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Department of Pharmaceutics
R.C. Patel Institute Of Pharmaceutical Education and Research
• Culture Media and Incubation Temperature
• Growth Promotion and Method Validation /
Method Suitability Test
• Number of Articles and volume to be tested
• Test Method
• Observation and Interpretation of Results
• Essential thing to know regarding Sterility
What is sterility Testing?
• A test conducted to ensure the batch of products is sterile or has been
sterilized, meaning free of viable micro organisms ( Bacteria, yeast or
• Sterility testing is qualitative test which reveals quality of samples
• Sterility testing of medical devices is required during the sterilization
validation process as well as for routine quality control.
The test is applied to substance, preparations, or articles which
according to pharmacopeia are required to be sterile. However, a
satisfactory results only indicated that no contaminating microorganism
has been found in the sample examined under the conditions of the test.
• Sterility testing is a very tedious and artful process that must be
performed by trained and qualified laboratory personnel.
Culture Media and Incubation Conditions
→ Fluid Thioglycollate Medium (FTM) and incubation temperature is
30⁰ to 35⁰C for 14 days.
→ Soybean-Casein Digest Medium – (SCDB) and incubation temperature is
20⁰ to 25⁰C for 14 days.
Fluid Thioglycollate Medium (FTM)
Ingredients Amount Significance
L-Cystine 0.5 g
Reducing Agent, prevent accumulation of
Peroxides which are lethal to some
Sodium Chloride 2.5 g Osmotic Balance
Monohydrate/Anhydrous 5.5/5.0 g Energy Source
Agar 0.75 g
Prevent rapid uptake of Oxygen and helps
to maintain anaerobic environment
Yeast Extract (water-soluble) 5.0 g Growth Factor
Pancreatic Digest of Casein 15.0 g Growth Factor
Sodium Thioglycollate 0.5 g Reducing agent, remove Oxygen
or Thioglycolic Acid 0.3 mL
Resazurin Sodium Solution
(1in 1000), freshly prepared 1.0 mL
Redox Indicator, red in oxidized state and
colourless under anaerobic conditions
Purified Water 1000 mL pH – 6.9 to 7.3
Soybean-Casein Digest Broth (SCDB / TSB)
Ingredients Amount Significance
Pancreatic Digest of Casein 17.0 gram Provide Nitrogen, Vitamins
Papaic Digest of Soybean Meal 3.0 gram Provide Nitrogen, Vitamins
Sodium Chloride 5.0 gram For Osmotic Balance
Dibasic Potassium Phosphate 2.5 gram Buffering Agent to control
Dextrose Monohydrate / Anhydrous 2.5 / 2.3 gram Energy source to promote
Purified Water 1000 mL pH - 7.1 to 7.5
Diluting and Rinsing Fluids
• Fluid A – 0.1% Peptone water; pH 6.9 to 7.3
•Fluid D – 0.1% Peptone Water with 0.1% Tween 80; pH
6.9 to 7.3
• Fluid K ; pH 6.7 to 7.1
Staphylococcus aureus ATCC 6538, CIP 4.83, NCTC 10788, NCIMB 9518,
Bacillus subtilis ATCC 6633, CIP 52.62, NCIMB 8054,NBRC 3134
Pseudomonas aeruginosa1 ATCC 9027, NCIMB 8626, CIP 82.118, NBRC 13275
Clostridium sporogenes2 ATCC 19404, CIP 79.3, NCTC 532 or ATCC 11437,
Candida albicans ATCC 10231, IP 48.72, NCPF 3179, NBRC 1594
ATCC 16404, IP 1431.83, IMI 149007, NBRC 9455
An alternative microorganism is Kocuria rhizophila (Micrococcus luteus) ATCC 9341.
An alternative to Clostridium sporogenes, when a nonspore-forming microorganism
is desired, is Bacteroides vulgatus (ATCC 8482).
