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‫السالم عليكن ورحمة هللا وبركاته‬

sterilization

disinfectant sterilizant sterilization

pdf

Control of Microbial Growth

1) Early civilizations :

 To control microbial growth:

o salting, smoking, pickling, drying, and exposure of food and clothing to sunlight.
Some spices prevented spoilage.

2) In mid 1800s :

o joseph Lister discovered phenol

o he use it to prevent:

 Nosocomial infection “hospital acquired infection” caused death in 10% of

surgeries.
 Up to 25% mother delivering in hospital died due to infection

osmotic pressure

Dr El-Attar Page 1
 phenol joseph Lister

absorption
toxicity
infection phenol

resistant
infection infection

Rate of Microbial Death :

o When bacterial populations are heated

or treated with antimicrobial chemicals
o They usually die at a constant rate “as
growth” “exponentially “

exponential nutrient agar

decline stationary phase plateau
diagram rate rate
count time x
log 102 2 101 log
1000 10,000 104 103
90% 1000 9000 10,000
90%

Dr El-Attar Page 2
 autoclave scale
rate
rate

graph rate
curve arithemetic scale
drop
sterilization
log
graph curve

time expontential

o 1 log decrease = 90% of population killed

o 2 log decrease = 99% of population killed
o 3 log decrease= 99.9% of population killed
o 4 log decrease = 99.99 % of population killed
o 5 log decrease =99.999 % of population killed
o 6 log decrease =99.9999 % of population killed

log
1000 10000 1log 
100 1000 2log 
99% 2log 10,000 1% 100 1000
population
10 90% 100 2log 3log 
0.1% 10,000 10
disinfectant 99.9%

Dr El-Attar Page 3
 Factors affecting antimicrobial effectiveness
:

1. Number of Microbes “bioburden” :

Resistant  Prion
 Bacterial spores
The more microbes present. The more time it takes (most resist)
to eliminate population.  Mycobacteria
 Small non –
enveloped viruses
 Gram –negative
2. Types of microorganism present : bacteria
 Fungi
 Some chemicals have a different effect  Large non-
depending it the organism is Gram-positive or enveloped viruses
 Gram – positive
Gram-negative bacteria
 Some organisms intrinsically more resistant to Susceptible
 Lipid enveloped
viruses
disinfectants
a) Mycobacterium spp
b) Pseudomonas aeurginosa.
 Bacterial endospores are more resistant to heat treatment
 Cysts of Giardia intestinalis more resistant to chlorine used in water treatment

antimicrobial
antimicrobial agent
mycobacterium spp
disinfectant pseudomonas aeurginosa
Giardia intestinalis cysts microorganism
spores
sterilization heat
prion metabolites microorganism
spores nervous system
sterilization
envelope mycolic acid mycobacteria
heat lipid enveloped virus non- virus
lipid envelope

3. Phase of growth:

Actively growing cells more susceptible to chemical disinfectants than stationary

phase organisms

4. Use of an appropriate biocidal agent

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 phase of growth disinfectant

biocidal agent pseudomonas aeurginosa

pseudomonas Cetrimide agar
antiseptic aeurginosa
pseudomonas aeurginosa
Cetrimide pseudomonas aeurginosa

5. Physical and chemical factor of biocidal agent :

These include temperature. pH, relative humidity and water hardness.

o Generally the activity of most biocides Increases as the temperature increases.

There is a point at which the chemical degrades if heated too much.
o An increase in pH improves the antimicrobial activity at some agents as with
glutaraldehyde but decreases the activity of others such as hypochlorites. This
effect is caused either by alteration at the germicidal molecule or the cell surface
of the microorganism.
o Relative humidity influences the activity at gaseous agents such as ethylene
oxide.
o Water hardness reduces the rate at killing of some biocides because formation of
insoluble precipitates.

temperature pH antimicrobial agent

biocide water hardness
limit
pH disinfectant structure
glutaraldehyde antimicrobial agent
relative humidity pH
sterilization
nucleic acid ethylene oxide
alkylation
disinfectant
effect insoluble

Dr El-Attar Page 5
6. Concentration of biocidal agent

7. Effective contact time at the agent with all surfaces to be treated:

there is an exponential relationship between the number of organisms kited and the
time taken to kill them.

