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Ex. 21: SIM Medium
(Sulfur, Indole, Motility)
Objectives ?

Day 1
Materials needed per team Materials needed per table:
of two students:
Three pure slant cultures, one
 SIM tubes (3)
each of:
 Proteus vulgaris
 Escherichia coli
 Klebsiella pneumoniae
Work in a team of two students
Day 2
Materials needed per team of two
students:
 The 3 incubated SIM tubes
from the last session.
Materials needed
per table:
 Kovac’s
reagent
1. Sulfur Reduction
Cysteine desulfurase releases H2S from
S-containing amino acids
Thiosulfate reductase releases H2S by
allowing S2O32- to be final electron
acceptor in anaerobic respiration
Ferrous iron salt in medium leads to visible
black precipitate (FeS) if H2S is produced
SIM medium after
24h incubation.
Table 21-1: Sulfur Reduction Results and Interpretation
Result
Interpretation
Black in the medium
Sulfur reduction (H2S
production)
No black in the medium Sulfur not reduced
Symbol
+

2. Indole Production
 See IMViC
Table 21-2: Indole Production Results and Interpretation
Result
Interpretation
Symbol
Red in the alcohol layer of
Kovac’s reagent
Tryptophan is broken down into
indole and pyruvate
+
Reagent color is unchanged
Tryptophan is not broken down into
indole and pyruvate

Before addition of
Kovac’s reagent
3. Motility Test
Table 21-3: Motility Results and
Interpretation
Result
Interpre- Symbol
tation
Growth radiating
outward from Motile
the stab line
+
No radiating
growth

Not
motile
SIM
Medium
Results and Interpretation?
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