Ex. 21: SIM Medium (Sulfur, Indole, Motility) Objectives ?

Work in a team of two students Day 1 Materials needed per team of two students: SIM tubes (3) Materials needed per table: Three pure slant cultures, one each of: Proteus vulgaris Escherichia coli Klebsiella pneumoniae Work in a team of two students

Materials needed per 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

Table 21-1: Sulfur Reduction Results and Interpretation SIM medium after 24h incubation. Table 21-1: Sulfur Reduction Results and Interpretation Result Interpretation Symbol Black in the medium Sulfur reduction (H2S production) + No black in the medium Sulfur not reduced 

Table 21-2: Indole Production Results and Interpretation 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

Table 21-3: Motility Results and Interpretation 3. Motility Test Table 21-3: Motility Results and Interpretation Result Interpre-tation Symbol Growth radiating outward from the stab line Motile + No radiating growth Not motile 

SIM Medium The End Results and Interpretation? Tube 1: Tube 2: Tube 1:  (1) Positive for H2S, (2) Negative for Indole production, (3) Positive for motility Tube 2:  (2) Negative for H2S, (2) Positive for Indole production, (3) Undetermined motility The End