8. Organic matter :

 As serum, blood, pus or fecal material. They may interfere “chelation” with the
activity of biocides in at least two ways
 a chemical reaction between the biocide and the organic matter may result in a
complex that is less germicidal or non-germicidal leaving less of the active agent
to attack the microorganisms .
 Organic material may protect microorganisms from attack by acting as a physical
barrier. This is another reason for the cleaning of objects before any sterilization or
disinfection procedure.

serum pus organic matter disinfectant

biocide chelation

9. Biofilms:

 The production of thick masses of cells and

extracellular materials or biofilms can protect
microorganisms from the cidal action of
biocides. Biofilms are microbial masses
attached to surfaces that are bathed with
liquids.
 A biocide must saturate or penetrate the
biofilm matrix before it can kill the microorganisms within it
 Biofilms can form on surfaces of endoscopy equipment and in the tubing of
automated washer/disinfectors as well as on water filters, housings and pipes thus
protecting the embedded organisms from exposure to biocides and serving as a
reservoir for continuous contamination.
 E.g. staphylococcus aureus & pseudomonas aeurginosa

Dr El-Attar Page 6
 biofilm biofilm
biocide
urinary system trachea
pseudomonas aeurginosa staphylococcus aureus biofilm
biofilm
matrix
nucleic acid exopolysaccharide
exopolysaccharide
 biofilm

Cleaning :

It is important method for two reasons:

1. it is a method of decontaminating low-risk items

2. Prior to disinfection or sterilization processes.

o Many pieces of equipment classed as low risk can be safely decontaminated

between patients by this method.
o Detergent is essential for effective cleaning. It breaks up grease and dirt and
improves the ability of water to remove soil
o Around 80% (1log decrease) of microorganism will be removed during cleaning.
However. drying the equipment afterwards is very important to prevent any bacteria
that remain from multiplying.

decontamination
cleaning organic matter
low – risk item 

sterilization 
spores disinfection

Dr El-Attar Page 7
 1log
sterilization

Sterilization :

o Killing or removing all forms of microbial life (including endospores) in a material or

an object
o Heating is the most commonly used method at sterilization .
o A sterile product is the one that does not contain any living organisms.

spores sterilization
sterile product
metabolites microorganism

Disinfection :

 Reducing the number of pathogenic microorganisms to the point where they no

longer cause diseases. Usually involves the removal of vegetative or non-endospore
forming pathogens
 Acceptable reducing no. of microorganism (3log reduction: 5 log reduction)

 Items in hospital classified into:

1. High risk items. i.e enter the body
2. Intermediate risk items .i.e. contact the skin
3. Low risk items .e.g. beds,floors …etc

Lo
vegetative bacteria disinfection
5log 3log reduction spores
categories items
High risk items category 
sterile
Intermediate risk items category 

Dr El-Attar Page 8
 Low risk items category 

1. Which of the following is the most resistant to antiseptic / sterilization ?

a. Fungus
b. Cyst
c. Prion
d. Bacterial spores

2. The absence of all forms of microbial life, including spores, is known as

a. Sanitization
b. Disinfection
c. Decontamination
d. Sterility

1 2
c d

Dr El-Attar Page 9
 o 1. Sterilization :

Definition :

Killing or removing all forms of microbial life (including endospores) in a material or an

object

Application of sterilization :

1) parenteral administration
2) ophthalmic product
3) let contact with broken skin.
4) Mucosal surfaces or internal organs.
5) soiled dressings and other contaminated items is necessary to minimize the health
hazard associated with these articles.