Table: Strains of the Test Microorganisms Suitable for Use in the
Growth Promotion Test and the Method Suitability Test
Growth Promotion Test and Method Validation
USP <71> Sterility Test contains two qualifying Assays which must be
performed prior to sterility testing. They are “ Growth Promotion Test” and
“Validation Test” ( Bacteriostasis and Fungistasis Test)
Growth Promotion Test:
Test each lot of medium prior to use for sterility testing to ensure that the
medium used support the growth of <100 viable micro-organisms.
Inoculate portions of the media with less than 100 cfu of appropriate organisms.
Inoculate FTM with less than 100 cfu of Pseudomonas aeruginosa,
Staphylococcus aureus and Clostridium sporogenes . Inoculate SCDB
with less than 100 cfu of Bacillus subtilis, Candida albicans and less than 100
spores of Aspergillus brasiliensis. Incubate for not more than 3 days in case of
bacteria and not more than 5 days in the case of fungi.
The media are suitable if a clearly visible growth of the microorganisms occurs.
Method Validation / Suitability Test /Bacteriostatic and
• The Validation Test is used to determine if the test sample will
inhibit the growth of microorganisms in the test media.
• The Validation Test must be performed on each product prior
and / or during sterility testing.
• Microbiological growth in the presence of the test samples is
compared to controls without test samples. If microbial
growth is present in the sample and control, then the test is
• The microorganisms used for suitability test are same as
Growth Promotion Test.
1. Membrane Filtration
2. Direct Inoculation
After transferring the content of the container or containers to be tested to the
membrane, add an inoculum of a small number of viable microorganisms (not more
than 100 cfu) to the final portion of sterile diluent used to rinse the filter.
After transferring the contents of the container or containers to be tested (for catgut and
other surgical sutures for veterinary use: strands) to the culture medium, add an
inoculum of a small number of viable microorganisms (not more than 100 cfu) to the
In both cases use the same microorganisms as those described above under Growth
Promotion Test of Aerobes, Anaerobes, and Fungi. Perform a growth promotion test as a
positive control. Incubate all the containers containing medium for not more than 5
Quantity per Container
Minimum Quantity to be Used
(unless otherwise justified and authorized)
Less than 1 mL The whole contents of each container
1–40 mL Half the contents of each container, but not less than 1 mL
Greater than 40 mL, and not greater than 100 mL 20 mL
Greater than 100 mL 10% of the contents of the container, but not less than 20 mL
Antibiotic liquids 1 mL
Insoluble preparations, creams, and ointments to be suspended
Use the contents of each container to provide not less than 200 mg
Less than 50 mg The whole contents of each container
50 mg or more, but less than 300 mg Half the contents of each container, but not less than 50 mg
300 mg–5 g 150 mg
Greater than 5 g
Catgut and other surgical sutures for veterinary use 3 sections of a strand (each 30-cm long)
Surgical dressing/cotton/gauze (in packages) 100 mg per package
Sutures and other individually packaged single-use material The whole device
Other medical devices The whole device, cut into pieces or disassembled
Table : Minimum Quantity to be Used for Each Medium
Number of Items in the Batch*
Minimum Number of Items to be Tested for Each
Medium (unless otherwise justified and authorized) **
Not more than 100 containers 10% or 4 containers, whichever is the greater
More than 100 but not more than 500 containers 10 containers
More than 500 containers 2% or 20 containers, whichever is less
For large-volume parenterals 2% or 10 containers, whichever is less
Pharmacy bulk packages (<5 g) 20 containers
Pharmacy bulk packages ( 5 g) 6 containers
Bulks and blends See Bulk solid products
Ophthalmic and other noninjectable preparations
Not more than 200 containers 5% or 2 containers, whichever is the greater
More than 200 containers 10 containers
If the product is presented in the form of single-dose containers,
apply the scheme shown above for preparations for parenteral
Catgut and other surgical sutures for veterinary use 2% or 5 packages, whichever is the greater,
up to a maximum total of 20 packages
Not more than 100 articles 10% or 4 articles, whichever is greater
More than 100, but not more than 500 articles 10 articles
More than 500 articles 2% or 20 articles, whichever is less
Bulk solid products
Up to 4 containers Each container
More than 4 containers, but not more than 50 containers 20% or 4 containers, whichever is greater
More than 50 containers 2% or 10 containers, whichever is greater
* If the batch size is unknown, use the maximum number of items prescribed.
