Detection of Bifidobacteria by α - galactosidase activity

This method using the synthesis substrate of 5-bromo-4-chloro-3-indolyl-α-galactoside (X-α-Gal) was examined for the differential enumeration of Bifidobacteria and lactic acid-producing bacteria. Bifidobacteria possess a high level of α-galactosidase activity. Biffdobacterium longum KCTC 3215 exhibited the highest α-galactosidase specific activity (8.57 units/㎎ protein). Determination of α-galactosidase activity using the PNPG procedure showed that Lactobacillus, Streptococcus, Pediococcus, and Leuconostoc strain had lower α-galactosidase activity as compared to Bifidobacteria. The X-α-Gal based medium is useful to identify Bifidobacteria among lactic acid-producing bacteria since the enzyme action of α-glactosidase spilts X-α-Gal substrate and releases indol which impacts a blue color to Bifidobacterial colonies on agar plates. All strains of Bifidobacteria appeared as blue colonies on MRS agar medium supplemented with 100 μM X-α-Gal while colonies of other lactic acid-producing bacteria appeared white or light blue.