Bringing the sterility test into the 21st Century

8th June 2015

The Growth Direct System for sterility testing
A time line of cell growth

Anna Mills looks at a system that modernises sterility testing via automation and rapid results

Sterility testing has remained unchanged for many years within the pharmaceutical industry. Current testing relies on the filtration or direct inoculation of both Fluid Thioglycollate Medium (FTM) and Soya-Bean Casein Digest medium.

This method has been used by the European Pharmacopeia sector for many years and provides the user with the following challenges and risk factors:

* Turbidity. This is a subjective presence absence technique, which requires the user to make  a judgement on whether the solution incubated does indeed contain growth.

Turbid solutions. Any turbid solutions used need to have a further 4-7 days incubation added to declare them sterile, making the total incubation time 18-21 days rather than the general 14 days used. This extra step also adds the risk factor of a contamination event and therefore a potential false positive.

Manual handling. As with all manual tests there are potential opportunities for mistakes in incubation and/or contamination events, leading to the wrong result being reported.

Information handling. Traditional testing needs traditional results writing which can lead to transcription errors and unclear handwriting.

Time taken. The sterility result is the highest risk result and has a direct effect on patient health. It also therefore has the longest incubation time and can create a bottleneck in terms of drug supply. It can also mean that a sterility failure can potentially remain undetected within a manufacturing line for up to two weeks, providing more time for contamination to become widespread with more potential product waste.

New systems based on proven technologies have created a solution for sterility testing with advanced automation and detection methods. These systems align closely with traditional testing, making them easier to validate. The technologies also enable comparable results in half the time of the traditional test, a significant time saving.

An example of this technology is the Growth Direct system for sterility testing. It is designed to mirror the traditional sterility incubation regimen to cover the three existing conditions in the traditional sterility cassette, 2 aerobic and 1 anaerobic to provide testing at both 20-25°C and 30-35°C.

Like the traditional test, samples are filtered using on-market sterility pumps through a standard mixed ester membrane to capture the micro-organisms. Once captured, media is added and the samples loaded into the automated technology. Within the Growth Direct system, advanced robotics manage the incubation and colony detection process, reading samples every few hours and analysing the results to determine if there is growth.

Automated, non-destructive rapid methods such as this detect microcolonies of around 100 cells, rather than the 5x106 cells forming a colony that a human eye may see.

For this reason bacterial growth can be detected faster than a manual test and therefore a negative test can be recorded in around half the time of the traditional test, making the sterility test take 7 days rather than the traditional 14.

In addition, traditionally turbid samples are not an issue after filtration, meaning that the 18-21 days required using the traditional method is not required and the test will still only take 7 days. Initial detection of growing colonies can occur in the first few hours. This significant reduction in time to results can have a measurable impact in a manufacturer’s ability to ship high quality product more rapidly, or potentially respond faster to pandemics with vaccines.

Sterility testing is a time-consuming process that must be performed. Automated technologies such as the Growth Direct system can provide a solution that provides a comparable result in about half the time and reduces resource requirements, providing a faster non-destructive test with more traceable results. 

For more information at

Anna Mills is senior validation specialist at Rapid Micro Biosystems, USA.





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