Asepis Sterilization And Disifetion Notes

Asepis Sterilization And Disifetion

Surgical Patient

• In spite of scientific advances in understanding pathogenesis of various diseases and better understanding of pharmacotherapy, infection remains the ‘number one’ enemy for surgeons. So, every attempt should be made to minimise the infection rates in the ward, hospital, and in operation theatre.
• Joseph Lister called infective agents disease dust and introduced carbolic acid spray as an antiseptic agent. Hence, Joseph Lister is called the father of modern surgery.

This chapter deals with fundamental principles of various methods of sterilisation and disinfection and their usage in day-today clinical practice.

1. Sterilisation is defined as a process by which an article, object, or surface is free of all microorganisms in the vegetative form and in the spore state. This includes viruses, bacteria, their spores, and fungi.
2. Disinfection means destruction of all pathogenic organisms capable of giving rise to infection. Rarely does this process kill spores. Disinfection must never be used when sterilisation is possible.
3. Asepsis means being free of sepsis.
4. Antisepsis means prevention of infection by inhibiting the growth of bacteria in wounds or tissues.

Read And Learn More: Basic Principles Of Surgery Notes

Agents Used in Sterilisation

Gives the classification of agents used in sterilisation.

Agents Classification:

Physical agents –  Chemical agents:

• Sunlight  – Alcohol
• Drying  – Aldehyde
• Heat –  Dye
  • Dry heat – Halogens
  • Moist heat  – Phenols and cresols
• Filtration –  Gases
• Radiation  – Surface-active agents

– Metallic salts

Physical Agents

1. Sunlight:

It is an example of a natural bactericidal agent which causes sterilisation of tank water, rivers, etc. It is mainly because of ultraviolet rays in addition to heat rays.

2. Drying:

Drying in air has ill-effects on growth of bacteria. In fact, 80% of weight of bacteria is due to water. However, it does not affect spores and it is an unreliable method.

3.  Heat: Heat is the most commonly employed and most reliable method of sterilisation.

  Heat Two Types:

1. Dry heat
2. Moist heat

Heat:

1. Most reliable
2. Rapid method of sterilisation
3. No harmful residue

1. Dry Heat:

This method of heat kills the organisms by protein denaturation and oxidative damage.

Dry Heat Types

1. Red heat: Inoculating loop or wires, tip of forceps, and needles are held in the flame of a Bunsen burner till they become red hot.
2. Flaming: Glass slides, scalpels, and mouths of culture tubes are passed through Bunsen flame a few times.
3. Incineration: This is used to destroy soiled dressings, bedding, bandages, etc.
4. Hot air oven is the most widely used method of sterilisation by dry heat.

Temperature required is 160°C for one hour or 180°C for 20 minutes.

• Glassware, forceps, scissors, scalpel glass syringe can be sterilized. Materials like oils, greases, dry powder, etc. can also be sterilized by this method.

Hot Air Oven:

1. Glass syringes, test tubes, pipettes
2. Metal forceps, scissors, scalpels
3. Oil, jelly, powder
4. Swab sticks

Sterilisation control—indicators:

1. Spores of nontoxigenic strain of Clostridium tetani
2. Browne’s tube
3. Thermocouples.

2. Moist Heat:

This method of heat kills organisms by coagulation and denaturation of their proteins. In case of spores, steam condenses on it, increases its water content, causes hydrolysis and breakdown of the bacterial protein.

Moist Heat Types:

1. Moist Heat  At temperatures below 100°C:

• Pasteurisation: Temperature of 63°C for 30 minutes (holder method) or 72°C for 15 to 20 seconds (flash method), followed by cooling quickly to 13°C or lower. Mycobacteria, brucellae, and salmonellae are destroyed by this method but spores are not destroyed.
• Inspissation: Serum or egg media (LowensteinJensen media) are sterilized in the inspissator at 80–85°C for half an hour on three consecutive days.
• Vaccine bath: Vaccines of nonsporing bacteria are sterilised in special vaccine baths at 60°C for one hour.

