What is macconkey agar with sorbitol?

MacConkey agar with sorbitol is a selective and differential culture medium used to aid in the isolation and identification of the gram-negative bacterium called Escherichia coli 0157:H7.

This medium contains a pH indicator, crystal violet, bile salts, lactose, and sorbitol. Lactose is a fermentable sugar, while sorbitol is a non-fermentable sugar. The presence of lactose in the medium allows for the selective growth of gram-negative bacteria, while crystal violet and bile salts inhibit the growth of gram-positive bacteria.

The addition of sorbitol makes it possible to differentiate between E. coli O157:H7 and other non-pathogenic types of E. coli, as the strain produces a distinct non-sorbitol-fermenting phenotype. This means that E. coli O157:H7 will not produce acid from sorbitol fermentation and will appear as colorless colonies, while other strains of E. coli will appear pink-red colonies.

MacConkey agar with sorbitol is commonly used in clinical laboratories to diagnose and confirm the presence of E. coli O157:H7 in stool samples of patients with diarrhea. Prompt identification of this pathogen is important as it can cause severe gastrointestinal illness and potentially fatal complications.