This monograph has been assessed by members of the IUMS–ICFMH Working Party on Culture Media and given ‘Approved’ status.

This medium was devised for the detection of carnobacteria (syn. Lactobacillus divergens) which fail to grow well on conventional selective media for lactobacilli (Holzapfel and Gerber, 1983). Investigations showed pH values below 6.0 to be inhibitory to carnobacteria, especially in the presence of acetate. Growth of carnobacteria was found to take place at pH values of up to 11.0 (Holzapfel and Long, unpublished results), compared to a maximum pH of 7.2 for growth of practically all lactobacilli. Also, relatively high concentrations of between 0.4 and 1% manganese sulfate have been found to stimulate growth of carnobacteria more than that of enterococci (Bosch and Holzapfel, unpublished results). In order to minimise Maillard reactions during heat sterilisation of such alkaline media, glucose was substituted by sucrose. Thus far, all carnobacteria have been found to ferment sucrose. The selectivity of the CTAS medium is based on its high pH (8.5–9.0) and the presence of thallium acetate, nalidixic acid and a relatively high concentration of sodium citrate.