Microbial Control: Sterilization Methods

Microbial Control: Sterilization, Disinfection, and Antisepsis

• The main purpose of sterilization, disinfection, and antisepsis is controlling infections.
• Sterilization eliminates all forms of microbial life, including spores. This is achieved through methods like gas vapor, physical, or chemical sterilants. It aims to preserve treated products safely at room temperature.
• Physical sterilants include flaming, steam under pressure, filtration, ultraviolet radiation, and ionizing radiation.
• Chemical sterilants include per acetic acid and glutaraldehyde.
• Gas vapor sterilants include ethylene oxide, formaldehyde, hydrogen peroxide vapor, and plasma gas.
• Boiling is an inefficient method of sterilization as it only kills vegetative organisms at 100°C. Spores remain viable.
• Chemical methods of sterilization include ethylene oxide, formaldehyde, hydrogen peroxide vapor, and plasma gas.
• Ethylene oxide gas is used to sterilize sensitive items like catheters, plastic packaging, and equipment with integrated electronics.
• Plasma gas sterilization effectively destroys microorganisms' components, like enzymes, nucleic acids, and DNA.
• Chemical sterilization in an automated machine is used for medical, surgical, and dental instruments (e.g., endoscopes, bronchoscopes). Aldehydes (e.g., glutaraldehyde) are used to sterilize surgical instruments.

Disinfection

• Disinfectants destroy microorganisms living on non-living objects.
• Disinfection is less effective than sterilization, as it does not necessarily kill all microorganisms, especially resistant bacterial spores.
• Disinfection aims to make surfaces free of disease-causing microorganisms.
• Disinfectant levels vary: high, intermediate, and low.
• High-level disinfectants treat items that can't withstand sterilization (e.g., surgical equipment with plastic components). Examples include moist heat and chemicals like glutaraldehyde, hydrogen peroxide, and peracetic acid and chlorine compounds.
• Intermediate-level disinfectants are used where contamination with bacterial spores is unlikely. Examples include alcohols, iodophor compounds, and phenolic compounds (e.g., phenol, carbolic acid). They're used on semi-critical instruments like flexible fiber optic endoscopes, laryngoscopes, vaginal specula, and anesthetic breathing circuits.
• Low-level disinfectants treat non-critical instruments and devices (e.g., blood pressure cuffs, electrocardiogram electrodes, and stethoscopes). Quaternary ammonium compounds are an example.

Antisepsis

• Antiseptics reduce the number of microbes on living tissue, unlike disinfectants which act on non-living surfaces.
• They aim to reduce the possibility of infection or sepsis on living tissues.
• No sporicidal action is involved.
• Selected antiseptic agents include alcohols (e.g., 70-90% ethanol and isopropyl alcohol), iodophors (e.g., betadine), chlorhexidine, and triclosan.
• Alcohol is effective against most organisms except spores. However, it has the disadvantage of being drying to the skin and being inactivated by organic matter.