** If the contents of one container are enough to inoculate the two media, this column gives the number of containers
needed for both the media together.
Table : Minimum Number of Articles to be Tested in Relation to the Number of Articles in the Batch
Things to know Regarding Membrane Filtration
►This test is method of choice for pharmaceutical products.
►Use membrane filters having a nominal pore size not greater than 0.45 µm, in
which the effectiveness to retain microorganisms has been established.
►Cellulose nitrate filters are used for aqueous, oily, and weakly alcoholic
►Cellulose acetate filters are used for strongly alcoholic solutions.
Specially adapted filters may be needed for certain products (e.g., for antibiotics).
►Do not exceed a washing cycle of five times 100 mL per filter.
Use the same volume of each medium as in the Method Suitability Test.
►If the product has antimicrobial properties, wash the membrane not less than
three times by filtering through it each time the volume of the chosen sterile
diluent used in the Method Suitability Test.
►Transfer the whole membrane to the culture medium or cut it aseptically into
two equal parts, and transfer one half to each of two suitable media.
Things to know Regarding Direct Inoculation
►This test is method of choice for medical devices because the device is in direct
contact with media through out the incubation period.
►Transfer the quantity of the preparation to be examined directly into the culture
medium so that the volume of the product is not more than 10% of the volume of the
medium, unless otherwise prescribed.
►If the product to be examined has antimicrobial activity, carry out the test after
neutralizing with a suitable neutralizing agent or by dilution in a sufficient quantity of
►For extremely large devices, immerse those portions of the device that come in
contact with the patient in a volume of medium sufficient to achieve complete
immersion of those portions.
►Articles can be immersed intact or disassembled.
OBSERVATION AND INTERPRETATION OF RESULTS
• Technician must be trained as to how to detect growth during the incubation
• At intervals during the incubation period and at its conclusion, examine the
media for macroscopic evidence of microbial growth.
• After 14 incubation if the presence or absence of microbial growth can not
be determined because of the product nature which cause turbidity in the
media transfer portions (each not less than 1 mL) of the medium to fresh
vessels of the same medium, and then incubate the original and transfer
vessels for not less than 4 days.
• If no evidence of microbial growth is found, the product to be examined
complies with the test for sterility.
• If evidence of microbial growth is found, OOS should be conducted. This
investigation should include: Clean Room environmental test data, media
sterilization records, technician training record, the relative difficulty of the
test procedure, media controls data, personal monitoring data, bioburden
OBSERVATION AND INTERPRETATION OF RESULTS – CON’T
The test may be considered invalid only if one or more of the following conditions are
Error in test procedure used for the test.
Microbial growth is found in the negative controls.
After determination of the identity of the microorganisms isolated from the test,
the growth of this species (or these species) may be misunderstanding to faults
with respect to the material and or the technique used in conducting the sterility
• If the test is declared to be invalid, it is repeated with the same number of units as
in the original test.
• If no evidence of microbial growth is found in the repeat test, the product
examined complies with the test for sterility.
• If microbial growth is found in the repeat test, the product examined does not
comply with the test for sterility.
The four pillars of Sterility testing
•Personnel training & monitoring
If people are a major source
of contamination how do we
avoid contaminating the
product while testing?
Aseptic technique of wearing gloves
How often should gloves be examined and sanitized?
1 Sterile instruments should be held under Class 100 conditions between
uses and placed in sterile containers.
2 Operators should not contact sterile products, containers, closures, or critical
surfaces with any part of their gown or glove
3 Keep the entire body out of the path of unidirectional airflow
4 Contact sterile materials only with sterile instruments
Which is correct aseptic technique?
Which is correct aseptic technique?