ABC medium, a new chromogenic agar for selective isolation of Salmonella spp.

W e describe a new chromogenic agar medium, ABC medium (alpha beta-chromogenic medium), which includes two substrates, 3,4-cyclohexenoesculetin-beta-D-galactoside and 5-bromo-4-chloro-3-indolyl-alpha-D-galactopyranoside to facilitate the selective isolation of Salmonella sop. This medium exploits the fact that Salmonella spp, may be distinguished from other members of the family Enterobacteriaceae by the presence of alpha-galactosidase activity in the absence of beta-galactosidase activity. A total of 1,022 strains of Salmonella spp, and 300 other gramnegative strains were inoculated onto this medium. Of these, 1,019 (99.7%) strains of Salmonella spp, produced a characteristic green colony, whereas only 1 strain (0.33%) of non-Salmonella produced a green colony. A total of 283 stool samples were cultured onto desoxycholate citrate (DC) agar and ABC medium by direct inoculation and after selective enrichment in selenite broth. Overalll the sensitivity and specificity were superior for;ABC medium (100 and 90.5%, respectively) than for DC agar (88 and 26.9%, respectively). We conclude that ABC medium offers a high degree of specificity for the detection of Salmonella spp, in stool samples.