General concepts and principles guiding the use of reference materials is discussed in the section on chemical testing

The analysts rely on the performance of equipment, the reagents and his/her own performance on a long-term basis in generating reliable test results. However, all these parameters could show variations in their performance over short intervals and continuous discrete variation with time. It is important to eliminate effects arising from such variations on the test results. Use of reference materials gives an opportunity to compare the test results on a daily basis, or even at more frequent intervals, and decide on the acceptability of results. A laboratory may prepare their own reference materials to achieve the anticipated level of homogeneity of the test results. The results from this activity, however, carry limitations arising from the competence of the laboratory in preparing their own reference materials. It is even more difficult in case of microbiology where the main reference materials tend to be microbial cultures, which first needs to be checked against internationally accepted standard microbial cultures performing a wide variety of tests based on biochemical, serological and molecular biological methods.

Source of bacterial reference cultures:

American Type Culture Collectionhttp://www.atcc.org/

Address:

These cultures are used for two purposes. First, they are used to assess the quality of microbiological media prior to use. For this purpose, certain cultures that grow well in the media (positive) and those do not (negative) are used. This provides a mechanism to assess the selectivity of a given microbiological medium in isolation and identification of the microorganism separated from the matrices under tests. The catalogues of microbiological media suppliers indicate the ATCC cultures they use to establish the characteristics of the media. Secondly, the cultures are used to generate the color reactions which are considered typical. These are then visually compared with the color reactions shown by the test microorganisms. If they correspond this will confirm the test results generated using the microbiological media.