Cyanide media in the differentiation of enteric bacteria.

For more than 20 years the use of media containing potassium cyanide (KCN) has been advocated in the study of enteric bacteria. Braun and Guggenheim (1932) and Braun (1938, 1939) noted that cultures of the Klebsiella-Aerobacter group were able to grow in concentrations of KCN which inhibited Escherichia coli. Buttiaux (1952) employed the medium of Braun in the study of 280 Salmonella cultures and 56 cultures of the Bethesda (Bethesda-Ballerup) group (Edwards, West and Bruner, 1948; Bruner, Edwards and Hopson, 1949). The Bethesda-Ballerup group, as shown by West and Edwards (1954), is composed of cultures of Escherichia freundii which ferment lactose slowly or not at all and which, because of the similarity of biochemical reactions, long have been confused with salmonellae. Buttiaux found that the Bethesda cultures grew readily in Braun's medium whereas Salmonella were uniformly negative and the two groups could be distinguished with certainty within 24 hours. While the results obtained by Buttiaux represented a notable contribution to the differentiation of the bacteria, the medium of Braun was time consuming in its preparation and was extremely unstable. It remained for M0ller (1954) to devise a medium which could be prepared more simply and which was more stable, being usable for two weeks according to the statement of the author. The results of M0ller (1954) and of Kauffmann and M0ller (1955) indicated that this medium yielded reliable results in the differentiation of enteric bacteria. So far as the routine use of KCN medium in the diagnostic laboratory was concerned, M0ller's medium failed to fulfil only two requirements. The useful life of the medium was said to be only two weeks when stored at 4 C, and it contained ingredients not readily available in this country. The purposes of the present investigation were threefold: To test the action of M0ller's medium on larger numbers of cultures than had hitherto been examined, particularly cultures of the Salmonella, Bethesda and Arizona groups; to determine the length of time the medium could be stored and to find a more stable cyanide which could be substituted for KCN; and to substitute a readily available peptone for the Danish peptone employed by M0ller.