Biochemical characterization of anaerobic bacteria by an impregnated disk method

Simple disk technique for carbohydrate fermentation and esculin hydrolysis testing of anaerobic gram-negative bacilli

Carbohydrate fermentation by anaerobic gram-negative bacilli was easily detected using Taxo-Disks placed on supplemented Columbia Agar. After incubation, two drops of a 0.2% solution of bromothymol blue were added to each disk: yellow coloring was indicative of a positive reaction. In the esculin hydrolysis test paper disks impregnated with 2 mg of esculin were placed on the same medium. The results were read after addition of two drops of a 10% solution of ferric chloride. When testing slow-growing and/or serophilic anaerobic gram-negative bacilli, such as Bacteroides melaninogenicus or Bacteroides oralis, the supplemented Columbia Agar was enriched with 10% sterile horse serum. Discrepancies between results with the conventional tube technique and the disk method were occasionally observed with salicin only.