- Sterilization involves killing or removing all forms of microbial life, including endospores, from a material object. It is an absolute process typically achieved through heating.
- Disinfection aims to reduce the number of pathogenic microorganisms (except endospores) to a point where they no longer cause diseases.
- Disinfectants are chemicals used to clean inanimate objects and have an effect on disinfection.
- Antisepsis is the prevention of infection, usually by inhibiting the growth of bacteria, and antiseptics are chemical disinfectants applied safely to the skin or mucous membranes to prevent infection by inhibiting the growth of bacteria or killing them.
- Sanitization involves lowering microbial counts to prevent transmission in a public setting, such as restaurants or public restrooms.
- Degerming refers to the mechanical removal of microbes, such as through handwashing.
- Historical figures like J. Lister and William Stewart Halsted made significant contributions to the field of sterilization and disinfection.
- Objects can be categorized as critical, semi-critical, or non-critical based on their need for sterilization or disinfection.
- There are various categories of disinfectants, including sterilants, high-level disinfectants, intermediate-level disinfectants, and low-level disinfectants.
- Bacterial growth follows an exponential pattern with distinct phases, including the log phase when bacteria are most susceptible to treatments.
- Measurement of microbial death involves the D-value, which is the dose required to inactivate 90% of the initial population of a microorganism.
- Factors affecting sterilization and disinfection include prior cleaning of objects, organic and inorganic load, type and level of microbial contamination, concentration and nature of the germicide used, physical nature of objects, presence of biofilms, temperature, pH, and humidity.
- Different methods of sterilization include physical agents like heat, filtration, and ultrasonic vibrations, as well as chemical agents like alcohol, aldehydes, halogens, surface-active agents, metallic salts, and gases like ethylene oxide and formaldehyde.- Bactericidal activity of ethanol is slightly greater
- Used as an antiseptic to prepare the skin before procedures or injections on broken or intact skin
- After sealing windows and outlets, a mixture of potassium permanganate and formalin is used to generate formaldehyde gas
- No deleterious effects on lenses or instruments like cystoscopes and bronchoscopes
- Chlorine is commonly used as hypochlorite, which is bactericidal and also active against viruses
- High concentrations damage cell membranes, while low concentrations precipitate proteins and affect membrane-bound enzymes
- Limited activity against Gram-negative bacteria and negligible sporicidal activity
- Ethylene Oxide: Alkylating agent used for sterilization of heat-sensitive medical devices
- New disinfectant and sterilization methods include Ortho-phthaladehyde, Antimicrobial coatings, and Superoxide water
- Correct hand wash technique includes using antiseptic solutions like alcohol gel or chlorhexidine gluconate
- Includes sunlight exposure, drying, dry heat methods like flaming and incineration, moist heat methods like pasteurization and steam, filtration methods, and ultrasonic vibrations
STERILIZATION AND DISINFECTION IN OTOLARYNGOLOGY
STERILIZATION
Killing or removing all forms of microbial life (including endospores) in a material or an object
An absolute process.
Heating.
DISINFECTION
Reducing the number of pathogenic microorganisms (except endospores) to the point where they no longer cause diseases.
DISINFECTANT
Chemicals used to clean inanimate objects to effect disinfection.
ANTISEPSIS
Prevention of infection, usually by inhibiting the growth of bacteria.
ANTISEPTICS
Chemical disinfectants applied safely to skin or mucous membrane prevent infection by inhibiting the growth of bacteria or by killing them
SANITISATION
Lowering of microbial counts to prevent transmission in public setting
(e.g., restaurants & public rest rooms)
DEGERMING
Mechanical removal of microbes
e.g., from hands with washing
HISTORICAL BACKGROUND
J. Lister (1827-1892) carbolic acid (phenols)
William Stewart Halsted (1852-1922) : introduction of surgical gloves.
APPROACH TO STERILIZATION & DISINFECTION
CRITICAL OBJECTS
Examples : implants, vascular catheters, needles, arthroscopes, scalpels
SEMI CRITICAL OBJECTS
Examples : endoscopes, endotracheal tubes
NON CRITICAL OBJECTS
Examples: bed sheets ,urinals, stethescope, bed pans
CATEGORIES OF DISINFECTANTS
STERILIANTS
destroy all microorganism
6-10 hours
for critical items
Examples : Glutaraldehyde 2%, Hydrogen peroxide, Ethylene oxide
HIGH LEVEL DISINFECTANT
destroy all viruses and vegetative microorganism
do not reliably kill endospores.
used for time period as short as 30 min .
