Sterilization, Disinfection, and Asepsis

Sterilization

• Sterilization is a process that frees an article, surface, or medium from all living microorganisms, including both vegetative and spore states.
• The goal is to eliminate or kill microorganisms.

Disinfection

• Disinfection kills or removes most vegetative microorganisms, but not spores, from non-living objects.

Asepsis

• Asepsis prevents microbial contamination of a person, object, wound, or tissue.

Antiseptics

• Antiseptics are chemical agents safe for use on living tissues.
• They prevent infection by inhibiting bacterial growth.

Bactericidal vs. Bacteriostatic

• Bactericidal agents kill bacteria; they are also known as germicides, fungicides, and virucides.
• Bacteriostatic agents prevent or stop bacterial growth, and can also be fungistatic or virustatic.

Contamination

• Contamination is the presence of living microbes on an object.

Decontamination

• Decontamination frees an article or area from microorganism contamination.

Microorganisms: Decay, Infection and Contamination

• Microorganisms can cause decay and infections, leading to contamination.

History

• In 1862, Louis Pasteur developed the pasteurization process.
• In 1867, Joseph Lister used carbolic solution spray on patients' wounds.
• In 1876, Charles Chamberland developed the first pressure steam sterilizer (autoclave).

Order of resistance of pathogens

• Prions are the hardest to kill, followed by spores, cysts of parasites, mycobacteria, non-enveloped viruses, fungi, Gram+ bacteria, Gram- bacteria, and, finally, enveloped viruses, which are the easiest to kill.

Methods of Sterilization and Disinfection

• Physical methods include sunlight, drying, dry heat, moist heat, filtration, radiation, and ultrasonic/sonic vibrations.
• Chemical methods include alcohols, aldehydes, dyes, halogens, phenols, surface-active agents, metallic salts, and gases like ethylene oxide, formaldehyde, and beta-propiolactone.

Factors influencing choice of sterilisation/disinfection method

• The choice of method depends on the device's intended use, the risk of infection, and the degree of soiling.
• The process must not damage the device.

Physical Methods of Sterilization

• Common physical methods are heat (dry and moist), radiation, UV light, ionizing radiation, and filtration.

Dry Heat Sterilization

• Dry heat is a reliable sterilization method through mechanisms of protein denaturation, oxidative damage, and electrolyte toxicity from elevated levels.
• Flaming involves using a Bunsen flame until the item is red hot.
• It is used for sterilizing inoculation of wire and loop.
• Incineration, using very high temperatures (600-1000°C), is used for surgical waste, organs, and tissues.

Dry Heat Sterilization - Hot Air

• Hot air sterilization requires hot-air ovens and can be used for glassware, metallic items, and powders.
• Temperatures and times include two hours at 160°C, one hour at 170°C, or 30 minutes at 180°C.
• Plastics, rubber, paper and cloth cannot be sterilized this way due to fire risk.
• It can be used for powders and anhydrous oils and is inexpensive with no corrosive effect.
• A disadvantage is that high temperatures can damage some items and heat penetration is slow and uneven.

Moist Heat Sterilization

• Moist heat uses hot water and kills microorganisms through protein denaturation and coagulation, exhibiting a more effective penetration power than dry heat.
• Temperatures used are typically below 100°C.
• Pasteurization inactivates harmful organisms in milk but does not achieve sterilization, killing only vegetative bacteria, not spores.
• Coxiella burnetiid may survive pasteurization.
  • Holder method is 63°C for 30 minutes.
  • Flash method is 71.7°C for 15-20 seconds.

Moist Heat at 100°C

• Boiling at 100°C kills most vegetative bacteria in minutes, but spores need prolonged time.
• Tyndallisation reduces activity of sporulating bacteria through a simple boiling water method; it involves first killing vegetative bacteria and then providing favorable comedication, followed by another boil.
• Temperature above 100°C uses steam under pressure and effective method for sterilization.
• Water bath: A water bath is conducted at 56°C for 1 hour for serum and vaccine bath is conducted at 60°C for 1 hour for vaccine preparation.

Moist Heat - Autoclaving

• Autoclaving is a standard sterilization method in hospitals working under the same principle as a pressure cooker, where increased pressure raises the boiling point of water to above 100°C.
• The autoclave replaces air with saturated steam in a double-walled chamber.
• The air in the chamber is evacuated and filled with saturated steam and the chamber is closed tightly so steam fills it and the pressure gradually increases.
• Autoclaving can be used to sterilize any material not damaged by steam, like all solid and liquid media, distilled water, saline solution, lab coats, swabs, syringes, needles, surgical instruments and dressing material.

Moist Heat - Autoclaving conditions

• The usual temperature achieved is 121°C at 15 pascals (Pa) of pressure for 15-20 minutes.
• Sterilization time can be reduced by increasing the temperature.

Monitoring Autoclaves

• Physical use of thermocouple to measure accurately the temperature.
• Chemical monitoring uses heat-sensitive chemicals that change color at the correct temperature and exposure time.
  • Examples include autoclave tape and Browne's tubes (green spot).
• Biological monitoring involves adding a spore of Bacillus stearothermophilus during sterilization and culturing later to ensure it has been killed.

