Article 1: Sterilization, Disinfection, and Antisepsis Flashcards
___ of hospital-acquired infections (HAI) are preventable
1/3
Primary vs Secondary HAI’s
Primary = direct bacterial entry into the bloodstream
Secondary = spready from elswhere in the body
What two bacteria have seen a rise in incidences since the development of powerful broad spectrums antibiotics and increasingly invasive procedures?
- Antibiotic-resistant gram positive bacteria
2. Multi-drug resistant gram negative bacteria
Define Sterilization
Total destruction or physical removal of all microorganisms including the more resistant forms like bacterial spores, mycobacteria, non-enveloped viruses, and fungi
What are the four key sterilizing methods?
Moist heat, Dry heat, Ethylene oxide gas, and Irradiation
Moist Heat
- Saturated steam under pressure, as in an autoclave (121-132 degrees C for 15+ minutes)
- Most widely used and dependable method
- Nontoxic, inexpensive, rapidly kills bacteria and spores
- Prions can be killed by boiling in 1 N NaOH for 10 minutes followed by autoclaving
- Kills microbes by irreversibly denaturing proteins, causing single strand DNA breaks, and compromising membrane integrity
- **Moist heat should be used on all heat- and moist-resistant critical and semi-critical items
Is boiling a method of sterilization?
No; it is a method of DISINFECTION
Dry Heat
- Oven (1 hour at 170 C, 2 hours at 160 C, or 3 hours at 150 C)
- Kills spores but MAY NOT ELIMINATE PYROGENS (fever-inducing agents)
- Only used for materials that can be damaged by moist heat or where moist heat cannot penetrate (e.g. powders, petroleum products, and sharp instruments)
- Nontoxic and does not harm the environment; it penetrates materials and is non-corrosive for metals and sharp instruments
- Kills microbes by irreversibly denaturing proteins, causing single strand DNA breaks and compromising membrane integrity
Ethylene Oxide Gas
o Used for heat- and moisture-sensitive medical devices without deleterious effects on the material used
o Colorless gas that is also highly toxic, flammable and explosive
o Absorbed toxic or mutagenic by-products must be allowed to dissipate by aeration of the materials
o Kills by ALKYLATING PROTEIN, DNA and RNA within cells, which prevents normal cellular metabolism and replication
Irradiation
o UV irradiation – used in laboratory safety cabinets, hospital operating rooms, ionizing, prevention of growth in water in apparatus like the auto-analyzers; INEFFICIENT AS A STERILANT; use limited due to potential for damage to the cornea and skin.
o Ionizing radiations (Gamma rays) u
Used to sterilize heat-sensitive, pre-packed, single use plastic items, including syringes and catheters
Kills by eliciting DNA damage through production of free radical; blocks microbial replication
Disinfection
Removing or killing MOST, but not all, viable organisms (most resilient organisms like mycobacteria, viruses, fungi, and bacterial spores may survive)
Disinfection: High- vs Intermediate- vs Low-level
High-level: can approach sterilization in effectiveness in that it can destroy all microorganisms except large numbers of bacterial spores. For this reason high-level disinfection is oftentimes confused and used interchangeably with sterilization
Intermediate-level: can kill mycobacteria, bacteria, most viruses, most fungi but are not very effective against bacterial spores.
Low-level: can kill most vegetative bacteria, some fungi and some viruses in a reasonable period of time.
Important Qualities of Disinfectants
Antimicrobial activity Solubility Stability Penetration Non-toxicity to humans Non-corrosive Non-staining Deodorizing ability Detergent Capability and Availability
High Level Disinfectants: Characteristics
o Used for all such devices that cannot be sterilized such as endoscopes and plastic surgical instruments that are used in invasive procedures and come into contact with tissues or blood (critical items)
o Most effective if the instruments are clean of all organic matter
o Use approaches sterilization and may kill spores (a few discussed in the sterilization section above).
High Level Disinfectants: Examples
Glutaraldehyde, Oxidizing Agents (Peracetic Acid, Hydrogen Peroxide, and Chlorine Compounds [e.g. bleach])
Mnemonic: “GO High” for most effective disinfectants
Intermediate Level Disinfectants: Characteristics
o Used on semi-critical instruments, which are unlikely to be contaminated with bacterial spores or resistant organisms (e.g. laryngoscopes, endoscopes, vaginal specula, anesthesia breathing circuits, etc…) These instruments come into contact with mucus membrane or non-intact skin.
