|TSI Medium blackening due to H2S production
False-positive H2S production on TSI medium (left).
Test checks simultaneously for the production of hydrogen sulfide, acid fermentation
of lactose, sacharose, glucose and gas production from glucose. Medium, together
with MIU and Simmons agar, is most used for Enterobacteriaceae identification,
especially Escherichia and Salmonella.
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.
Pour the medium filling the bottom half of the tube and creating a slant in the upper
Harvest a well isolated colony and inoculate a TSI tube by stabbing the medium then
zigzag streaking on the surface of the slant. Incubate at 37 °C, 24 hours.
H2S production: positive if a black precipitate of iron sulfide forms.
Lactose / sacharose fermentation: positive for yellow color of slant and negative for
Glucose fermentation: positive if medium changes to yellow, negative if no changes
Gas production: gas bubbles captured in the bottom part of the medium are
observed. Sometimes gas production is so high that medium is pushed up to the cap.
Do not incubate more than 24 hours. False-positive or false-negative results may
Klebsiella oxytoca strains can produce a dark brown pigment when growth on media
containing gluconate and ferric citrate. The TSI slant is darkened by pigment, not by
hydrogen sulfide production.
1. Helgomar Raducanescu, Valeria.Bica-Popii,1986. Bacteriologie veterinara, Ed.
2. Margaret Barnett, 1992. Microbiology Laboratory Exercises. Wm. C. Brown
|TSI (left), MIU and Simmons agar
(c) Costin Stoica
A demonstration of TSI, MIU and Simmons utilization is available in video section.