SORBITOL AGAR (MacCONKEY SORBITOL AGAR)

MacConkey Sorbitol Agar is based on the formulation described 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 (SLT). 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 colorless 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

for isolation and identi?cation of enteropathogenic E.coli strains associated with infant diarrhoea