 Sterilization processes involve the application of:

 a biocidal agent or any physical process to a product or preparation with the aim of
killing or removing all microorganisms.
 These processes may involve elevated temperature, reactive gas, irradiation, filtration
through a microorganism- proof filter.
 The success of the process depends upon a suitable choice of treatment conditions.
E.g. temperature and duration of exposure.
 With alt articles to be sterilized there is a potential risk at product damage which for a
pharmaceutical preparation may result in reduced therapeutic efficacy. Stability or
patient acceptability.
 Thus. There is a need to achieve a balance between the maximum acceptable risk of
failing to achieve sterility and the maximum level of product damage that is
acceptable.

sterilization
circulation sterilization
tetanus spores dressing

sterilization
sterilization pore size filter
reactive gas suspension

Dr El-Attar Page 10
 microorganism free product
sterilization
sterile balance thermostable

 The British pharmacopoeia (I993) recognizes five methods for the sterilization of
pharmaceutical products:

1. Dry heat.
2. Moist heat.
3. Gamma or electron radiation.
4. Filtration through a bacterial filter.
5. Ethylene oxide

pharmacopoeia sterilization 

dry heat heat

moist moist heat
latent heat steam penetration power
radiation steam

filtration radiation
suspension solution
ethylene oxide reactive gas

What to be considered when designing a sterilization protocol ?

 Practically, it depends on the "bioburden", in C.F.U.

 We assume that the organisms present in any load will not be more resistant than
the most resistant bacterial Spores.

 Marker (reference or indicator) organisms:

 Bacillus stearothermophilus for moist heat

 B. subitis or clostridium tetani spores for dry heat.
 B. pumilus spores or Micrococcus radiodurans for ionizing radiation.
 B. globigii (and special strain of B. subtitis) spores for gaseous sterilization.

Dr El-Attar Page 11
 sterilization
Bacillus sterilization
B. subitis 110 moist heat stearothermophilus
B. pumilus spores dry heat clostridium tetani spores
B. B. globigii ionizing radiation Micrococcus radiodurans
spores gas sterilization sterilization subtitis
sterilization spore
marker reference organism
sterilization

Survival curves :

When exposed to a killing process, populations of

microorganisms generally killed in an exponential fashion.
Independent of the initial number of organisms.

Type A curve :

 is approximately linear over the whole time range.

Type B curve :

 exhibits an initial plateau, before assuming a linear form, or a shoulder as in case of

some spores of low germination index.
 This is the example of B. stearothermophilus. Which may be activated by heat
increasing their viable count during the initial periods of heating.

Type C curve :

 is biphasic, showing a reduced rate of kill at low survival levels.

 The death of microbial populations exposed to lethal temperatures follows the
kinetics of first order reactions

[LogNo-LogNt] t
k'= D = 1/K' =
t [LogNo-LogNt]

Dr El-Attar Page 12
 exponential
sterilization

linear A 
spores B 
B. stearothermophilus

curve biphase C 
first order kinetic
Nt
No zero time initial bacteria
time
90% 1log K' 
D-value

Expressions of resistance :

These expressions can give a little indication about the relative sensitivities of different
Organism

1) Thermal death point (TDP):

 Temperature required to kill all microorganism in a suspension within a certain time.

 This definition ignore :
a) Temperature coefficient .
b) Physiological status
c) Nature of the environment

2) Thermal death time (TDT):

1.

 Extinction of Exposure time

 The shortest time required to kill all microorganisms in a suspension at a
predetermined temperature

Dr El-Attar Page 13
 3) D- value:

The decimal reduction time (D): is the time, in minutes, taken

at a fixed temperature (or the radiation dose) required to
reduce the number of viable organism by 90% (1log)

4) Z –value :

is the increase in temperature needed to reduce the D-value

of an organism by 90% or to produce a decrease of one log
cycle on the log 10 D-value/temp plot.