2. Moist Heat  At 100°C:

1.  Boiling (temperature 100°C): Vegetative bacteria are killed at 100°C but sporing bacteria require considerable time for boiling. Hence, boiling is not recommended for sterilising instruments.
2. Tyndallisation: Steam at 100°C for 20 minutes on three consecutive days. It is used for sterilisation of egg, serum, or sugar containing media.
3. Autoclaving or steam under pressure (temperature above 100°C): This is the most popular method.

Principle:

• Water boils when its vapour pressure equals that of surrounding atmosphere. When pressure inside a closed vessel increases, the temperature at which water boils also increases.
• When steam comes into contact with cooler surface, it condenses to water and gives up its latent heat to that surface.
• Condensed water ensures moist conditions for killing the microbes present. All the air must be removed from autoclave chamber before autoclaving.

Temperature employed:

• Sterilisation is carried outbetween 108°C and 147°C. Commonly, temperature of 121°C at 15 lb pressure for 15 minutes is used.
• Thus dressings, instruments, laboratory-ware, media can be sterilised with autoclaving. However, it is not suitable for bottled fluids.

Sterilisation control: Spores of Bacillus stearothumophilus are used as test organisms.

1. Chemical indicators: Browne’s tubes
2. Thermocouples
3. Autoclave tapes.

4. Physical Agents Filtration:

• It is used to get rid of microorganisms from heat-labile liquids and substances such as sugars and urea, which are used for the preparation of media.
• Hence, it is useful for antibiotic solutions, sera, and carbohydrate solutions used in the preparation of culture medium. Different types of filters include earthenware filters, asbestos filters, sintered glass filters, membrane filters, etc.

5. Physical Agents Radiation:

• Nonionising radiation: Low energy type, for example:
  • Infrared radiation: Used for mass sterilization of syringes.
  • Ultraviolet radiation: This can be used to disinfect hospital ward, operation theatres, viral laboratories, etc.
• Ionising radiation: X-rays, and gamma rays are examples. They have high penetration power and are highly lethal to all cells including bacteria.

Gamma radiation is used to sterilize plastic tubes, catheters, syringes, culture plates, etc. This method is also known as cold sterilization, as there is no appreciable increase in the temperature.

Chemical Agents

• Chemical agents act by protein coagulation and disruption of cell membranes. They are mainly used for disinfection rather than sterilisation.
• Disinfectants are antimicrobial agents used to kill potentially infectious agents present on inanimate object, example surfaces, water, etc.
• Chemical disinfectants which can be safely applied to skin or mucous membrane and are used to prevent infection by inhibiting the growth of bacteria are called antiseptics.

1. Chemical agents Alcohols:

• Chemical agentsEthyl alcohol (ethanol) and isopropyl alcohol are commonly used. They rapidly kill bacteria, including tubercle bacilli, but they have no action on spores and viruses.
• They are used in the concentration of 60–70% in water as skin antiseptics before a surgical incision. Isopropyl alcohol is better than ethanol because it is fat solvent, more bactericidal, and less volatile.
• Hence, it is used to disinfect clinical thermometers. Methyl alcohol is effective against fungal spores. However, it is toxic and inflammable and hence, not used.

2. Chemical agents Aldehydes:

They are bactericidal and sporicidal.

Formaldehyde (HCHO): This is used to preserve anatomical specimen. It is an irritant, water-soluble gas.

• Formaldehyde gas is used to fumigate wards, sick rooms, etc.

Glutaraldehyde: It is effective against tubercle bacilli, fungi, and viruses. It is less irritant than formaldehyde.

• This is used to sterilise cystoscopes, bronchoscopes, endotracheal tubes, and metal instruments, which are heat-sensitive.
• 2% buffered solution is used.
• It has no deleterious effect on cement or lenses of instrument.
• Commercially available as ‘Cidex’.

