Use of 5-Bromo-4-Chloro-3-lndoxyl-β-D-Glucuronide in MacConkey Sorbitol Agar to Aid in the Isolation of Escherichia coli 0157:H7 from Ground Beef

Abstract

The addition of 5-bromo-4-chloro-3-indoxyl-β-D-glucuronide (BCIG) at the 0.1 g/L level, to MacConkey sorbitol agar (MSA) plates aided in the isolation of Escherichia coli 0157:H7 from raw ground beef samples by differentiating β-glucuronidase positive from β-glucuronidase negative colonies. E. coli 0157:H7 colonies, being sorbitol negative, β-glucuronidase negative, remained white, while sorbitol negative, β-glucuronidase positive colonies turned green to blue. Addition of BCIG to the MSA agar reduced the number of false suspect colonies picked from the primary plating medium by 36% when compared to MSA. E. coli 0157:H7 was isolated from 11 out of 12 inoculated meat samples (0.7 E. coli 0157:H7/g) using MSA-BCIG as compared to 8 out of 12 samples using MSA without BCIG.