The
TSI-Agar
[(NH
4)2Fe(SO4)2], and sodium thiosulphate [Na2S2O3]. In actual practice TSI-Agar is solely used for
the critical identification of
enteric organisms* ; and are broadly based upon their inherent ability to
attack the chemical entities
viz., glucose, lactose, or sucrose and thus are responsible for liberating
‘sulphides’
from ferrous ammonium sulphate or sodium thiosulphate.
The various
typical examples of TSI-Agar are as stated under :
(
a) Citrate Agar. It contains sodium citrate [C6H5Na3O7], which serves as the exclusive source
of carbon
; whereas, the ammonium phosphate [(NH4)3PO4] as the sole source of nitrogen. The citrate
agar
finds its usage to differentate the ‘enteric bacteria’ on the basis of ‘citrate utilization’.
(
b) Lysine Iron Agar [LIA]. Importantly, LIA is solely employed to differentate microorganisms
which may either cause
deamination or decarboxylation the amino acid lysine. Because, LIA
comprises of
lysine that predominantly and exclusively allows enzyme detection ; whereas the presence
of
ferric ammonium citrate helps in the detection of H2S production.
(
c) Sulphide-Indole-Motility Medium [SIM-Medium]. In fact, the SIM-medium is employed
exclusively for the following
three different tests, namely :
(
i) production of sulphides,
(
ii) formation of indole
NH
i.e.
, a metabolite product duly obtained from the subsequentutilization of tryptophan, and
(
iii) causation of ‘motility’.
Precisely, the
SIM-Medium is used for making out the differentiation of the various entericorganisms.