used to treat semi critical items
Examples: Glutaraldehyde, Peracetic acid
INTERMEDIATE LEVEL DISINFECTANTS
destroy all vegetative bacteria, fungi and most viruses
do not kill endospores even with prolonged exposure
used to disinfectant non- critical instrument
Examples : Chlorines, Ammonium compounds
LOW LEVEL DISINFECTANTS
destroy fungi, vegetative bacteria except mycobacterium and enveloped viruses
do not kill endospores nor destroy naked viruses
general-purpose disinfectants
Examples : Quarternary ammonium compounds, Phenolics
BACTERIAL GROWTH
Expontial growth pattern
4 phases
Most succeptible in the log phase
Different Kinds of Bacteria “Death”
Bactericidal
Bacteriostatic
Bacteriolytic
Exponential Death
Measurement of Microbial Death
No. of viable cells decreases exponentially with extent of exposure
D-Value (decimal reduction value) dose required to inactivate 90% of initial population.
Species or strain of micro-organisms
FACTORS AFFECTING STERILISATION & DISINFECTION
Prior cleaning of objects
Organic and inorganic load
Type and level of microbial contamination
Concentration and nature of germicide
Physical nature of objects
Presence of biofilms
Temperature, PH and Humidity
PROCESS
CLEANSING
Removal of soil or organic material from instruments and equipment clinically
Rinsing the object under cold water
Applying detergent and scrubbing object
Rinsing the object under warm water
Drying the object prior to sterilization
Methods of Sterilisation
METHODS OF STERILISATION
PHYSICAL METHOD
Sunlight
Drying
Dry heat: Flaming, Hot air, Incineration
Moist heat : Pasteurization, Boiling, Steam
Filtration: Candles, Asbestos pads, Membrane
Ultrasonic and sonic vibrations
CHEMICAL METHODS
Alcohol: Ethyl ,Isopropyl
Aldehydes: Formaldehydes, Glutaraldehyde , Orthophthaldehyde
Halogens
Phenol
Surface-active agents
Metallic salts
Gases : Ethylene oxide, Formaldehyde,Betapropriolactone
PHYSICAL METHODS
SUNLIGHT:
Appreciable bactericidal activity under natural conditions
ultraviolet ray
Sterilizing power varies according to circumstances
In tropical countryside
Example: typhoid bacilli exposed to sunlight killed within 2 hours
HEAT
Most reliable method
Whenever possible , should be the method of choice
Dry/moist/pasteurization
Factors responsible
Nature of heat : Dry/Moist
Temperature and Time
Number of organism present
Characteristic of organism : Species, Strain, Sporing capacity
Nature of material
Mechanism of action
Protein denaturation
Oxidative damage
Coagulation of protein
Protein damage
DRY HEAT
(A) Flaming
Uses: Scalpels, needles
(B) Incineration
Soiled dressing, pathological material
Plastic such as PVC and polythene (but polystyrene material emits clouds of dense smoke and hence should not be incinerated)
(c) Hot Air Oven
Dry heat
Hot air (bad conductor of heat with low penetrating power)
Oven heated by electricity with heating electrode in wall of chamber
Fan within the chamber
Materials evenly placed for free circulation of air in between objects
Uses:
Forceps, Scissor, Scalpel, Glassware, Liquid paraffin, Dusting powder, Glycerol
Standing time
Cutting instrument: 150° c for 2 hour
Others: 160° C for 1 hour
MOIST HEAT
Latent heat liberated when condensed on a cooler surface
Increased water content on spores : hydrolysis and breakdown of bacterial protein
In a moisture free atmosphere, bacteria like protein more resistant to heat
Moist heat preferred to dry heat for killing
PASTEURISATION
- Devised by L.Pasteur as a means of destroying microorganism that cause spoilage of wine and beer
Milk:
Holder method : 63° C for 30 min
Flash method: 72° C for 15 followed by rapid cooling to 13° C or lower
Doesn’t sterilize the milk
Does kill all disease producing bacteria commonly transmitted by milk
Water Bath
Most non sporing bacteria : 60° C for 30 min
Staphylococcus aureus and Streptococcus fecalis: 60° C for 60 min
Vegetative form of bacteria, yeast and moulds: 80°C for 5-10 mins
Spore of Clostridium botulism (most heat resistant):120° C for 4 hours, 100° C for 330 min
Viruses: Polio virus: 60° C for 30 min
Boiling
Not recommended for sterilization .
Only as means of disinfecting of surgical instrument.
Vegetative bacteria killed at 90 -100°C.
Spore require considerable period of boiling.
