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

The history of this medium is summarised by Mossel et al. (1978). It utilises (i) the selective inhibitory components azide and kanamycin and (ii) the indicator system aesculin and ferric iron for the isolation and differentiation of group D streptococci. Growth of the majority of unwanted organisms is suppressed, while sought organisms hydrolyse aesculin, producing black zones around the colonies due to the formation of black iron phenolic compounds derived from the aglucon. The selectivity of the medium can be increased by incubation at 42±0.5°C. The selective agents inhibit aesculin hydrolysis of species belonging to the Enterococcus avium and Enterococcus caecorum groups (Devriese et al., 1993). Aesculin-positive Lactobacillus strains should be excluded by confirmatory tests (Reuter, 1985). In water microbiology the medium is used as a confirmatory test for enterococci by the demonstration of aesculin hydrolysis (Anon., 2006).