Use of Acclimatized Microorganisms in Validation Studies

For conventional culture based microbial methods and with many rapid and alternative microbiological methods, the way that method suitability is demonstrated is with the recovery of known populations of microorganisms. For years these were recognized cultures drawn from an approved culture collection. This test panel has generally become broadened to include environmental isolates, although this inclusion is not universally accepted and there remain some debate as to what this entails.

As an expansion upon this, some microbiologists, and also some regulators, have put forward the view that at least some of the microorganisms used for method verification should be ‘acclimatized’; that is closer to the state that they are in the environment from which a test sample is drawn. Acclimatized may also be stressed or even where the organism is damaged.

The reason for considering the inclusion of such ‘stressed’ organisms in studies is because organisms that have gone through a stress response maybe more difficult to recover (and, as an aside, harder to remove, inactivate or kill -to adapt an old aphorism: “what does not kill them makes them stronger”).

An example is with testing samples of water. In this context, the argument runs, challenge organisms should not be laboratory cultures grown on nutritious agar, but organisms held, for a period of time, in water (which will be a low nutrient environment and one subject to osmotic forces). This step will add robustness to method qualification and show that organisms can be recovered from given environmental niches.

This paper looks at how acclimatization might be achieved, in the context of method verification. The paper begins by looking at the objectives of method verification and then considers the appropriateness of environmental isolates in expanding microbial test panels. The paper then considers the how it can be ensured that environmental isolates are not simply facsimiles of laboratory cultures but are instead rendered to a closer approximation of the organism in its natural state in the environment.

The reference is:

Sandle, T. (2019) Use of Acclimatized Microorganisms in Validation Studies, Journal of Validation Technology, 25 (3): http://www.ivtnetwork.com/article/use-acclimatized-microorganisms-validation-studies

Posted by Dr. Tim Sandle, Pharmaceutical Microbiology