Holding time : 10 – 30 min.
AUTOCLAVE AND STEAM STERILIZER
Principle:
Usually exposure for 20 min at 121 °C, at a steam pressure of 15 pound for square inch (psi)
Mininum recommended time for heat sterlization
Types of Steam Sterilizer
For porous loads- dressings, textiles, wrapped instruments and utensils – trap air.
For fluids in sealed containers-
pharmaceutical fluids, lab. media, ampoules – not to open door until 800C- may explode.
For unwrapped instruments and utensils.
Laboratory Sterilizers.
DESIGN OF AUTOCLAVE
Vertical or horizontal cylinder.
Made up of gunmetal/stainless steel.
Sheet – iron case
Lid or door fastened by screw and made tight by asbestos washer.
Heating done by gas or electricity.
INSTACLAVE VACUM
Sterilizer with active air removal system
Can be used for sterilizing instruments enclosed in any form of wrapping, hollow items or devices with lumens and porous materials.
Vacuum Sterilization Process
Application of vapour of a mixture of peracetic acid with hydrogen peroxide and residual gas from atmospheric air
Excited by pulsed electrical discharge
Process of sterilization in vacuum, dry, and at low temperature (room temperature )
FILTRATION
Used for heat liable liquid to make them microorganism free
e.g. antibiotic solution,
Clinically not used
Types: candles filters, asbestos filter, membrane filter
Commonly used for water purifying
High Efficiency Particulate Air Filter(HEPA)
Special filters which removes nearly all microorganism from air that have a diameter greater than 0.34 µm.
Used in operation theatres and labs where potentially dangerous airborne pathogens such as mycobacterium are handled.
RADIATION
Electromagnetic waves having energy but no mass.
Shorter the wavelength (gamma rays), higher the killing power.
Non ionizing : infra red and UV rays.
Ionizing : gamma rays.
Damage DNA by producing reactive molecule such as super oxide and hydroxyl free radical.
NONIONIZING RADIATION
Electromagnetic rays with wavelength longer than that of visible light
Some are absorbed as heat
e .g.-Infrared : Rapid sterilization of syringe
Ultraviolet: Disinfecting enclosed area : hospital wards, OT, virus lab
IONIZING RADIATION
Highly lethal to DNA and other cell constituents
High penetrating power
No increase in temperature: Cold sterilization
e.g., X ray, Gamma rays, Cosmic rays
Gamma rays: Plastic syringe, Catheters, Metal foils
CHEMICAL METHODS
Different chemical agents used
An ideal agent
Wide spectrum
Speedy action
Active in presence of organic matter, acid, alkali
Stable and high penetrating power
Non irritant, non toxic, non interfering with healing
Cheap, safe, and easy to use
EVALUATION OF DISINFECTANT
Phenol coefficient
Compares efficacy to that of phenol
With greater efficacy indicated with coefficient >1
Salmonella typhi and Staphylococcus aureus commonly used to determine coefficients
Disc diffusion method
Placement of disinfectant impregnated filter paper on well-inoculated agar
MECHANISM OF ACTION
Protein coagulation
Disruption of cell membrane
Damage to nucleic acid
Substrate competition
ALCOHOL
Mechanism
Denaturation of protein
Change in cell membrane
Agents
Ethyl alcohol (Ethanol)
Isopropyl alcohol
- Not reliable agents for sterilization
- Unable to kill spores at normal temperature
- Evaporate quickly which limit effective contact time and effectiveness
ETHANOL
Used mainly as skin antiseptics
Bactericidal action
Remove lipid from skin
Conc. of 60-70 % in water effective
ISOPROPYL ALCOHOL
Bactericidal activity slightly greater than that of ethanol
Less volatile
Recommended as a replacement for ethanol
Toxic effect greater and longer than produced by ethanol like necrosis
USES
As antiseptic to prepare skin for procedure such as injection that breaks the intact skin
As disinfectants for treating instrument
May damage some material like rubber
ALDEHYDES
Mechanism
Alkylating agents acts on protein
cause enzyme modification and inhibition
FORMALDEHYDE
In aqueous sol:
Markedly bactericidal , sporicidal and Virucidal effect
Uses
10 % formaldehyde
- To clean metal instrument
- Preserve anatomical bodies
Formalin:
- An aqueous sol of 37 % formaldehyde
- 0.2% to 0.4% formalin
- Used to inactivate viruses for vaccine preparation
OT FUMIGATION:
