New microbiological methods for sterile compounding: Are there applications to hospital pharmacies?
The traditional methods used for detecting or counting micro-organisms require growth of the micro-organisms in a culture medium, followed by observation of clouding of the medium (detection in a liquid medium) or the formation of colonies (detention or counting in a solid agar medium), each colony corresponding to an initial micro-organism prior to growth. The necessity of having this growth phase has 2 major disadvantages: the time factor (it takes between 3 and 14 days to visualise detection for everyday micro-organisms) and the ease with which the micro-organism can be cultivated in the culture medium used.
Alternative methods in microbiology are therefore expected to provide a reduction in the time to result and if possible a direct determination of the micro-organism and a simplification of the methodology. Two large groups of method can be highlighted and will be presented: the direct methods enabling detection of the micro-organism as an individual, living cell, and the methods which require microbial growth but with means of detection which are faster than microbial clouding or the formation of colonies visible to the naked eye.
Unfortunately, there is currently no alternative method to traditional methods which is applicable to all microbiological analyses and to all products. Sufficiently precise specifications should enable a choice between all the methods available. Two examples applicable to hospital pharmacy – sterility of mixes of parenteral preparations with and without lipids, and surface monitoring of the efficacy of cleaning/disinfection – will be presented with the alternative methods than can be employed.
As with traditional methods, performance qualification (PQ) of the method is necessary, that can be broken down into different phases: PQ1, verification of the expected performance of the method with standard test micro-organisms and without product; PQ2, performance of the method applied to the products with a comparison with the traditional method.
The objective of these validations is to demonstrate that the method makes it possible to detect such micro-organisms as may be present in the product analysed in a reproducible manner and at least as well as the traditional method.
With appropriate validation and above all if application of the traditional methods is difficult, the alternative methods in microbiology are accepted from the regulatory viewpoint.