A bacteriologist often uses a slanted agar medium containing lactose, sucrose, and glucose, along with ferrous sulfate and phenol red, to differentiate bacteria based on carbohydrate fermentation patterns and hydrogen sulfide production. The medium’s appearance after bacterial incubation provides valuable diagnostic clues, indicated by changes in color and the formation of gas. For instance, a yellow slant and butt signify glucose fermentation, while a yellow butt with a red slant suggests only glucose utilization. Cracks or lifting of the agar indicate gas production, and blackening signifies hydrogen sulfide production.
This differential medium offers a rapid and cost-effective method for presumptive bacterial identification. Its ability to distinguish fermentation patterns and detect hydrogen sulfide production aids in classifying various bacterial genera, particularly Enterobacteriaceae. Developed over a century ago, this technique remains a cornerstone of microbiological analysis in clinical, food safety, and environmental laboratories, contributing significantly to the identification of microbial pathogens and contaminants.
