Evaluation of a chromogenic agar medium for isolation of Escherichia coli O26

Abstract

CT-O26 medium, a chromogenic agar medium which has been recently developed for selective isolation of Escherichia coli O26, was evaluated isolating E. coli O26 from 25 g of food samples artificially contaminated with ca. 2 colony forming units of the organism. After food samples were cultured in modified E. coli broth with novobiocin at 42 °C for 18 h, the culture was streakily plated onto CT-O26 medium and rhamnose MacConkey agar medium with cefixime and tellurite (CT-RMAC) which has been reported as an effective medium for isolation of E. coli O26. CT-O26 medium was more effective than CT-RMAC for isolating E. coli O26 from ground beef, liver and alfalfa sprouts samples. E. coli O26 was isolated from all ground beef and liver samples in combination with plating onto O26 medium and immunomagnetic separation (IMS) method.