STERILIZATION AND

DISINFECTION
Dr. Sharmin Mulla
Sterilization
• Sterilization- It is a process by which all living microorganisms
including viable spores , are either destroyed or removed from an
article, surface or medium.
• Agents – sterilants
• Reduction of ≥10^6log colony forming units of microorganism and
their spores.
Disinfection
• A process that destroys or removes most if not all pathogenic
organisms but may or may not destroy bacterial spores.
• Reduction of ≥10^3 log CFU of most microorganism but not spores.
• Agents- Disinfectants
• Used only on inanimate objects,not on body surfaces
• Classified upon their efficacy- high ,intermediate, low
Antiseptics
• Type of disinfectants which are safe to apply on body surfaces (skin
and mucosa) resulting in the destruction of organisms present on the
body surfaces. This type of disinfection is termed Asepsis.
Cleaning (Decontamination)
• Refers to the reduction in the pathogenic microbial population to a
level at which items are considered as safe without protective attire
• Achieved by manual or mechanical cleaning by soap and detergents
to eliminate debris or organic matter from the medical devices or
surfaces.
• Reduction of at least ≥1 log CFU of most of the microorganism but not
spores.
Agents used in hospital for achieving
sterilization ,disinfection and cleaning.
Agents Physical methods Chemical methods
STERILANTS

Agents of sterilization Steam sterilizer (Autoclave) Ethylene oxide (ETO) sterilizer

Dry heat sterilizer (hot air oven ) Plasma sterilizer
Filtration
Radiation: ionizing and nonionizing
(infrared)
DISINFECTANTS
HIGH LEVEL No physical method Aldehydes , peracetic acid
,hydrogen peroxide

INTERMEDIATE LEVEL Heat based method :boiling Alcohols , phenolics, halogens

UV (nonionizing )radiation

LOW LEVEL No Quaternary ammonium compound

Chlorhexidine
 Central sterile supply department
• Place in hospital that performs sterilization of medical devices,
equipment's, consumables.
• Consists of 4 unidirectional zones starting from an unsterile area to a
sterile area separated by a physical barrier .
• Decontamination area Packaging area Sterilization area
sterile storage area
• Decontamination area- Items are collected and decontaminated /cleaned
by automated machines ,manual wash
• Packaging area items are enclosed in container designed to allow the
penetration and removal of the sterilant during sterilization and then to
protect the device from contamination and other damage following
sterilization and until the time of use.
• Sterilization area- packed medical devices are subjected to
sterilization process by steam sterilizer , ethylene oxide sterilizer or
plasma sterilizer.
• Sterile storage area – after sterilization the sterilized items are stored
in this area . It has an issue counter to supply the items to OTs and
various other areas of the hospital.
STERILANTS
AUTOCLAVE (STEAM STERILIZER)- moist heat of >100◦C.
121◦c for 15 min at a pressure of 15 pounds per square inch.
• pressure chamber :
-consists of a large cylinder –made up of gunmetal or stainless steel, in
which the materials to be sterilized are placed.
-steam jacket (water compartment).
• Lid: discharge tap-passage of air and steam
pressure gauge
safety valve –remove extra steam
• Electrical heater-it is attached to jacket, that heats the water to produce
steam.
types
• Horizontal types
{large volume capacity}
Vertical type {small volume capacity}
uses
• Most commonly used method in the hospital
• surgical instruments ,anesthetic equipment , dental instrument
,implanted medical devices and surgical drapes and linens.
• Culture media preparation
• Biomedical waste treatment
Sterilization control : effectiveness of sterilization can be monitored by
spores of Geobacillus steatothermophillus
ETHYLENE OXIDE STERILIZER
• Widely used gaseous chemical sterilant
• Uses – sterilize critical and semi critical items that are moisture or
heat sensitive and cannot be sterilized by steam sterilization .
• E.g. Heart lung machine components, sutures , catheters, stents,
• Respirators ,dental equipment, devices with electronic components,
multi lumen tubing's.

