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:
Posted by Dr. Tim Sandle, Pharmaceutical Microbiology
No comments:
Post a comment
Pharmaceutical Microbiology Resources