|Hydrogen Sulfide Production
Some bacteria have the enzymatic capability to degrade amino acids (cysteine, cystine etc.) that contain sulfhydryl
group (-SH) producing hydrogen sulfide. Hydrogen sulfide reacts with heavy metals such as lead or iron forming a
black precipitate. You can use TSI medium (contains iron) or prepare a nutritive agar with lead acetate (1g Pb
acetate to 100 ml nutritive agar).
Peptic peptone 10g, Casein peptone 10g, Meat extract 3g, Yeast extract
3g, Lactose 10g, Sacharose 10g, Dextrose 1g, NaCl 5g, Fe2SO4 0.2g,
Na-thyosulphate 0.3g, Phenol red 0.024g, Agar 12g, H2O ad 1000 ml.
Harvest a well isolated colony and inoculate a TSI tube by stabbing the
medium. Incubate at 37 °C, 24 hours. Reaction is positive if a black color
Bacteria growing in TSI degrade aminoacids forming ferrous sulfide which
blackens the medium.
1. H. Raducanescu, V.Bica-Popii,1986. Bacteriologie veterinara, Ed. Ceres, Bucuresti.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown Publishers.
|TSI Medium blackening due to H2S production
(left tube) - Salmonella choleraesuis
(c) Costin Stoica