• Sterilization control- Bacillus atrophaceus

Advantages
Disadvantages
• Large chamber capacity • Highly inflammable,irritant,
• Suitable for heat sensitive items • explosive
• High penetration power • Carcinogenic
• Non corrosive • Long duration cycles
• High cost
Plasma sterilization
• Special device used to create the plasma state
• Uses hydrogen peroxide as chemical sterilant
• Cycle run for 24-75 min (37- 44◦c )
Sterilization control- Bacillus steatothermophillus
Uses- used by CSSD for sterilization of materials and devices that
cannot tolerate high temp, and humidity, such as plastics ,electrical
devices, and corrosion –susceptible metals such as arthroscope ,micro
and vascular instrument, spine sets and laparoscope.
DRY HEAT STERILIZER ( HOT AIR
OVEN )
• Used for material that might be damaged by moist heat or that are
impenetrable to the moist heat .
• Eg . Glass wares ,powders , petroleum products , sharp instruments
• 160◦c for 120 min
• Sterilization control- Bacillus atrophaeus
 FILTRATION
• Acts by removing microorganism , not by killing.
• MEMBRANE FILTERS- most widely used
• FILTRATION OF AIR- 1)HEPA Filters(High efficiency particulate air
filtrates)- biosafety cabinets, airflow system, operation theatre,
isolation rooms. 2)surgical mask , N95 respirators.
• FILTRATION OF LIQUID- 1) bacteriological examination of water in
hospital settings, dialysis water. 2)it is used in to remove bacteria
from heat labile liquids such as remove bacteria from sera, sugar
toxin , vaccine , antibiotic solution.
• Sterilization control- Brevudimonas diminuta, Serratia marcescens
RADIATION
• IONIZING RADIATION/COLD STERILIZATION –low temperature
sterilization , e.g. cobalt 60 gamma rays
• Uses –tissue for transplantation, pharmaceuticals, medical devices.
• Non ionizing radiation- infrared radiation, UV radiation,
DISINFECTANTS
• HIGH LEVEL DISINFECTANT - peracetic acid , H2O2,
Aldehydes- formaldehyde, glutaraldehyde , orthophthaldehyde .
GLUTARALDEHYDE- 2% or 2.4% concentration. It disinfects objects
within 20 min but may require longer time to kill spores(10-14 hrs)
It is in inactive form, has to be activated by alkalinization before use.
Once activated , it remains active only for 14 days.
Uses-endoscopes, cystoscopes, fogging and cleaning of floor ,
operation theatres
H2O2
• Hydroxyl free radical
• Sporicidal at >4-5 %
• 3% -environmental surface disinfection, fogging , wound cleaning
• 3-6%-soft contact lens, tonometer biprisms ventilators,
fabrics,endoscopes.
• 6-7.5% -chemical sterilant in plasma sterilization
 Intermediate level
• ALCOHOL – e.g. ethyl alcohol, isopropyl alcohol. (60-80%)
USES- alcohol based hand rub e.g. Sterillum
-thermometers- immersed in alcohol for 10-15min
- rubber stops of multiple dose medication vials or vaccine bottles and hubs
of the central line ,
-stethoscopes , ventilators, manual ventilation bags, ultrasound machines.
- laboratory bench , medication preparation areas.
-spirits (70%) used as skin antiseptics.
Phenolics

• Phenol- antiseptic and disinfectant

• Disinfectants- cresol, Lysol
• Antiseptics- chloroxylenol(Dettol)
Halogen
Iodine-tincture iodine- antiseptic
povidone iodine-e.g, betadine
Chlorine- sodium hypochlorite-household bleach
calcium hypochlorite-bleaching powder
uses
• Free chlorine- disinfection of municipal water supplies and swimming
pool water, etc
• Sodium hypochlorite- 10-20 min contact time.
Large blood spills- 0.5% (1:10 dilution)
Small blood spills – 0.05% (1:100 )
pretreatment of liquid waste before disposal -1%(1:5)
Laundry items – 0.1% (1:50)
Surface disinfection- 0.5% (1:10)
Low Level disinfectants
• Does not destroy tubercle bacilli and spores
Quaternary ammonium compounds- e.g. – benzyl ammonium chloride
sanitation of floors, furniture, walls , blood pressure cuffs etc.
Chlorhexidine Gluconate- antiseptic (Savlon – chlorhexidine
,cetrimide,isopropyl alcohol)
Hand hygiene- hand rub (0.5%), hand wash (4%) , Mouthwash (0.1-
0.2%), bodywash solutions, skin disinfectant,
Cleaning agents
• Cleaning is performed before the disinfectants are applied.
• Most disinfectants act well only when the instrument or the surface is
free from organic matter, such as dirt , blood etc.
• Cleaning agents
1) Enzymatic cleaners- amylase lipase ,cellulase, protease . they
remove protein from surfaces
2) Cleaning chemicals { detergents}- these agents act by reducing
surface tension and dissolving fat and organic matter.
MCQ
• ) Which of the following are the recommended heat temperature and
time periods for the moist heat sterilization method used in an
autoclave?
a) 180 c for 5 minutes
b) 121 c for 15 minutes
c) 126 c for 3 minutes
d) 160 c for 45 minutes
 Name the chemical which is an active ingredient of the 'bleach', a
household decontamination product used to kill bacteria, fungi, and
viruses?
a) Sodium chloride
b) Ethylene oxide
c) Sodium hypochlorite
d) Ethyl alcohol
Name the sterilization agent that is most frequently used in hospitals
and clinical laboratories for the heat-labile liquid substances or
antibiotics
a) Dry heat
b) Radiation
c) Filtration
d) Formaldehyde