Method Applicability in Microbiology

If there is one subject that the ANSM raises at every meeting/inspections report, this is the one!

But when they say : “Method applicability has not been validated in n% of the inspections and as a result each company has been rejected”, have we all fully understood what they are talking about?

In the event of such uncertainty, COSMEBAC has decided to clarify the subject for you.

So, what is “Method Applicability”?

In cosmetics, microbiological testing essentially complies with “standardised” protocols (mostly ISO). The idea, which should be understandable for everyone (and we mean everyone), is to have a set of “tools” or standard tests such that we can operate on the basis of results which will be both homogeneous and predictive.

Well, that’s the theory…

In practice, using and applying standardised protocols does not mean we do not have to validate their applicability. In other words, being able to answer the question “Is the count or detection that I observe a reflection of reality for this specific formula?” If there is any uncertainty (there’s that word again) it must be resolved.

“But… why?”

Every standard defines the idea of the method’s applicability. And this is even more so for cosmetics:

we have to deal with a very wide range of very distinct product forms: a loose powder is not subject to the same technical constraints as mascara or shower gel.

we know that a “negative” result may be a precise reflection of the reality (specific formula) but it may also be the masking effect of pollution from the residual inhibitive power of the preservative system, if this is not neutralised by the neutralising-diluent used.

we are heading towards a widespread use of unlisted anti-microbial molecules. This microbial stress “strategy”, often passed off as an in fine microbicide, can turn out to be only temporary in some cases. The bacterial flora thus persists in the product before continuing to proliferate.

– we use alternative detection methods. Flow cytometry or ATPmetry have been available in our microbiology laboratories for decades. Whilst their value is beyond any discussion they must however be validated in relation to the official “reference” methods.

“And what should we do about it?”

: nothing could be simpler; the standards themselves define the operational framework.

To put it simply, a comparison is made between two preparations with a known quantity of micro-organisms, one of the preparations contains the cosmetic formula to be tested and the other does not. The method will only be applicable if the quantities of micro-organisms are enumerated or detected in a similar way regardless of the presence of the cosmetic formula.

Simple, yes but not simplistic…

The operative methods can, of course, become more complex, strategic and technical choices may have to be made:

  • – Which neutralising diluent should be used?
  • – Which dilution factors should be tested?
  • – Which formulae could be reasonably grouped together to cover method applicability for all of the formulae concerned?

Dealing with such a large number of elements requires expertise and time if you want to avoid technical or financial errors.

COSMEBAC is always here to help you.

Contacts : Jean-Louis FIACRE et Simon CATROUX
Tél. : +33 2 40 68 50 50 –

Cosmepar Clinique
2 rue Voltaire
44 000 Nantes
………………………………… Laboratoires Cosmebac Analytec
2 rue Alessandro Volta
44270 Carquefou