For moist heat sterilization the z-value of:

 B. stearothermophilus spores, as a marker organism. have a

mean z-value of 10°C.
 dry heat , B.subtitis spores have a mean of about 22°C.

thermal death point (TDP) 

temperature coffiecient
sterilization
thermal death time 

90% D-value 
1log 1log
90% z-value 
90% D- value z-value
D-value Z-value

Dr El-Attar Page 14
 Sterility assurance :

Since sterility is on absolute term (there are no degrees of sterility) therefore, there are no
levels of contamination which may be considered negligible or insignificant and
therefore acceptable.

What is Sterility assurance or o microbial safety index?

 It is an index that gives a numerical value to the probability of a single surviving

organism remaining to contaminate a processed product.
 For pharmaceutical products. the sterility assurance accepted as one in one
million units processed

sterilization protocol necessary to achieve this, with any given organism of known D-
value. can be established from the inactivation factor (IF):

IF =N0/ N IF = 10t/D

 t = Contact time (tor heat or gaseous sterilization) or dose (for Ionizing radiation).
 D = the D-value (appropriate to the process employed).

For an initial burden at 102 spores on Inactivation factor of 108 will be needed to give the
required sterility assurance of 10-6 this will require exposure of the product to eight times
the D-value of the reference organism (8D)

sterilization sterility assurance

sterile sterile sterilization
absolute sterility sterile product
batch sterile term

inactivation factor sterilization

killing
D- D contact time t t/D 10
sterilization 102 MCQ value
102 10 -6 sterilization
8 t/D 10t/D IF 108 10-6
 t/D = 8
 t= 8D

8D-value sterilization

Dr El-Attar Page 15
 Physical Methods of Microbial Control :

1) Heat :

Heat kills microorganisms by denaturing their enzymes and other proteins. Heat
resistance varies widely among microbes.

A) Moist heat b) Dry heat

Mechanism of action Coagulation & denaturation Oxidation
121oc for 15 min
Temperature & time 160oc for 2hrs
135oc
Pressure 15 psi -

moist moist heat sterilization 

denaturation coagulation mechanism
135 15 121oc
15 psi pressure

oxidation dry heat 

160 sterilization

 Choose the correct answer:

1) Which of the following microorganisms is used to biologically monitor the dry heat
sterilizer
a. Bacillus atrophaeus
b. Geobacillus atrophaeus
c. Bacillus subtillis
d. Bacillus stearothermophilus

1
c

Dr El-Attar Page 16
 Stages of sterilization :

Stages Characters

 1st stage "Heating up: Articles must first be raised to sterilization temperature

is the recommended sterilization time during which the

 2nd stage "Holding time":
recommended sterilization temperature is maintained.
During which temperature decrease to room
 3rd stage "Cooling down" :
temperature (ambient).

 In order to calculate the most appropriate condition for each stage, a method has
been used to convert all the temperature time combinations, occurring during the
heating-up. Sterilizing and cooling stages of a moist heat (steam) sterilization cycle.
to the equivalent time at 121°C.
 Using this approach the overall lethality of any process can be deduced and is
defined as the F-value which expresses heat treatment at any temperature as equal
to that of a certain number of minutes at 121°C.
 The F-concept permits calculation of the extent to which the heating and cooling
phases contribute to the overall killing effect of the sterilization cycle so that the
holding time may be reduced (below 15 minutes at 121°C) without reduction at
sterility assurance and this enables a sterilization places to be individually developed
for a particular product to prevent over-processing of thermolabile products

autoclave
curve heating up
curve sterilization holding time
sterilization
curve cooling down sterilization
holding time
sterlization
F-Value
holding sterilization holding time