o Spores are not killed by intermediate level disinfectants
Intermediate Level Disinfectants: Examples
Alcohols, Iodine-Containing Compounds (Iodophors), and Phenolic Compounds
Low Level Disinfectants: Characteristics and Example
o e.g. Quaternary Ammonium compounds are used to clean non-critical instruments such as stethoscopes, blood pressure cuffs, and electrocardiogram electrodes.
o Even though these instruments come into contact with patients, they contact only intact skin and do not penetrate through mucosal layer or into sterile tissue.
o Many organisms survive treatment using low level disinfectants
Antisepsis
Disinfectants used to LOWER the number of microorganisms on skin surfaces
***DO NOT kill bacterial spores but are VERY EFFICACIOUS against VEGETATIVE BACTERIA and VERY SAFE
Antiseptic Compounds
Phenolic Compounds Iodine-Containing Solutions Chlorhexidine Alcohols (Ethanol and Isopropanol) Quaternary Ammonium Compounds Triclosan
Mnemonic: “PIC A QT”
Alcohols (Ethanol and Isopropanol)
o Kill most microbes (including mycobacteria) but do not kill spores
o Are relatively non-toxic but have a dehydrating effect on skin (hydrolyze lipids)
o Act mainly by denaturation of bacterial proteins, but can also inhibit the synthesis of metabolites essential for rapid cell division
o No residual killing effect
o Readily inactivated by organic matter
o Most effective in the presence of water (to a point), thus 70% alcohol is more effective than 95%
o Often used to clean the skin prior to venipuncture or immunization
o Not as effective as iodine containing compounds
Phenolic Compounds
Penetrate and disrupt the cell wall in high concentrations and denature proteins and lipids within the cytoplasmic membrane and lyse the cells. Low concentrations of phenol inactivate essential bacterial enzyme systems and cause leakage of essential metabolites from the cell wall.
o Kill most microbes (including Mycobacteria) but do not kill spores
o Rarely used today
o Their antimicrobial action is improved by halogens (e.g. hexachlorophene).
Iodine-Containing Solutions
are the most effective skin antiseptics used in medical practice and SHOULD BE APPLIED BEFORE OBTAINING A BLOOD CULTURE (KNOW THIS) and installing intravenous catheters to remove problematic contaminants like Staphylococcus epidermidis, a member of the skin flora.
o Kill many microorganisms but not spores.
o Often used with alcohols for skin disinfection.
o Are slightly more toxic to skin than alcohols, have some residual antiseptic ability, but are inactivated by organic matter
o Can quickly penetrate the cell wall of microorganisms and cause disruption of proteins and nucleic acid structure and synthesis.
What are the two major types of Iodine-Containing Compounds?
o Two major types of iodine containing compounds are:
Tincture of iodine (2% solution of iodine and potassium iodide in ethanol) is effective at preparing the skin prior to blood culture. However, it can irritate the skin so should be removed with alcohol.
Iodophors are a combination of iodine and a stabilizing agent or carrier. Povidone iodine is the best-known and most commonly used iodophor. It is a stable, non-toxic agent for skin and tissue.
Chlorhexidine
An antiseptic that has broad antimicrobial activity but a slower rate of killing than alcohols.
o Kills microorganisms by membrane disruption but not spores
o Have some residual activity but it is diminished by organic matter and high pH
o Often used for general skin cleansing, a surgical scrub, and a pre-operative skin preparation.
o Some studies have shown chlorhexidine to be a better skin disinfectant in preventing bloodstream infections in patients with central lines as compared to povidone iodine
Quaternary Ammonium Compounds
e.g. Benzalkonium Chloride
o Attack energy-producing enzymes, denature cell proteins and disrupt the cell membranes
o Are not very effective against a number of organisms e.g. Pseudomonas, viruses, spores, mycobacteria etc…
Mnemonic: “to sQuat takes energy”
Triclosan
found in antiseptic hand soaps, some tooth paste products
o Active against bacteria including some mycobacteria but DOES NOT KILL bacterial spores.
o Inhibits bacterial lipid synthesis and may also disrupt the cell membrane at high concentrations.
Mneomnic: “Triclosans TRI to kill spores but cannot”
Pasteurization
It is the process of heating liquids (like milk, beer or fruit juices) to a specific temperature (55-75°C) for a specific period of time in order to destroy harmful organisms like viruses, bacteria, protozoa, molds, and yeast. It does not destroy spores.
• No intended to kill all pathogenic microorganisms in the food
• Aims to achieve a “logarithmic reduction” in the number of viable organisms, reducing their number so they are unlikely to cause disease (assuming the pasteurized product is refrigerated and consumed before its expiration date).
• Commercial-scale sterilization of food is not common, because it adversely affects the taste and quality of the product, thus pasteurization is more commonly used.