After sealing windows and other outlet
150 gm of Kmno4 and 280ml of formalin is mixed to generate formaldehyde gas
After generating vapour, door is sealed for 48 hours
GLUTARALDEHYDE
Action similar to formaldehyde
Specially effective against tubercle bacilli, fungi and virus
10 times more potent than formaldehyde
Less toxic and irritant to eyes and skin
No deleterious effect on lenses of instrument such as cystoscope and bronchoscope
Uses
2 % glutaraldehyde as cold sterilant for surgical instrument
-Endoscopes
-Endotracheal tube
-Metal instrument
-Polythene tubing
Immersion for 10 -12 hours: destroy all form of microbial life including endospores and virus
10 min: destroy vegetative bacteria
Toxic,thorough rinsing of treated items before us
HYDROGEN PEROXIDE
Oxidizing Agent
3 % sol harmless but weak antiseptic
Use: Cleaning of wound
Mechanism
Toxic free hydroxyl radical which damage DNA
Uses
Disinfection of surgical devices , soft plastic contact lens
Halogens
Chlorine and its compound
Used as disinfectant for many years
Chlorine is most commonly used as hypochlorite
Bactericidal and also active against viruses
In water supplies swimming pool, food and dairy industry
Too irritating to skin and mucous membrane to be used as antiseptic
e.g.,: 5% sodium hypochlorite used to disinfect instrument
Chlorites/ Hypochlorites
Broad-spectrum, inexpensive
Disinfectants of choice – viruses and HBV
Heavy soilage (blood spillage) – conc. 10000 ppm – recommended
Inactivated by organic matter, corrode metals, bleaching action
Iodine
Inactivated by organic matter
Staining and hypersensitivity
Iodophors – iodine + anionic detergent
Povidine iodine – iodine + polyvinyl pyrrolidone
Tincture – iodine + alcohol
Less irritant and staining
Skin disinfection and pre-operative preparation of skin
Tincture: Iodine dissolved in alcohol
IODOPHORES
Iodine is linked to carrier molecule that
release free (unbound) iodine slowly
Carriers increase the solubility of iodine and provide sustained release.
Iodophores are not as irritating to skin as tincture iodine nor are they as likely to stain
Example:Betadine
Compound of 1-vinyl-2-pyrrolidine polymer with iodine not less than 9% and not more than 12% available
Phenols
First used by Lister in 1865
Prepared by distillation of coal tar between 170 and 270 °C
Highly corrosive and toxic
MOA
High conc.: Damage of cell membrane
Low conc.: precipitate protein and membrane bound oxidase and dehydrogenase
Types
1. Lysol and cresol
2. Chlorophenol and chloroxyphenols
Lysol and Cresol:
Not readily inactivated by presence of organic matter
Good disinfectant
Chlorophenol and Chloroxyphenols:
Less toxic
Less active and more readily inactivated by organic matter
Uses: Disinfecting ward
Mixed with soaps/ various cosmetic preparation
Biguanides
Chlorhexidine
Commonly used – skin and mucous membrane
Less active – Gm –ve bacteria like Psudomonas and Proteus, limited virucidal, tuberculocidal and negligible sporicidal
Combined with detergent/alcohol – handwashing/ hand rub
Low irritant and low toxic
Inactivated by organic matter, soap, anionic detergents, hard water and cork liners of bottle closures
Gaseous Processes
Ethylene Oxide:
Alkylating agent
Highly penetrative, non-corrosive
microbicidal gas
Temperature<600C with high relative humidity
Gas conc. – 7000-1000 mg/l at 45-600C and relative humidity above 70% for 2 hrs
MOA- reacts with protein, DNA and RNA
Uses: used in industry for single-use items, heat sensitive medical devices like tracheostomy tube, prosthetic heart valves, plastic catheters
NEW DISINFECTANT AND STERILIZATION METHODS
Disinfection:
Ortho-phthaladehyde (OPA)
Antimicrobial coating (surfacine)
Superoxide water (sterilox)
Sterilization
Liquid sterilization process (endocleans)
New plasma sterilizer (sterrad 50)
E Beam sterilisation
OPA: ORTHO-PHTHALADEHYDE
Clear pale blue liquid
Conc.: 0.55%
Superior to glutaraldehyde
Advantages over glutaraldehyde
Requires no activation
Non irritant to eyes and nasal passage
Stability over wide range of pH (3-9)
Barely perceptible odour
Standing time (12 hours Vs 12 min)
Disadvantages
Stains protein gray (including unprotected skin), thus be handled with caution
High cost
Immersion time: At 200C 12 min by FDA (varies from 5 to 12 min)
SUPEROXIDE WATER
