sterility testing

membrane filtration method

• filtration system and membrane are first sterilised

• design must allow process to be carried out under aseptic conditions

• after filtration, either:

  • transfer the whole membrane into the culture medium

  • cut the membrane aseptically into 2 equal parts and transfer each half to 2 suitable media

  • transfer the medium onto the membrane in the apparatus

• then, incubate the media for >14 days

direct inoculation method

• transfer qty of preparation directly into the culture medium, so that the product is not more than 10% of the vol of the medium

  • you don’t want to dilute the culture media → may no longer support growth of mo of interest

what are the 2 types of media?

• fluid thioglucollate medium (FTM)

• soya-bean casein digest medium (SCDM)

what is fluid thioglycollate medium suitable for the culture of?

• anaerobic and aerobic bacteria

what is soya-bean casein digest medium suitable for the culture of?

• aerobic bateria and fungi

what temp is FTM incubated at?

• 30-35 deg C

what temp is SCDM incubated at?

• 20-25 deg

what are the 3 control tests?

• sterility (negative control)

• growth promotion test (positive control)

• validation test (main positive control)

sterility test (negative control)

• is done to eliminate false positives and to ensure growth of mo is from products and not from the environment or culture itself that may be contaminated

• incubate portions of JUST the media on its own for 14 days

• no growth of mo is expected

• should be performed in parallel with the test for sterility of the product

growth promotion test (positive control)

• confirm media supports the growth of specifically chosen mo that are deliberately added in

• usually done prior to the test for sterility → no point doing the entire sterility test if the mo are unabble to grow in the media

validation test (main positive control)

• is done to confirm there is no growth-inhibitory effect in the product, e.g. preservative

• should be performed in parallel with the test for sterility of the product

• a small no. of viable mo is to be added to the contents of the product to be tested, and then incubated for not more than 5 days

  • if there is growth of mo → the product either possesses no antimicrobial activity, or such activity has been satisfactorilty eliminated

    • in this case, test for sterility may then be carried out w/o further modification

  • if there is no growth of mo → the product possesses antimicrobial activity that has not been satisfactorily eliminated under the conditionsof the test

    • conditions need to be changed in order to eliminate the antimicrobial activity, and validation test is to be repeated

the test may be considered invalid if…

• the data of the microbiological monitoring of the sterility testing shows a fault

• a review of the testing procedure used during the test reveals a fault

• microbial growth is found in the negative controls

• the identity of mo isolated from the test proves a fault with respect to the material and/or technique used in conducting the sterility test

what do you do if the test is declared to be invalid?

• if it is repeated w the same no of units as in the original test

what do you do if there is no evidence of microbial growth in the repeat test?

• the product examined complies w the test for sterility

what do you do if microbial growth is found in the repeat test?

• the product examined does NOT comply with the test for sterility