Development of XRM-MacConkey agar selective medium for the isolation of Escherichia albertii

Escherichia albertii has increasingly been recognized as an emerging pathogen. However, lack of selective medium for E. albertii is the bottleneck for clinical and epidemiological investigations. In this study, a selective medium for E. albertii named XRM-MacConkey agar, which is modified MacConkey agar supplemented with xylose (X), rhamnose (R), and melibiose (M) instead of lactose, was developed and evaluated. All 49 E. albertii and 6 different species out of 23 grew as colorless colonies, whereas 17 remaining species grew as red colonies. Detection limit of E. albertii by this medium was 10⁵ CFU/g stool when examined with spiked healthy human stool. Furthermore, colorless colonies on XRM-MacConkey agar obtained from 7 E. albertii-positive diarrheal stools were consistently E. albertii. In contrast, 57%, 18%, and 36% colorless colonies on MacConkey, DHL, and mEA agars, respectively, were non-E. albertii. We concluded that XRM-MacConkey agar could specifically be used for isolation of E. albertii.