Radiation

• Non-ionizing radiation like infrared and UV light has limited sterilizing power because of poor penetration and is non-sporicidal.
• It will irradiate air in certain areas such as operating rooms and TB laboratories.
• Ionizing radiation involves radiation (cold sterilization) using X-rays, cosmic rays, and gamma radiation.
• A Cobalt60 source has greater energy than UV light and is sporicidal, therefore more effective.
• It is mainly used in industrial facilities to sterilize cannulas, cardiac implants, pacemakers, disposable plastic syringes, gloves, specimen containers, and Petri dishes.

Filtration

• Filtration removes bacteria from heat-labile liquids like sera, sugar solutions, or antibiotics.
• This can be done done under negative or positive pressure.
• Membrane filters made from cellulose acetate are best.
• Though; viruses and some small bacteria may pass through, it main use is for heat labile substances for example sera, antibiotics.
• The recommended filter size to exclude the smallest bacterial cells is 0.22 micron.

Ideal Properties of Antiseptics and Disinfectants

• Wide spectrum activity.
• Effective in both acid and alkaline environments.
• Speedy action.
• High penetration power.
• Stable.
• Non-corrosive to metals.
• Does not cause local irritation.
• Non-toxic.
• Inexpensive, easily available, safe, and easy to use.

Activity of Disinfectants

• Activity depends on the level of contamination, concentration of disinfectant, temperature, time, and range of action.

Alcohols

• Ethyl (ethanol) and isopropyl alcohol are used most frequently.
• They are mainly used as skin antiseptics and act by denaturing bacterial proteins.
• The effective concentration is 60-90%, but mostly 70% is used.
• Isopropyl alcohol is used for the disinfection of clinical thermometers.
• Methyl alcohol is effective for fungal control and used for treating cabinets and incubators though the methyl alcohol vapor is toxic and inflammable.

Aldehydes

• Are combined with nucleic acid and protein and inactive them.
• They area also lethal(sporicidal) for viruses.
• Formaldehyde and Glutaraldehyde are used to preserve anatomical specimen.
• The destroy anthrax spores in hair and wool.
• Formaldehyde gas is used for sterilizing instruments and heat-sensitive catheters, and for fumigating wards and laboratories. Additionally, it is an irritant and toxic when inhaled.

Dyes

• The dyes like aniline and acridine are used as skin and wound antiseptics.
  • Aniline dyes that are brilliant green, malachite green and crystal violate are more active against gram positive bacteria, and they are non-toxic and non-irritant.
  • Acridine dyes are more active against gram-negative bacteria.

Halogens

• Iodine and chlorine are halogens.
• Iodine solutions are widely used as skin disinfectants, it is bactericidal which is also active against spores, Mtb and virus.
• Chlorine is used for disinfecting water supplies, swimming pools, and in the food industry.
• Phenol(Lysol and cresol), Hydrogen peroxide, Potassium permanganate

Gases

• Used for sterilization and disinfection include ethylene oxide, formaldehyde gas, betapropiolactone (BPL), and hydrogen peroxide fogging.
• Ethylene oxide is highly penetrating and inflammable and explosive at normal temperature and pressure; mixing it with inert gases such as CO2 or nitrogen to a concentration of 10% eliminates its explosive tendency.
• It is especially used for sterilizing heart-lung machines and respirators.

Effectiveness of Antiseptics and Disinfectants

• Classified by their activity level, reflecting the types of microbes and viruses they are effective against.
  • High-level germicides kill vegetative cells, fungi, viruses, and endospores, leading to sterilization with extended use.
  • Intermediate-level germicides are less effective against endospores and certain viruses.
  • Low-level germicides kill only vegetative cells and certain enveloped viruses, but are ineffective against endospores.

Testing the Effectiveness of Antiseptics and Disinfectants

• In the Rideal-Walker test, the effectiveness of a chemical disinfectant is compared to that of phenol in killing Staphylococcus aureus and Salmonella Typhi, with calculation of a phenol coefficient.
• The disk-diffusion method tests a chemical disinfectant's effectiveness against a particular microbe.
• The use-dilution test determines a disinfectant's effectiveness on a surface.
• In-use or Kelsey-Sykes tests can determine whether disinfectant solutions are correctly used in clinical settings.

Spaulding Classification

• Spaulding's classification system is used to classify devices, it determines the type of method selected for sterilization and disinfection and critical, semi-critical and non-critical items.

Managing Contaminated Reusable Items

• Contaminated reusable items should be handled as little as possible.
• Staff is to wear personal protective equipment ( PPE ).
• Gross debris must be removed at the point of use and soiled items removed immediately after use.

Cleaning Instruments

• Soak the items in enzymatic or nonenzymatic detergent and wear the appropriate PPE.
• Instruments are to be kept submerged in solution and scrub with brush before being thoroughly rinsed and allowed to dry.

Fumigation

• Fumigation is for rooms contaminated with pathogens such as MRSA and Clostridium difficile.
• It is done by releasing hydrogen peroxide, chlorine dioxide gas, or possibly ozone in sealed rooms and it requires special equipment.
• There is a risk of damage to sensitive items.

Plasma Sterilization

• Plasma sterilization is the new methods for heat sensitive articles.
• It is a fourth state of matter and consists of ions, electrons or neutral particles where radio frequency energy is applied to create an electromagnetic field.
• Highly reactive/charged particles from hydrogen peroxide are generated under vacuum.
• It can be used to sterilize heat- and moisture-sensitive items like some plastics, electrical/ electronic devices, and corrosion susceptible metal alloys.
• Special wrapping is required.