Sterilization : Sterilization Muraleedharan CV
Division of Artificial Organs
Biomedical Technology Wing
SCTIMST, Trivandrum, INDIA Agenda : Agenda Basics
Validation Disinfection or Sterilisation ? : Disinfection or Sterilisation ? What is the temperature needed to inactivate bacteria ?
It depend on the bacteria because some are highly resistant to heat.
(Ex.: Geothermal bacteria like hot spring bugs withstand 250 oC )
Most human pathogens were thought to be killed by temperature lower than 150 oC. Disinfection may be defined as: Cleaning an article of some or all of the pathogenic organisms which may cause infection STERILISATION is a process by which living organisms are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate Nature of the problem : Nature of the problem Medical devices and appliances that contact blood or other internal tissues are expected to be sterile.
Many medical practitioners advocate an absolute concept for sterility to mean the lack of any viable microorganisms on or within the device and the interior of the packaging
Most technologists operate from the stand point that sterility of medical product is a probabilistic function. Definitions : Definitions STERILISATION is a process by which living organisms are killed or removed to the extend that they are no longer detected by standard culture media which have previously been found to proliferate.
STERILISATION is a process by which anticipated levels of microbial contaminants (bioburden) in a load of items are exposed to that lethality of sterilising condition, so that the probability of survivor per item (PSI) is less than a specified value. Effectiveness of sterilization : Effectiveness of sterilization ? Initial bioburden in the load
? Lethality of the sterilising condition
Duration of process
Steam - Temperature / pressure
ETO - ETO Concentration, Temp, %RH
Radiation - Dosage rate
Chemical - Concentration, Temperature Sterility Assurance Level (SAL) : Sterility Assurance Level (SAL) Expressed either as Probability of Survivor per Item (PSI) or as Microbial Survivor Index (MSI)
PROBABILITY OF SURVIVOR PER ITEM (PSI) : PSI of 10-6 indicates that One in a million packages can contain one viable microorganism after sterilisation
MICROBIAL SURVIVOR INDEX (MSI) : MSI is derived by taking the reciprocal of the logarithm of PSI
Different devices may require different levels of Sterility Assurance Levels Process Design : Process Design Max. Bioburden in the load = 106 CFU per pack
SAL required (PSI) = 10-6
Load pre-warming period = 30 minutes
Post flushing period = 90 minutes
D-Value = 2.5 minutes
Total exposure duration required = 12 x D minutes = 30 minutes(6D for reducing the bioburden to unity and 6D for attaining PSI of 10-6)
Total process duration = 30 min + 30 min + 90 min = 150 minutes Sterilization Techniques : Sterilization Techniques Steam
.. Steam : Steam Most reliable and practical
Rapid acting sterilant
Factors influencing the process(Temperature, time , penetration)
Standard cycles 121°C / 15 psig; 20-30 minutes132 °C / 28 psig; 5-10 minutes
High temperature (polymers)
large thermal cycling (polymers)
Drying / Handling Dry heat : Dry heat Suitable for metallic / ceramic devices
High temperature process
Factors influencing the process(Temperature, time)
Standard cycles 160°C ; 1 - 2 hours180°C ; 30 - 45 minutes
Slow ETO : ETO Economical and popular
Low temperature process
Factors influencing the process(ETO Conc., temp., %RH, time)
Standard cycles 600 mg/L ETO, 60% RH, 55°C, 2 Hours(100 % ETO / ETO-Freon / ET-CO2 mixtures)
Formation of EG / ECH
Long aeration cycles Radiation : Radiation Most reliable and effective
Excellent penetrating power
Factors influencing the process(Energy level, time)
Radiation sources Gamma (Co-60, Ce-137), Beta (Electron accelerateors)
Dosage Levels1 Mrad for MSI = 3,
1.6 - 2 Mrad for MSI = 6Normally used max dosage = 2.5 Mrad
ShortcomingsLarge initial investment, Not suitable for many polymers Chemicals : Chemicals Formaldehyde solution / vapour
Ethylene oxide solution
. . Plasma : Plasma Glow discharge plasma (low temp.)
Hydrogen peroxide precursor
Free radicals and ions interact withliving organisms and destroys them
Ideal for industrial applications
Penetration of precursor is critical
Minimal residuals as very low concentration are used
Cleanliness of the device / package is critical Pulsed Light : Pulsed Light Wide spectrum pulsed light
Ultraviolet to infrared
20,000 times brighter than sunlight
0.1 to 2 J/cm2 energy levels per flash
1 to 12 J/cm2 energy dosage levels
Very fast and economical
Ideal for transparent packaging
Not fully evaluated for material damage STERILISATION VALIDATION : STERILISATION VALIDATION Installation qualification
Indicators are used for process validation as well as process monitoring Chemical Indicators (CIs) : Chemical Indicators (CIs) Except for wax, most CIs are based on a pH change resulting from organic acid evaporation by heat and revealed by a colorimetric indicator
The oldest CI
Pb + S + H PbS
The reaction do not occur without heat Indicators : ISO Class 11140-1 : Indicators : ISO Class 11140-1 Class 1 : External indicator charged to signal if the pack has been exposed or not.
Example : autoclave tape.
Class 2 : Indicator for a specific parameter - Qualitative
Example : Bowie Dick (vaccum à 121 oC) Before Use Incorrect Change Correct Change Indicators : ISO Class 11140-1 : Indicators : ISO Class 11140-1 Class 3 : Indicator for a unique parameter - Quantitative
Example (s) :
Melting wax pellet at 121 oC
Colour change crayons
Mostly used for validating temperature distribution in steam sterilisation chambers. Indicators : ISO Class 11140-1 : Class 4 : Indicator sensitive to 2 parameters (ex.: time and temperature) within 25 % of expected targets.
For class 4 and higher, indicators must change abruptly
The change of color must happen within 25 % of the expected time and within 2 oC
Example : An indicator that accept (OK or Pass) at 132oC pour 4 min. MUST reject (Fail) a 130oC for 3 minutes. Indicators : ISO Class 11140-1 Indicators : ISO Class 11140-1 : Class 5 : An indicator / integrator sensitive to 2 or more parameters, and reacting within 15 % of expected targets.
In this category, the change of color must be abrupt, happens within 15 % of expected targets and MUST NOT happen if the targeted temperature is not achieved within 1oC.
Example : An indicator that accept (OK or Pass) at 132oC for 4 min MUST reject (Fail) a 131oC for 3 minutes and 22 seconds. Indicators : ISO Class 11140-1 Indicators : ISO Class 11140-1 : Classe 6 : An indicator / integrator sensitive to 2 or more parameters, and reacting within 6 % of expected targets.
In this category, the change of color must be abrupt, happens within 6% of expected targets and MUST NOT happen if the targeted temperature is not achieved within 1oC.
Example : An indicator that accept (OK or Pass) at 132oC for 4 min MUST reject (Fail) a 131oC for 3 minutes and 45 seconds. Indicators : ISO Class 11140-1 Biological Indicators : Contains specific bacterial spores with known concentration, with or without culture media
Bac. Subtilis var. niger
Bac. pumilus Biological Indicators Slide 25: Thank You