Dr El-Attar Page 17
 product sterilization time
thermolabile product holding time

a) Moist Heat :

 as microorganisms by coagulating their proteins

 in general. Moist heat is much more effective than dry heat

 Types of moist heat:

a) moist heat below 100oc

b) Moist heat at 100oc
c) Moist heat over 100oc

more effect moist heat sterilization

penetration moist dry heat
100 
100 
100 

Moist heat below 100°C sterilization

1. Moist heat below 100°C:

For substances damaged by heat over 100°C.

a) Heating with bactericide :

 It is chemical sterilization in which heating below 100°C is recommended

 e.g., 0.002% phenyl mercuric nitrate or 0.2% chlorocresol

100

phenyl sterilization
0.2% chlorocresol 0.002% mercuric nitrate
disinfactant

Dr El-Attar Page 18
 Chemicals must be :

 non toxic
 heat stable
 non – volatile
 compatible with the ingredient

 Limitation :

 Not for oily preparation : chemical are active in water and oil reduce activity
 Not used when the dose exceed 15 ml, it may cause toxicity
 Not for intrathecal intracisternal or other sensitive tissue, to avoid irritation and
damage

volatile thermostable toxic

compatible
active oily preparation
preparation activity water
toxicity 15 emulsion
preparation sterilization
spinal cord

b) Tyndalization:

 Tyndalization (fractional steam sterilization):

 a process that kills spore- forming microorganisms , involves exposing the material
to elevated temperatures (killing the vegetative cells) , the incubation at 37oc (to
allow spores to germinate to form new vegetative cells ) and the exposure to
elevated temperature again (to kill the newly germinated particularly resistant
endospores
 heating Less than 100oc for 30 min then incubating at 37oc for 3days
 It is not sterilization
 Used for culture media containing sugar or gelatin

culture media tyndalization

culture spore
media
spore incubation agar
vegitative cells vegitative

Dr El-Attar Page 19
 spores agar
metabolite sterilization

c) inspissation:

as in tyndalization, but heating:

 at 80oc for 1hr for first day

 at 80oc for 20 min for 2nd & 3rd days

it is not sterilization (it is consider decontamination process)

use : culture media containing egg or serum

inspissation

decontamination sterilization
serum culture media
structure

D ) Pasteurization :

Is a preservation rather than sterilization method, used to improve the keeping

properties

 Microorganisms in milk

1) Tuberculosis
2) Brucella
3) Salmonella
4) Streptococci
5) Poliomyelitis

Used for sterilization of milk , wine ,juice …etc

pasteurization
spores sterilization
salmonella Brucella Tuberculosis
poliomyelitis streptococci

Dr El-Attar Page 20
 The main methods are:

 Holding method: heating of about 62°C/30 min then sudden cooling to 7°C.
 Flash method: heating at about 72°C/15 seconds or 82°C for few seconds then
rapid cooling to 4°C

The method Holding method Flash method

Procedure 62oc , 30 min then 7oc 72oc , 15 sec then

Picture

holding method
flash method
15

F) Heat killed vaccines :

Bacteria are killed using temperature just sufficient to kill but keep its antigenicity

vaccine

2. Moist heat at 100°C :

 boiling or steaming at 100°C kill most vegetative bacteria within 5-15 mm.
 but not bacterial endospores require up to 26 hrs. to be killed
 2 % sodium carbonate prevents rusting
 Uses: In emergency for sterilization of glass syringes other surgical instruments

Dr El-Attar Page 21
 moist heat at 100oc
spore vegetative

3. Moist heat over 100oc :

 Water or steam under pressure

 Example :

1. Pressure cooker
2. Autoclave

 Advantages of Steam:

1. Excellent medium for heat transfer

2. High latent heat, high specific heat
3. High penetration power
4. Uniform temperature, rapid heat –up of objects

 Specific heat : energy required to change a unit mass of a material by 1oc , unit
calories
 Latent heat: energy required to change the state (gas, liquid, solid) of a unit mass of
material
 Transfer energy:When saturated steam comes in contact with the cooler surface of
steamed articles, it condenses and an amount of latent heat is transferred

