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C-L-E-A-R bacteria: hydrogen sulfide production

Some organisms metabolize sodium thiosulfate and produce hydrogen sulfide. The hydrogen sulfide combines with ferrous sulfide in the triple sugar iron (TSI) agar to form a black to dark insoluble precipitate.

This slide shows weak hydrogen sulfide production (black precipitate) in TSI media typical of Erysipelothrix. None of the other CLEAR organisms produce hydrogen sulfide.