The Growth Promotion Test (GPT) for Soybean Casein Digest Agar (SCDA), also known as Tryptic Soy Agar (TSA)
Quality control procedure used in microbiological testing to verify the suitability of the media for supporting microbial growth.
The GPT ensures that SCDA can support the growth of microorganisms at the expected levels.
It verifies that the media is able to promote the growth of both specified and non-specified organisms, confirming the reliability of microbiological testing.
SCDA is a universal media that supports the growth of a wide range of organisms.
Specific microbial strains are used in the test, which are commonly required by pharmacopeial standards
𝐒𝐭𝐚𝐧𝐝𝐚𝐫𝐝 𝐎𝐫𝐠𝐚𝐧𝐢𝐬𝐦𝐬 𝐈𝐧𝐜𝐥𝐮𝐝𝐞𝐝
- Staphylococcus aureus (ATCC 6538) (18-24hrs) 30-35°C
- Pseudomonas aeruginosa (ATCC 9027)(18-24hrs) 30-35°C
- Bacillus subtilis (ATCC 6633)(18-24hrs) 30-35°C
- Candida albicans (ATCC 10231)(72-120hrs) 30-35°C
- Aspergillus brasiliensis (ATCC 16404) (72-120hrs) 30-35°C
𝐏𝐫𝐨𝐜𝐞𝐝𝐮𝐫𝐞
- Inoculate the test medium with a small number of microorganisms, typically not more than 100 colony-forming units (CFU).
- Pour 15–20 mL of the test agar medium into sterile Petri plates.
- Ensure that the temperature of the molten medium is below 45°C before inoculation.
- Prepare duplicate test plates and one negative control plate.
- Incubate the plates at the appropriate temperature for the specified incubation period.
- After incubation, compare the growth of the test microorganisms with that obtained on a control medium (such as a previously validated GPT batch or fresh medium)
- The medium passes the Growth Promotion Test if the test organisms grow as expected and produce the required number of colonies.
P1+P2/2
Where P1 and P2 are plate 1 and plate 2
Factor of 2 is standard inoculum size is multiplied by 2 and divided by 2
𝐄𝐱𝐚𝐦𝐩𝐥𝐞: 50 Standard inoculum
50×2= 100, 50/2=25
Acceptance criteria
25-100 cfu
A factor of 2 is commonly interpreted as a recovery of 50 to 200% As per PDA Colonies should be within 2 factor.
Recovery should be not less than 75%
%Recovery= how is number of cfu recovered/average number of cfu add×100