Condensation and heating continue (because when it condenses, the space is replaced
by fresh steam until the article reaches the sterilizing temperature needed

100 sterilization
steam
autoclave
steam steam
latent heat steam

specific heat

Dr El-Attar Page 22
 penetration power steam

specific heat
latent heat
transfer energy

autoclave
autoclave

Temperature/pressure relationship of the steam :

 The relation between boiling point and the pressure

recorded in kg/cm2 above atmospheric pressure is given In
the following phase diagram
 If water is boiled in a closed vessel and air was removed out
of the vessel before it is closed , the pressure rise and the
temperature of the water, and its steam , will rise above the
normal boning point i.e. above I00°C.
 Saturated steam is formed only on the phase boundary (boiling point curve) where
steam and water are in equilibrium.
 It condenses easy and is source of heat and moisture

penetration sterilization steam

latent heat spores spores cortex

pressure steam
pressure
air steam steam autoclave
autoclave autoclave autoclave
100 steam
water vapor water equilibrium saturated steam
steam water vapor
sterilization latent heat
Dr El-Attar Page 23
 o Saturated steam :

 Saturated steam may be:

1. Dry saturated steam (free from water droplets).

2. Wet saturated steam loaded with suspended tiny water droplets. It might cause
excessive wetting of the sterilized material.

However, droplets can be removed efficiently by using water separator baffles located
at the immediate entry site of steam into a sterilization chamber.

dry saturated steam saturated steam

dry wet
contamination sterilization
steam autoclave autoclave
steam water droplet
baffles wet saturated steam
dry saturated steam
steam baffles

o Super -heated steam :

o

 Super -heated steam is formed if the temperature of a dry

saturated steam increased at constant pressure, the degree
of saturation is decreased the steam becomes superheated.
 Super –heated steam has a temperature higher than it
supposes to carry at specified pressure (above the boundary)
, So that , it does not condense easy and is not suitable for
moist heat sterilization being source of heat and not moisture
i.e. act as a hot air.
 Steam pressure may be measured in atmosphere/cm2 or
kg/cm2 or pounds/square inch (psi).
 One of atmosphere/cm2 =one kg/cm 2 = about 15 pounds/I2

autoclave
super-heated steam water vapor steam
water vapor saturated steam
sterilization steam saturation

Dr El-Attar Page 24
denaturation mechanism of action dry heat moist heat
dry heat sterilization oxidation
steam pressure
15 psi 15 pounds/I2 one kg/cm 2 atmosphere/cm2

 Choose the correct answer:

1. measurement for moist heat sterilization:

a. 160oc / 2hrs
b. 142oc/15min/15psi
c. 121oc/15min/15psi
d. 121oc/15sec/15psi

Equipments are used in moist heat sterilization :

a) Pressure cooker :

 It is a steel vessel having a lid that can be secured tightly by

heavy clamps and provided with air vent and safety value.
 A temperature of 113- 121°C could be attained and used for 20-25 min.

 It is used in emergency to sterilize:

1. Infant 's diet bottles

2. surgical tools for minor operations

moist heat sterilization 

pressure cooker autoclave pressure cooker

Dr El-Attar Page 25
 pressure cooker
113 sterilization
pressure cooker 121

b) Autoclave (Steam Sterilizer) :

 is the most widely applied sterilization equipment in laboratories.

hospitals and industry.
 It may be considered as a large pressure cooker the articles are not
placed in water but suspended in sterilization chamber on steam
under pressure.

 Design:

 The source of steam could be either from:

a. boiling water in the bottom of the vessel

b. coming through pipes from a separate boiler the autoclave.

