MacConkey Sorbitol Agar with Cefixime and Tellurite

Selectively detect sorbitol-negative Escherichia coli O157:H7 (VTEC) with Thermo Scientific™ Remel™ MacConkey Sorbitol Agar with Cefixime and Tellurite. The medium is recommended by Food and Drug Administration Center for Food Safety and Applied Nutrition (FDA/CFSAN) and the American Public Health Association (APHA) for selective isolation of VTEC from food samples^6,7.

Verotoxin-producing Escherichia coli (VTEC), which includes serotype O157, is the fourth leading cause of diarrheal diseases in the United States⁴. This serotype of E. coli produces a verotoxin and is indistinguishable on the routine isolation media from those of non-VTEC E.coli. E. coli O157 is recognized as a cause of haemorrhagic colitis, an illness characterized by bloody diarrhoea and severe abdominal pain, and haemolytic uraemic syndrome (HUS)⁵ and as such, is a significant human pathogen.

Selectively detect sorbitol-negative Escherichia coli O157:H7 (VTEC) with MacConkey Sorbitol Agar with Cefixime and Tellurite.

• Ease of differentiation: Due to the presence of D-sorbitol; sorbitol negative strains form colorless colonies while other E. coli strains that ferment sorbitol and form pink colonies.
• Selective: Bile salts and crystal violet are selective agents which inhibit gram-positive organisms and enterococci, respectively. Cefixime and tellurite inhibit the growth of non-verotoxin producing E.coli and other non-sorbitol fermenting bacteria.
• Recommended as a simple, inexpensive, rapid and reliable means of screening for E. coli O157
• Recommended by FDA, Center for Food Safety and Applied Nutrition (FDA/CFSAN) and theAPHA for selective isolation of VTEC from food samples^6,7.

In 1986, March and Ratnam introduced MacConkey Agar with sorbitol for the isolation of this serotype as unlike other serotypes VTEC does not ferment sorbitol¹. In 1991, Chapman modified this medium by adding cefixime to specifically inhibit Proteus spp². Zadik further modified it by adding potassium tellurite and found that it more effectively inhibited the growth of non-VTEC strains and increased isolation of E. coli O157³.

This medium contains peptones that provides nitrogenous compounds and amino acids essential for bacterial growth. Bile salts and crystal violet are selective agents which inhibit gram-positive organisms. Cefixime and tellurite inhibit the growth of non-verotoxin producing E.coli and other non-sorbitol fermenting bacteria. Lactose is substituted with D-sorbitol. Verotoxin- producing strains of E.coli ferment lactose but not sorbitol and form colorless colonies.

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