Sterilization indicators

STERILIZATION
INDICATORS
Mr. Krishnakant B. Bhelkar
Asst. Professor,
Gurunanak College of Pharmacy, Nagpur
Unit II
Pharmaceutical Microbiology
B. Pharm III Semester, (CGBS)

STERILIZATION INDICATORS
Sterilization : It is a process by which an article, surface or
medium is made free of all microorganisms either in vegetative
or spore form.
Sterilization Indicator:
These are the methods to ensure sterilization of any
material, area or surfaces carried out by any of the
sterilization method.
They indicate whether the conditions during sterilization
process were adequate to achieve a defined level of
microbial inactivation.
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Gurunanak College of Pharmacy,
Nagpur

STERILIZATION INDICATORS
Sterilization indicators are divided in three major types:
Physical Sterilization Indicators
Chemical Sterilization Indicators
Biological Sterilization Indicators
Physical Sterilization Indicators uses physical parameters
for the purpose of ensuring the sterility.
Chemical Sterilization Indicators uses various chemicals of
which properties change will tell us about sterilization.
Biological Sterilization Indicators uses various
microorganisms so as to check sterilization.
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Physical STERILIZATION INDICATORS
Physical Sterilization Indicators used for various methods of
sterilization are as follows:
Heat Sterilization:
1. Temperature Record Chart/ Digital Record
2. Thermocouples
Gaseous Sterilization
1. Monitoring of Elevated Temperature
2. Routine Leak Tests (To ensure gas tight seals)
3. Pressure and Humidity Measurement
Radiation Sterilization
1. Plastic Dosimeter (Often perspex)
Filtration Sterilization
1. Bubble Point Pressure Test
2. Checking Integrity of HEPA Filters (DOP Test)
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Heat Sterilization:
1. Temperature Record Chart/ Digital Record
Temperature is measured with thermometer or any digital
device and the graph is compared with master
temperature record.
If temperature record chart is analogous with master
temperature record, this ensures sterilization
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Thermocouple

2. Thermocouples
A thermocouple is an electrical device consisting of two
dissimilar electrical conductors forming an electrical
junction. A thermocouple produces a temperature-
dependent voltage as a result of the thermoelectric
effect, and this voltage can be interpreted to measure
temperature.
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Thermocouple
It is a phenomenon
in which the temperature
difference between the two
different metals induces the
potential differences
between them.

Gaseous Sterilization
1. Monitoring of Elevated Temperature
2. Routine Leak Tests (To ensure gas tight seals)
3. Pressure and Humidity Measurement
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Thermocouple

Radiation Sterilization
1. Plastic Dosimeter (Often perspex)
Example: Thymol blue (TB) solutions and Thymol blue
Polyvinyl Alcohol (TB-PVA) films have been introduced
as Radiochromic dosimeter
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On irradiation with gamma
rays there is bleaching of
Thymol Blue dye.

A forward bubble point integrity test is a procedure which
measures the pressure needed to be applied to the
upstream side of a filter causing bulk or open pore flow
through the largest pores of a wetted filter.
In other words: The bubble point is the minimum gas
pressure required to overcome the surface tension
holding a wetting fluid in a membrane filters
largest pore.
For details please go through
https://wine.appstate.edu/sites/wine.appstate.edu/files/Bub
ble%20Point%20Test.pdf
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Bubble Points for typical wine filter (air as the test gas):
If the recorded pressure is greater than or equal to the
minimum expected bubble point listed above, the filter is
integral.
If the recorded pressure is lower than the minimum bubble point
listed above, the filter has failed the integrity test. Filter Grade
Wetting Fluid Minimum Bubble Point XL II .65 Membrane Water
19 psig XL II .45 Membrane Water 26.1 psig
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Filter Grade Wetting Fluid Minimum Bubble Point
0.65 μm Membrane Water 19 psig
0.45 μm Membrane Water 26.1 psig

2. Checking Integrity of HEPA Filters
(DOP (Dispersed Oil Particulate) Test)
DOP, or filter integrity, testing is the process in which the
integrity of your HEPA (High Efficiency Particulate Air) or ULPA
(Ultra Low Penetration Air) filter is tested through the introduction
of particulates.
Oil is dispersed as an aerosol into the upstream flow of the
filter media, while the number of particles in the downstream flow
is measured using a calibrated photometer.
DOP or Dioctyl Phthalate is a liquid chemical which produces
mono or poly -dispersed test aerosol of sub-micron particles,
generated to challenge (evaluate integrity) of HEPA filters
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chemical STERILIZATION INDICATORS
These are based on ability of heat, steam, sterilant gases
and ionizing radiation to alter chemical and physical
characteristics of a variety of chemical substances.
Such as: Melting of the compounds
Color change of the chemicals
• Monitor one or more parameters required for sterilization-time,
temp, and sterilant
• can be external and Internal
• give instant results
• indicate proper conditions for sterilization were present
If indicator did not change, do not use
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External Chemical Indicator
• process indicator - autoclave tape
• distinguishes processed from unprocessed medical
devices
• secures pack
• labels pack
Internal Chemical Indicator
•Inside each package, tray or container
•Paper strips or cards
•Validates sterilant penetration
•Colour change strip or moving front format
•Can measure all process parameters (integrators)
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biological STERILIZATION INDICATORS
In biological sterilization indicators bacterial spores are used
to check the sterilization process.
The spores are exposed to sterilization conditions and then
added to media and are incubated.
If there is growth from those bacterial spores, this indicates
failure of sterilization process
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Selection of bacterial spores based on
Endospores, or bacterial spores, are the microorganisms
primarily used in BIs.
They are considered some of the toughest ones to kill.
Additionally, bacterial spores are chosen for a specific
sterilization process based on their known resistance to that
process.
For example, Geobacillus stearothermophilus spores
demonstrate a high resistance towards steam and vaporized
hydrogen peroxide and are therefore used in BIs that monitor
these sterilization processes.
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Method of sterilization and respective microbial spore used
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Microorganism Sterilization Method
Bacillus stearothermophilus
(In sealed ampoules)
Steam sterilization
Serratia marcescens
(0.5 μm)
Filtration sterilization
(0.45 μm)
Brevundimonas diminuta
(0.3 μm)
Filtration sterilization
(0.3 μm)
Bacillus subtilis var. niger Dry heat sterilization
Bacillus stearothermophilus Hydrogen peroxide and
peracetic acid
Bacillus subtilis Ethylene oxide &
Formaldehyde
Bacillus pumilus Ionizing radiation

Advantages:
• Confirms the ability of the
sterilization process to kill microbial
spores
• Large number of spores
• Integrate all the parameters of the
sterilization process
• Most critical test of the sterilization
process
Disadvantages:
The process is time consuming and
needs further incubation
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Sterilization indicators

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