Alizarin-beta-D-galactoside: a new substrate for the detection of bacterial beta-galactosidase

We describe the synthesis of a new substrate for the detection of bacterial beta-galactosidase. This substrate, alizarin-beta-d-galactoside, is readil y hydrolysed to release alizarin which complexes with various metal ions to form brightly coloured chelates. A total of 367 strains of Gram-negative b acteria were examined for their ability to hydrolyse three chromogenic subs trates: alizarin-beta-d-galactoside (Aliz-gal), cyclohexenoesculetin-beta-d -galactoside (CHE-gal) and 5-bromo-4-chloro-3-indolyl-beta-d-galactoside (X -gal). A total of 182 strains (49.6%) were found to hydrolyse at least one of the three substrates. All of these 182 strains (100%) hydrolysed Aliz-ga l whereas only 170 (93.4%) and 173 (95.1%) hydrolysed CHE-gal and X-gal, re spectively. We conclude that alizarin-beta-d-galactoside is a highly sensit ive substrate for the demonstration of beta-galactosidase.