Description
Amyl Columbia CNA agar, when supplemented with horse or sheep blood is used for the selective and differential isolation of Staphylococcus sp., Streptocococcus sp, Enterococcus sp. and other gram positive bacteria from specimens containing mixtures of organisms. The basal medium combines the highly nutritious ingredients of Columbia agar, with the selective substances Colistin Sulphate (also known as Polymixin C) and Nalidixic Acid, both of which have low MICs for a wide spectrum of gram negative organisms, but have relatively high MICs for the majority of gram positive bacteria. The presence of horse or sheep blood in the medium provides an additional source of nutrients as well as haemolytic reactions by members of the Genus Streptococcus, which assist in their provisional identification.
The antimicrobials in the medium inhibit growth of many gram negative organisms, including members of the Genus Enterobacteriaceae, Colistin interfering with cell membrane formation and Nalidixic Acid affecting DNA replication.