It is also provided with air vent, safety value and controls for temperature, pressure, air

 Types:

1. Vertical or horizontal.
2. Cylindrical or rectangular, most modern autoclave are rectangular to allow full
utilization of the space.
3. Jacketed or non-jacketed.
4. Portable & stationary

pressure cooker autoclave autoclave

sterilization steam sterilization
chamber steam steam
water baffles autoclave steam
air vent autoclave dry steam droplet
water vapor autoclave
dry heat sterilization moist heat serilization
safety valve
autoclave

Dr El-Attar Page 26
 horizontal vertical
cylindrical rectangular
jacket jacketed
stationary portable jacketed

Jacketed autoclave :

 Perforated shelf helps in steam

distribution

 Safety valve controls the pressure that

control the temperature

most autoclaves have a steel jacket (double- walled) to possess the following advantage:

 Rapid re-operation .
 May help in the drying of wet loads .

chamber steam autoclave

autoclave air valve autoclave
steam autoclave steam steam
autoclave 15psi
perforated shelf safety valve
sterilization autoclave steam
flask flask flask

jacketed double wall autoclave

sterilization
water autoclave sterilization
autoclave droplet

Dr El-Attar Page 27
 Difference between portable & stationary autocalve :

Portable Stationary

1) Movable ( self contained with steam 1) Fixed (connected to steam pipe

generated inside ) . coming from a distant boiler) .
2) Vertical 2) Usually horizontal .
3) Economic in small scale 3) Economic on large scale (one boiler
4) May be nonjacketed supply several autoclaves) .
5) Usuaily smaller 4) Usually jacketed .
6) Never super heated (steam in contact 5) Usuatlly larger.
with water ) . 6) May be super heated

autoclave
autoclave portable 
superheating jacket
autoclave
staionary 
chamber superheating jacketed horizontal
steam

Causes of superheating :

1) Contact of saturated steam with overheated surface such as autoclave jacket.

2) In sterilization of dry fabrics such as cotton and linen
3) Detective reducing valve
4) The presence of air

jacket saturated steam superheating

superheating autoclave
air saturated steam criteria
superheating autocalve

Dr El-Attar Page 28
 Why air is removed ?

1) It causes super heating

2) It reduces penetration of steam inside porous materials.
3) the sterilizing temperature may not be reached and heating up period get longer.
4) In presence of air, more heat is required to reach the same temperature ie., less
economic.
 Air is removed through the air ejector valve as jets of mixed air and steam until
complete displacement of air occur or by using vacuum pump before introducing
the steam to the chamber (prevacuuming) .
 The best method of drying of the load is to release the steam from air vent so that the
pressure decreases rapidly to zero while temperature still above 100°C allowing rapid
evaporation of water.

autoclave
steam pentration power superheating
steam sterilization

air ejector valve autoclave

autoclave steam
air vent sterilization
autoclave product

Examples of autoclaves :

a) Dressing autoclave :

Horizontal , with double doors , one for loading and one for
unloading into separate clean area

 Precaution:

 Ultra high temperature sterilization at 134oc/ 3min is

performed , to avoid change of color .
 Never allow superheating ,which cause charring
 Load must be obtained dry " because wet load are more susceptible to
recontamination".
 In addition to the pressure gauge , thermocouples are provided to detect
superheating

Dr El-Attar Page 29
 dressing autoclave autoclave
horizontal dressing
dressing
steam 134
superheated saturated steam
recontamination autoclave
temperature pressure measurement
sterilization superheated steam
sterilization incubator nutrient broth
turbidity

b) Bottled fluid sterilizer :

 Precaution :

1. Small sealed containers e.g. ampoules :

 Must be aqueous and not completely filled to allow generation of steam

without cracking " steam will not penetrate inside of the ampoule"

2. Large aqueous glass bottles, transfusion bottles :

 Must be partially evacuated to prevent cracking

3. Flexible aqueous plastic container :

 Cannot be evacuated thus proportion of air is left inside the autoclave to

compensate between the pressure inside and outside the container to avoid
bursting

bottle bottled fluid sterilizer

contamination

sterilization steam steam

ampoule steam
bottle sterilization steam

Dr El-Attar Page 30
 autoclave autoclave
MCQ moist heat sterilization


 Choose the correct answer :

1. moist heat sterilization kills microorganisms by disrupting and altering the

structures of their proteins. What is this process called?

a) Denaturation
b) Sanitation
c) Oxidation
d) Hydrolysis

Mechanism :

dry heat kills by oxidation effects .

