Evaluation of novel chromogenic substrates for the detection of bacterial β ‐glucosidase

Aims:  To evaluate three previously unreported substrates for the detection of β ‐glucosidase activity in clinically relevant bacteria and to compare their performance with a range of known substrates in an agar medium. Methods and Results:  The performance of 11 chromogenic β ‐glucosidase substrates was compared using 109 Enterobacteriaceae strains, 40 enterococci and 20 strains of Listeria spp. Three previously unreported β ‐glucosides were tested including derivatives of alizarin, 3′,4′‐dihydroxyflavone and 3‐hydroxyflavone. These were compared with esculin and β ‐glucoside derivatives of 3,4‐cyclohexenoesculetin, 8‐hydroxyquinoline and five indoxylics. All substrates yielded coloured precipitates upon hydrolysis in agar. Alizarin‐ β ‐ d ‐glucoside was the most sensitive substrate tested and detected β ‐glucosidase activity in 72% of Enterobacteriaceae strains and all enterococci and Listeria spp. The two flavone derivatives showed poor sensitivity with Gram‐negative bacteria but excellent sensitivity with enterococci and Listeria spp. Conclusions:  Alizarin‐ β ‐ d ‐glucoside is a highly sensitive substrate for detection of bacterial β ‐glucosidase and compares favourably with existing substrates. β ‐glucosides of 3′,4′‐dihydroxyflavone and 3‐hydroxyflavone are effective substrates for the detection of β ‐glucosidase in enterococci and Listeria spp. Significance and Impact of the Study:  The data presented allow for informed decisions to be made regarding the optimal choice of β ‐glucosidase substrate for detection of pathogenic and/or indicator bacteria.