MacCONKEY SORBITOL AGAR BASE

MacConkey Sorbitol Agar is recommended by ISO Committee with a slight modification of MacConkey Sorbitol Agar formulated by Rappaport and Henigh. This medium is recommended for isolation of enteropathogenic Escherichia coli O157: H7, which ferments lactose but does not ferment sorbitol, hence produces colourless colonies. This organism has been recognized as a cause of hemorrhagic colitis. E. coli O157: H7 is a human pathogen associated with hemorrhagic colitis that results from the action of a shiga-like toxin. MacConkey Sorbitol Agar however should not be solely used to detect pathogenic E. coli O157: H7 strains as some non-toxic strains will also not ferment sorbitol.
On standard MacConkey Agar containing lactose, this strain is indistinguishable from other lactose-fermenting E. coli. In MacConkey Sorbitol Agar Base, lactose is replaced by sorbitol. Unlike most E. coli strains, E. coli O157:H7 ferments sorbitol slowly or not at all. The growth of E. coli O157:H7 on MacConkey Agar with Sorbitol shows colourless colonies and most of the fecal flora ferment sorbitol and appear pink. MacConkey Agar with Sorbitol therefore permits ready recognition of E. coli O157:H7.

a selective medium for isolation and detection of Escherichia coli O157:H7 from food and animal feedstu?