What role does sodium thiosulfate play in triple sugar iron agar?

Sodium thiosulfate plays a critical role in triple sugar iron agar as it serves as an indicator for hydrogen sulfide production. When certain bacteria metabolize the sodium thiosulfate, they produce hydrogen sulfide gas (H2S). This gas reacts with iron salts in the medium, resulting in the formation of a black precipitate of iron sulfide, which indicates H2S production. This characteristic is vital for differentiating among various types of enteric bacteria based on their metabolic capabilities.

The other components of the medium, such as sugars, provide a source of fermentation substrates, while sodium thiosulfate specifically is not used for color enhancement or as a growth inhibitor; rather, its primary purpose is related to detecting the metabolic byproducts of certain bacteria.