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Sterilization & Disinfection:
- To prevent transmission of microbes to patients. HAVE to follow standard precautions that should be used in interaction with all patients:
- Hand hygiene.
- Respiratory hygiene and cough etiquette.
- Safe injection practices.
- Proper disposal of needles and scalpels. Use of personal protective equipment (PPE) such as masks or face shields, gloves, gowns, and protective eyewear, if dealing with body fluids or exposed to aerosols
- Avoid bacterial transmission (contact, droplet, and airborne).
Infection Control Precautions and Practices
Type of Precaution Type of Patient or Type of Infection Important Precaution Practice Employed Standard All patients Hand hygiene Respiratory hygiene and cough etiquette Safe injection practices Proper disposal of needles and scalpels Standard If exposure to blood, secretions, or body fluids is likely to occur Personal protective equipment (PPE) such as mask, face shield, goggles, gloves, or gown
. (lab-coat)
PRINCIPLES OF STERILIZATION & DISINFECTION
Sterilization: is the killing or removal of all microorganisms,
including bacterial spores.
- Sterilization is usually carried out by autoclaving, (steam
at 121°C under a pressure of 15 lb/in
2
for 15 minutes).
- Heat sensitive instruments/tools are usually sterilized by
exposure to ethylene oxide gas (low temperature use).
- Solutions are sterilized by filtration.
In Disinfection some organisms and bacterial spores may survive. Different disinfectants could be used:
- Corrosive phenol-containing compounds (toxic),
- Ethanol and iodine, which can be used on skin surfaces.
Antiseptics chemicals are used to kill microorganisms on
the surface of skin and mucous membranes.
Clinical Use Commonly Used Disinfectant or Method of Sterilization Sterilize surgical instruments and heat- sensitive materials (e.g., endoscopes, respiratory therapy equipment) Ethylene oxide or glutaraldehyde Sterilize non–heat-sensitive materials (e.g., surgical gowns, drapes) Autoclave Sterilize intravenous solutions Filtration Disinfect air in operating room (when not in use) Ultraviolet light Disinfect floor of operating room Benzalkonium chloride (Lysol) Disinfect stethoscope 70% ethanol Preservative in vaccines Thimerosal
RATE OF KILLING OF MICROORGANISMS
Death of microorganisms occurs at a certain rate dependent primarily on two variables: 1- The concentration of the killing agent 2- The length of time the agent is applied. The rate of killing is defined by the relationship N ∝ 1/ CT Number of survivors= N , Concentration of the agent= C , Time of application of the agent= T.
Disinfectants that are more effective than phenol have a coefficient greater than 1; those that are less effective have a coefficient less than 1.
Chemicals induce bacterial killing by:
(1) disruption of the lipid-containing cell membrane,
(2) modification of proteins,
(3) modification of DNA.
- The 100% isopropyl alcohol coagulates the proteins instantly by creating a protein layer that protects the other proteins from further coagulation.
- While 70% isopropyl alcohol solution penetrates in the cell wall at slower rate and coagulates all protein of the cell wall and microorganism dies. Extra water content slows evaporation, therefore increasing surface contact time and enhancing effectiveness.
- ( Staphylococcus aureus killed in less than 10 seconds with a 50% Isopropyl Alcohol solution and was not killed in 2 hours with a 90% solution: emphasizing the importance of water in killing microorganisms (Tainter et al., 1944))
Detergents:
Detergents are “surface-active” agents composed of a long- chain, lipid-soluble, hydrophobic portion and a polar hydrophilic group, which can be a cation, an anion, or a nonionic group. These surfactants disrupt the membrane. Quaternary ammonium compounds (e.g., benzalkonium chloride) are cationic detergents widely used for skin antisepsis. Benzalkonium chloride is the active ingredient in Lysol (commercial name: kills 99.9%!!!!!!), a commonly used disinfectant for floors and other surfaces.
Phenols:
- Phenol was the first disinfectant used in the operating room (by Lister in the 1860s), it is rarely used, because it is too caustic /corrosive (cause burns). Chlorhexidine is a chlorinated phenol that is widely used as a hand disinfectant prior to surgery (“surgical scrub”) and in the cleansing of wounds. Remains effective for 6 hours ,it binds with the skin. Hexachlorophene, which is a biphenol with six chlorine atoms, is used in germicidal soaps, (could cause neurotoxicity). Phenols not only damage membranes, but also denature proteins.
