Evaluation of a novel modified selective medium cefixime-tellurite-phosphate-xylose-rhamnose MacConkey agar for the isolation of Escherichia albertii from diarrheal stool specimens

Abstract

It is challenging to isolate Escherichia albertii from clinical specimens. Therefore, a medium that can selectively grow E. albertii and differentiate it from E. coli is earnestly desired. Here, we describe the evaluation of a recently developed selective differential medium, called cefixime-tellurite-phosphate-xylose-rhamnose-MacConkey (CT-PS-XR-MacConkey) medium, which enables the specific growth of E. albertii and differentiation of E. albertii (colorless) from E. coli (red) based on colony color and thus, facilitating the efficient isolation of E. albertii from diarrheal stool. When three E. albertii negative diarrheal stools were inoculated onto CT-PS-XR-MacConkey and xylose-rhamnose-melibiose (XRM) containing MacConkey agars, no colorless colonies were observed on both the media. However, when E. albertii was spiked into these three diarrheal stools, the ratio of colorless colonies to red colonies was higher on CT-PS-XR-MacConkey agar compared to XRM-MacConkey agar in all three samples. Notably, out of 105 Eacdt-gene PCR negative diarrheal stools 56 yielded colorless colonies on MacConkey agar while out of these 56 diarrheal stools, nine yielded colorless colonies on XRM-MacConkey but no colorless colonies were observed on CT-PS-XR-MacConkey agar. Furthermore, evaluation of these two media with five E. albertii positive-stool specimens revealed that the number of red colonies were constantly less, whereas that of colorless colonies were constantly more on CT-PS-XR-MacConkey agar, thus aiding in efficient isolation. Altogether, these results suggest that the CT-PS-XR-MacConkey agar could be a useful selective differential medium for isolation of E. albertii from diarrheal stool specimens.