Sugar Fermentation Test in Clinical Microbiology Laboratory

Sugar Fermentation Test is a biochemical test used to determine the ability of bacteria to ferment specific carbohydrates (such as glucose, lactose, sucrose, mannitol, etc.) and produce acid with or without gas. It helps in the identification and differentiation of bacterial species based on their carbohydrate utilization pattern. Principle: Bacteria are inoculated into a broth containing a specific sugar, a pH indicator (e.g., Andrade indicator or phenol red), and a Durham tube for gas detection. Fermentation of the sugar produces acid, causing a color change in the medium. Gas production, if present, is collected in the Durham tube. Interpretation: Acid production (A): Color change indicating fermentation of the sugar. Acid and Gas production (AG): Color change with a gas bubble in the Durham tube. No fermentation (-): No color change and no gas production. Clinical Importance: The test helps differentiate members of the family Enterobacteriaceae and other Gram-negative bacilli. It is useful in identifying organisms such as: Escherichia coli Klebsiella pneumoniae Salmonella Typhi Shigella dysenteriae