls and cytoplasmic membranes: damage leads to lysis or impaired integrity; viral envelopes aid in attachment and entry.

• Interfere with proteins and nucleic acids: denaturation of enzymes; disruption of replication and metabolism.

Mechanisms: Effects on Cells and Viruses

• Cell walls and membranes: damage compromises osmoregulation; viral envelope disruption prevents replication.

• Proteins and nucleic acids: denaturation or inactivation halts metabolism and reproduction.

The Selection of Microbial Control Methods

• Ideal agent does not exist: needs to be inexpensive, fast-acting, stable during storage.

• No single method is perfect; selection depends on the site, organism, and safety considerations.

Factors Affecting Efficacy of Antimicrobial Methods

• Site to be treated: some methods cannot be used on humans/animals or mucous membranes; instruments may require sterilization if invasive.

• Relative susceptibility of microorganisms: death rate for a given agent is usually constant for a given microbe; enveloped viruses (e.g., HIV) are generally more susceptible than nonenveloped viruses (e.g., polio).

• Biosafety levels: guidelines differ by risk group and setting.

Relative Susceptibility of Microorganisms

• Most resistant to least resistant (summary): Prions → bacterial endospores → protozoan cysts → mycobacteria → protozoan cysts → small nonenveloped viruses → active-stage protozoa → fungal spores → most Gram-negative bacteria → vegetative fungi → large nonenveloped viruses → most Gram-positive bacteria → enveloped viruses → most susceptible.

Prions and Prion Diseases

• Prions: infectious proteins; extremely resistant to standard disinfection; cause degenerative brain diseases in humans and animals; require special decontamination methods.

• Prion diseases: prions trigger abnormal folding of normal proteins in the brain; include human and animal diseases; can be transmitted via infected meat products.

Germicidal Effectiveness for Prions

• High resistance organisms require strong methods to inactivate; prions show very high resistance compared with typical microbes.

• Commonly used high-level methods include specific autoclaving and chemical treatments designed for prions.

Physical and Environmental Conditions

• Temperature and pH: higher temperatures increase germicidal effectiveness; acidic conditions enhance the antimicrobial effect of heat.

• Organic materials (soil, fats, biofilms): interfere with penetration of heat, chemicals, and some radiation; can inactivate certain disinfectants.

Environmental Conditions – Organic Materials and Biofilms

• Biofilms impede penetration of disinfectants and protective matrices shield microbes from treatments.

Biosafety Levels (BSL)

• BSL-1: minimal precautions (handwashing).

• BSL-2: hazardous agents; protection against contaminated objects and sharps.

• BSL-3: HEPA-filtered; controlled access; respiratory protection.

• BSL-4: most secure; sealed airlocks; showers; multiple containment features.

Physical Methods of Microbial Control

• Extreme heat and cold: boiling, autoclaving; pasteurization; ultra-high-temperature sterilization; refrigeration and freezing; desiccation; lyophilization.

• Filtration: physical removal using sieves/filters (e.g., HEPA filters).

• Osmotic pressure: high salt/sugar inhibits metabolism by removing water; fungi tend to tolerate hypertonic conditions better than bacteria.

• Radiation: ionizing (electron beams, gamma rays, some X-rays) vs nonionizing (UV, visible, infrared); UV has antimicrobial energy.

Heat-Related Methods

• Moist heat: denatures proteins and disrupts cytoplasmic membranes.

• Boiling: kills vegetative cells and most viruses within ~10\text{ min} at sea level.

• Autoclaving: steam under pressure; achieves sterilization.

• Pasteurization: heat to destroy pathogens and reduce spoilage organisms (not sterilization).

• Ultra-High-Temperature Sterilization: very high heat for short time to sterilize.

• Dry heat: requires higher temperature and longer exposure; suitable for dry items.

Refrigeration and Freezing

• Refrigeration: 0^
  outine{°C} to 7^
  outine{°C} to slow metabolism and growth.

• Freezing: below 0^
  outine{°C}; water is not available; most microbes cannot grow.

• Note: Listeria and Yersinia can pose risks in refrigerated foods/products.

Desiccation and Lyophilization

• Desiccation: drying preserves foods and inhibits many pathogens.

• Lyophilization: freezing and drying to preserve microbes and cells for long periods.

Filtration

• Filtration: physical separation by pore size; traps microbes larger than pore; smaller microbes pass through.

• HEPA filters: used in operating rooms and rooms with immunocompromised patients to reduce airborne microbes.

Osmotic Pressure

• High salt/sugar environments remove water, inhibiting metabolism; fungi often tolerate hypertonic conditions better than bacteria (e.g., jelly mold growth vs bacteria).

Radiation

• Ionizing radiation: electron beams, gamma rays, X-rays; high-energy, short wavelengths; used to sterilize medical devices.

• Nonionizing radiation: UV, visible, infrared; UV can act as an antimicrobial agent but has limited penetration.

Chemical Methods of Microbial Control

• Categories: Phenolics, Alcohols, Halogens, Oxidizing Agents, Surfactants, Heavy Metals, Aldehydes, Gaseous Agents, Enzymes, Antimicrobial Drugs.

• Phenol and Phenolics: broad-spectrum; used as disinfectants.

• Alcohols: bactericidal, fungicidal, virucidal against enveloped viruses; not effective against spores; denature proteins and disrupt membranes; 70–90% alcohol is most effective; water is needed for protein denaturation.

• Halogens (iodine, chlorine, chlorine dioxide, bromine, fluoride): broad activity; used for skin prep and surface disinfection.

• Oxidizing agents (H2O2, ozone, peracetic acid): strong disinfectants; may sterilize certain equipment.

• Surfactants (soaps/detergents): reduce surface tension and remove microbes; often used in combination with mechanical cleaning.

• Heavy metals (silver, copper): antimicrobial (wound care, surfaces).

• Aldehydes (formalin): high-level sterilants; used in embalming and hospital equipment.

• Gaseous agents (ethylene oxide): sterilants for heat-sensitive equipment; toxic and explosive risks.

• Enzymes and antimicrobial drugs: specialized enzymatic disinfection; targeted action against specific pathogens.

Development of Resistant Microbes

• Extensive use of antimicrobial products can promote resistance in microbes: resistant strains can persist and proliferate after susceptible cells die.

• Pathogens such as M. tuberculosis, Pseudomonas aeruginosa, Escherichia coli, and Staphylococcus aureus have shown reduced susceptibility to common disinfectants/antiseptics.

Quick Quiz Concepts (from the end of the notes)

• Sanitation before sterilization: reduces microbial load to safer levels before more rigorous sterilization steps; lowers risk of infection.

• Temperature as a control factor: higher temperatures generally increase disinfection efficiency; heat can prevent microbial growth and replication.

• Handwashing importance: mechanical removal (degerming) is a key step in reducing transmission.

• Wound cleansing with instruments: use appropriate disinfection method based on invasiveness and contact with mucous membranes.

• Rationale for disinfection choice: based on risk of infection, tissue contact, and potential adverse effects; choose higher-level disinfection for invasive procedures.

• Note on practical application: Always consider site, organism, and safety when selecting a microbial control method.