How to use Dehydrated Culture Media
Quality control of culture media
As with all our products for microbiological applications, dehydrated culture media undergo stringent quality controls from the raw materials to the finished product. With these controls we wish to ensure, that in spite of the variations which always occur with natural substances (as we discussed in the previous section), we can provide the user with dehydrated culture media of high, and as far as possible, constant quality. In the descriptions of the individual culture media the strains which our laboratories used for testing in quality control and their reactions are listed. These define the microbiological properties of the individual culture medium concerned.
Many culture media are furthermore tested quantitatively by colony counts of bacteria or yeast cultures. These media are inoculated by the spiral plater method with cell suspensions of approximately 104 Cfu/ml.
After incubation and colony count the recovery rate related to a reference medium (e.g. Tryptic Soy Agar) is given as a percentage number.
In case of non-selective culture media numbers of nearly 100 % are expected and for a single result 70 % has been fixed as lower limit with respect to accuracy of the method.
The recovery rates on selective media are naturally lower even for the target organisms. Bacteria that should be suppressed on purpose are massively inoculated in order to recognize the inhibitor effect by means of a rather low recovery rate.