Lab method
Triple sugar iron agar
Slant/butt fermentation + H2S blackening
High-yield clue
A black TSI butt signals H2S production, a classic Salmonella and Proteus study clue.
Overview
A differential medium with glucose, lactose, sucrose, and iron salts read as slant-over-butt color plus gas and hydrogen sulfide to profile enteric Gram-negative fermentation vocabulary.
Classification
- Differential medium concept
- Phenol red pH indicator
- Ferrous sulfate H2S indicator
Lab & identification clues
- Yellow slant/butt (A/A) = lactose or sucrose fermenter
- Red slant, yellow butt (K/A) = glucose-only fermenter
- Black precipitate = H2S positive
- Cracks/bubbles = gas production
Associations
- Salmonella and Proteus H2S vocabulary
- Lactose vs non-lactose fermenter framing
- Enteric Gram-negative profiling
Commonly confused with
- MacConkey agar
- EMB agar concept
Your notes
Original concept summary for coursework. Sources checked: OpenStax Microbiology 2e and NCBI Bookshelf Medical Microbiology; reviewed 2026-06. Describes vocabulary and interpretation concepts only; not a lab protocol and not for handling specimens or identifying patient isolates.