Most of the biochemical characterization tests described in this Manual should be controlled by organisms that are known to give either positive or negative reactions under appropriate conditions. For this purpose, we list in Table Dl the species recommended together with the accession numbers of suitable strains available from the National Collection of Type Cultures, Central Public Health Laboratory, Colindale Avenue, London NW9 5HT and, in many instances, also from the American Type Culture Collection, 12301 Parklawn Drive, Rockville, Maryland 20852, USA. As controls for the common tests shown in Table D2, the set of four strains given is adequate. For other bacterial characters, the test strains shown in Table D3 may be used. We emphasize, however, that most of the organisms shown in these tables are pathogenic so that due regard must be paid to safety and hygiene in the laboratory.

For the maintenance and storage of test-control strains, freeze-dried (lyophilized) cultures which retain their characters and keep virtually indefinitely are ideal. However, for those who wish to keep frequently used strains for immediate use, we give in Table D4 suggestions for the nutrient media, cultural conditions and short-term storage period in order to be reasonably sure of their survival before they need replacement from stock cultures.