Concept is electrolyzing saline to create disinfectant
Saline passed over titanium –coated electrodes
Main products are hypochlorous acid and free chlorine radicals
Product generated has PH of 5 to 6.5
Disinfectant is generated at point of use
Contact time :<2 min
Advantages
Basic material (saline and electricity) are inexpensive
Non toxic to biological tissue
Disadvantages
Production equipment are expensive
Limited use life (must be freshly generated)
ENDOCLEANS
Computer controlled endoscope – reprocessing machine
A system designed to provide rapid, automated, point of use sterilization
It contains performic acid (hydrogen peroxide and formic acid)
Advantages
Device automatically cleans and sterilizes
Rapid cycle time ( < 30 min)
Disadvantages
Use of immersible instrument only
Point of use system, no longer storage
HYDROGEN PEROXIDE PLASMA
Low temperature sterilization technology
For temp sensitive equipment
Process involves: Sterilization in a chamber using H2O2 vapour diffusion
As effective as ethylene oxide
Contact time : 45 min to 72 min
Advantages
Reduced cycle time: 45 min
Disadvantages
Costly
Endoscope with length > 40 cm can’t be processed
Surgical instrument (METALLIC) : Autoclave
Plastic, rubber (suction tube, cautery): Formaldehyde gas
Gel foam: Ethylene gas, Hot air oven
Grommet, Teflon piston: Autoclave
Lacrimal (DCR stent) ET tube, Syringe, Drain (romovac), NG tube: Gas, Ethylene oxide
Surgical blade: Gamma radiation
Suture material: 90% isopropyl alcohol
IV cannula, syringe: Gamma radiation
OPD (examination) instrument: Boiling
OT: Ethylene oxide, autoclave, formaldehyde gas, OPA, alcohol and povidine iodine
WARD: Chlorine, alcohol, glutaraldehyde and povidine iodine
OPD: Alcohol, Boiling, glutaradehyde and povidine iodine.
STERILISATION OF HIV CONTAMINATD OBJECTS AND SURFACES
Always sterilise instruments after each use
Place instruments in a 0.5% chlorine solution after use to prevent fluids from becoming dry and difficult to remove
Wash well with a brush and soapy water
Methods
Steam under pressure for at least 20 minutes.
Heat in an electric oven for 2 hours at 170°C (340°F).
Boil in water for 20 minutes
Soak in one of the chemicals listed for 30 minutes. ( not suitable for sterilising needles and syringes.)
Polyvidone iodine 2%
Chloride solution 0.5%
Glutaraldehde 2%
Rubbing alcohol 70%
Surgical spirit 70%
Hydrogen peroxide 6%
(Disinfectants such as Lysol, Savlon and Dettol will not kill the HIV virus )
Disinfected surfaces and bedding
Wipe surfaces with one of the chemicals which kill HIV if there are spills of blood and fluid
Cover blood and vomit spillages with one of these chemicals
Leave for a few minutes first and then clean up, wearing gloves
Burn cleaning materials or disinfect them
UNIVERSAL PRECAUTIONS
Consider every person potentially infectious
Wash hands
Wear gloves
Use physical barriers
Use antiseptic agents
Use safe work practice
Safely dispose infectious wastes
Process used items
Key components
Hand washing
Gloves
Masks and Goggles
Gowns
Linen
Patient care equipments
Environmental cleaning
Sharps
HAND HYGIENE
Hand washing one of the most important procedures for preventing the spread of disease principle route by which cross infection occurs.
Choice of cleansing agent
Antiseptic Solutions
Alcohol Gel
Chlorhexidine Gluconate
Povidone Iodine
Correct hand wash technique
A six-step hand washing technique has been devised by
-Ayliffe et al ,1992
Wet hands under running water
Dispense one dose of soap into cupped hands
Hand wash for 10-15 seconds vigorously and thoroughly, without adding more water
Rinse hands thoroughly under running water
Dry hands with disposable paper towel
Six-step hand wash technique
Rub palm to palm
Right palm over left dorsum and left palm over right dorsum
Palm to palm fingers interlaced
Back of fingers to opposing palms with fingers interlaced
Rotational rubbing of right thumb clasped in left palm and vice versa
Rotational rubbing back and forwards with clasped fingers of right hand in left palm and vice versa
METHODS OF STERILISATION
PHYSICAL METHOD
Sunlight
Drying
Dry heat: Flaming, Hot air, Incineration
Moist heat : Pasteurization, Boiling, Steam
Filtration: Candles, Asbestos pads, Membrane
Ultrasonic and sonic vibrations
