Triple Sugar Iron (TSI) agar

Agars are extracts of marine algae that has been purified and dried. The extraction in an acid solution is followed by

successive purifications in order to obtain clear gels, devoid of precipitates after sterilization and exempt from

inhibitory substances.

Agar is comprised essentially of agaraose (70 %) and of agaropectin (30 %) which form together a solid gel after

heating and cooling.

Agarose is a linear polysaccharide entirely comprised of D-galactose and of 3-6 anhydro-L-galactose linked at alpha

1-3 and beta 1-4.

Agaropectin, which the structure is similar to that of agarose, also contains groups of anionic esters linked to calcium

and to magnesium as well as organic acids (glucuronic and pyruvic).

The 3-6 anhydro-α-L-galactoside link is very sensitive at low pH, so much so that it is necessary to avoid prolonged

heating of acid media, which could lead to the depolymerization of the agar and consequently a loss of gel strength

Bacteriological agar type E is a European type agar which presents a gel strength superior to that of the type

A American agar.