3. Chemical agents Dyes:

• They are aniline dyes and acridines which are used as skin and wound antiseptics. Acriflavine, proflavine are examples for acridine dyes.
• They act against gram-positive and gram-negative organisms. They are little, if at all, affected by presence of pus.
• Whenever a cavity has to be packed or a tie over dressing to be applied following skin grafting, gauze soaked in acriflavine can be used.

Aniline Dyes:

1. Brilliant green, malachite green, crystal violet
2. More active against gram-positive organisms
3. Pus inhibits their activity

4. Chemical agents Halogens:

Iodine is a bactericidal agent with moderate activity on spores. It is also active against tubercle bacillus. Iodine is used almost exclusively as a skin disinfectant (antiseptic).

• Mixtures of iodine with surface-active agents that act as carrier for iodine are known as iodophores. Betadine is an example of this. This is also active against fungi, trichomonas.
• When chlorine or hypochlorites are added to water, the chlorine reacts with water to form hypochlorous acid. It is a strong oxidizing agent and effective disinfectant.
• Chlorine and hypochlorite solution (EUSOL) also are other examples.

5. Chemical agents Phenols and Cresols:

• These are obtained by distillation of coal between temperatures of 170°C and 270°C. They cause cell membrane damage.
• Phenol (carbolic acid) was introduced first by Lister, father of antiseptic surgery. It is a powerful microbicidal substance. It is bactericidal at a concentration of 1%.
• Lysol, cresols, chlorhexidine are also phenols.
• Chlorhexidine (hibitane) is nontoxic, skin antiseptic, active against gram-positive and gram-negative organisms, and moderately active against mycobacteria.

6. Chemical agents Gases (Vapour-Phase Disinfectants)

1. Ethylene oxide: It is a highly inflammable, colourless gas. Hence, it is mixed with inert gases such as carbon dioxide or nitrogen so that its explosive tendency is eliminated. It is highly lethal to all kinds of microbes including spores and tubercle bacilli.
   1. It is used for sterilising heart-lung equipment, books, clothing, glass, plastic, etc. Thus routinely used catheters such as Foley’s catheters, Ryle’s tube, etc. are sterilised by ethylene oxide gas.
2. Formaldehyde gas: Used for fumigation of operation theatres and rooms, often after doing septic case.
3. Betapropiolactone: It is also used for fumigating purposes. It is also active against viruses.

7. Surface-active Agents:

• Substances that alter energy relationships at interfaces leading to reduction of surface or interfacial tension are known as surface-active agents or surfactants. They are used as wetting agents, detergents, etc.
• The most commonly used preparations are cationic surface-active agents. They are bactericidal. They have no action on spores, tubercle bacilli, etc.
• Commercially available preparation include cetrimide (cetavlon). They are most active in alkaline pH. Pseudomonas aeruginosa is particularly resistant to these compounds. Soaps are also active against gram-positive and gramnegative organisms.

8. Metallic Salts:

The salts of silver, copper, and mercury are used as disinfectants. Mercurochrome is less toxic and is used as mild antiseptic.

• Clinically it is used in the treatment of skin grafted ulcers after the graft has taken up well.
• Few examples of sterilization are given in Key.

Quick Revision of Sterilization of Commonly Used Instruments in the Operation Theatre:

1. Surgeon’s knife (scalpel): Glutaraldehyde
2. Forceps, retractors, etc.: Hot air oven
3. Foley’s catheter: Gas sterilisation (ethylene oxide)
4. Glass syringes: Hot air oven
5. Operation theatre: Formaldehyde gas
6. Clinical thermometer: Isopropyl alcohol

Testing Of Disinfectants

1. Rideal-Walker test: Phenol is taken as standard disinfectant. Suspension of typhoid bacilli is subjected to the action of varying concentrations of phenol and the disinfectant to be tested and compared with phenol.
2.  Chick-Martin test: Disinfectant acts in presence of organic matter.