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X-α-Gal-based medium for simultaneous enumeration of bifidobacteria and lactic acid bacteria in milk

1991; Elsevier BV; Volume: 13; Issue: 1 Linguagem: Inglês

10.1016/0167-7012(91)90034-n

1872-8359

Pierre Chevalier, Denis Roy, L. Savoie,

Probiotics and Fermented Foods

A new method using the chromogenic substrate 5-bromo-4-chloro-3-indolyl-α-d-galactoside was developed for the differential enumeration of Bifidobacterium spp. and lactic acid bacteria used in preparation of fermented and nonfermented dairy products. The methodology is based on the high α-galactosidase activity of bifidobacteria as compared to that of Lactobacillus or Streptococcus strains. The X-α-Gal-based medium is useful to identify bifidobacteria among Lactobacillus since the enzyme action of α-galactosidase splits X-α-Gal substrate and releases indol which imparts a blue colour to bifidobacterial colonies on agar plates. The blue colonies can also be assigned to the genus Bifidobacterium using a simple permeabilization procedure with Triton X-100 which allows the reliable determination of fructose-6-phosphate phosphoketolase activity.