HiCrome^™ MacConkey-Sorbitol Agar

Application

HiCrome^™ MacConkey Sorbitol Agar is recommended for selective isolation of Escherichia coli 0157:H7 from food and animal feeding stuffs. MacConkey Sorbitol Agar is based on the formulation described by Rappaport and Henigh. The medium contains sorbitol instead of lactose and it is recommended for the detection of enteropathogenic strains of E. coli 0157:H7 which ferments lactose but does not ferment sorbitol and hence produce colorless colonies. Sorbitol fermenting strains of E. coli produce pink-red colonies. The red color is due to production of acid from sorbitol, absorption of neutral red and a subsequent color change of the dye when pH of the medium falls below 6.8. E. coli 0157:H7 has been recognised as a cause of haemorrhagic colitis. B.C. indicator is added to detect the presence of an enzyme β-D-glucuronidase which is specific for E. coli. Stranins of E. coli possessing β-D-glucuronidase appear as blue colored colonies on the medium. Enteropathogenic strains of E. coli 0157 do not possess beta-D-glucuronidase activity and thus produce colorless colonies. E. coli fermenting sorbitol and possessing beta-D-glucuronidase activity produce purple colored colonies. Most of the gram-positive organisms are inhibited by crystal violet and bile salts. Addition of Tellurite-Cefixime Supplement makes the medium selective. Potassium Tellurite selects the serogroups 0157 from other E. coli serogroups and inhibits Aeromonas species and Providencia species. Cefixime inhibits Proteus species.

Reconstitution

Suspend 50.1 g in 1 liter of distilled water. Boil gently to dissolve the medium completely. DO NOT AUTOCLAVE. Cool to 50 °C. Mix well and pour into sterile petri plates. If desired add Tellurite-Cefixime Supplement to the molten and cooled medium (50 °C) before pouring into sterile petri plates.

Legal Information

HiCrome is a trademark of HiMedia Laboratories Pvt. Ltd.