Types :

1) Direct flaming :
 used to sterilize inoculating loops and needles .
 heat metal until it has a red glow .

2) Incineration :
 effective way to sterilize disposable items ( paper cups , dressing ) and biological
waste .

3) Hot air sterilization :

 Place objects in an oven .
 Require 2 hours at 170oC for sterilization
 Dry heat transfers heat less effectively to a cool body than moist heat .

4) Infra- red tunnel .

Dr El-Attar Page 31
 dry heat dry heat sterilization
oxidation mechansim

falme loop direct flaming

incineration
hot air sterilization
sterilization dry heat 170oC
latent heat moist heat moist heat
infrared
product

1) Direct flaming :

 Flaming the loop helps to prevent contamination of the bacteria .

 When flaming the loop , make sure that all of the wire has been heated
to redness .

loop direct flaming

loop loop
sterilization
2) Incineration :

 Burns and physically destroys organsims

 Used for :
a) Needles .
b) Inoculating wires
c) Glassware
d) Body parts

inceration
infectious bacteria glassware loops

Dr El-Attar Page 32
 3) Hot air oven :

 It consists of insulated stainless steel camber with perforated shelves

 Electrically heated by coils arranged in all sides except the door
and thermostatically controlled
 Heat is transferred from the source to the article by:
1. Conduction
2. Radiation
3. Convection
 However, convention is more important and is the main method of heat transfer
 Air is circulated with a fan to maintain high and uniform temperature

mechanism of action dry heat sterilization

oxidation
coils
convention

 Precaution :

1. Items should not be placed compact over the perforations

2. Items that resist heat transfer e.g. powder, should be placed in shallow layers
3. Items that allow convection of heat e.g. oils are sterilized in bulk
4. Items to be sterilized are located at room temperature and removed at 40oc to
avoid cold shock and cracking of glass

hot air oven

powder
talc
bulk convention
40

 Recommened temperature :
 B.P : 150oC / 60 mn for medication and 160oC / 60mn for glass .
 USP : 160oC / 60 mn for medication and 170oC / 2hrs for glass .

hot air oven

Dr El-Attar Page 33
 160 150 british pharmacopaeia

Unites states pharmacopaeia

170 glassware 160

 Application :

1. Glassware (beakers,tubes, …etc)

2. Porcelain ( mortar , pestle …..etc)
3. Metals (forceps, scissors…etc)
4. Fixed oils ,liquid,soft and hard paraffin ,woolfat,wool,alcohols,wax, glycerin
5. Powder: talc,kaolin,sulphonamides, starch and lactose
6. Paraffin gauze ,cat gut ,silicon rubber

dry heat application

fixed oil test tubes glass ware
powder forceps

4) Infra- red tunnel :

 Example of continuous sterilization

 An insulated tunnel constructed bet aseptic area & normal area
 It is consider dry heat sterilization " not radiation sterilization"

 This tunnel contain:

1. IR lamps (λ=700-950 nm) fixed in the ceiling and more concentrated in the entry to
shorten the heating up time
2. Metal conveyer belt moving at constant speed and on which articles to be
sterilized are loaded . the articles are heated up then exposed to sterilizing dose
before colling , to be received ready for aseptic filling in the asptic area .

 Uses:

1. Dark colored containers

2. Ampoules or vials

Dr El-Attar Page 34
 infra-red dry heat sterilization
IR tunnel 700-950 nm IR

radiation sterilization dry heat IR IR

radiation ampoules
heat sterilization

Dr El-Attar Page 35