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

The medium was developed by Curtis et al. (1989a) for the isolation of Listeria monocytogenes from faeces and other clinical samples and has also been recommended for the isolation of Listeria spp. from foods (Warburton et al., 1991a, 1991b; Anon., 1995). It utilises (i) the selective inhibitory components lithium chloride (Ludlam, 1949), acriflavine, colistin, fosfomycin, cefotetan and cycloheximide and (ii) the indicator system aesculin and ferric iron for the isolation and differentiation of listeria. Listeria spp. hydrolyse aesculin, producing black zones around the colonies due to the formation of black iron phenolic compounds derived from the aglucon. Gram-negative bacteria are completely inhibited. Most unwanted Gram-positive species are suppressed, but some coagulase-negative staphylococci may appear as aesculin-negative colonies. Some strains of enterococci grow poorly and exhibit a weak aesculin reaction, usually only after 40 h incubation. Typical Listeria monocytogenes colonies are usually visible after 24 h, but incubation should be continued for a further 24 h to detect slow-growing strains.