SIM Medium and Biochemical Tests Flashcards

Vocabulary flashcards covering Sulfur reduction, Indole production, and Motility (SIM) tests, key endoenzymes, chemical reactions, and experimental results.

SIM Medium

A combination differential medium used in microbiology to evaluate three bacterial traits: Sulfur reduction, Indole production, and Motility.

SIM Recipe Components

The formulation of SIM agar consisting of pancreatic digest of casein (providing cysteine and tryptophan), ferrous ammonium sulfate, sodium thiosulfate, and a low concentration of agar.

Motility Test (SIM)

A test measuring bacterial movement in a semi-solid medium; positive results show turbidity spreading throughout the medium away from the stab line, whereas negative results show growth restricted strictly to the stab line.

Cysteine Desulfurase

An endoenzyme that catalyzes the hydrolysis of the amino acid cysteine to yield hydrogen sulfide gas ($H_2S$), ammonia ($NH_3$), and pyruvate.

Thiosulfate Reductase

An endoenzyme active in anaerobic respiration that reduces sodium thiosulfate ($3S_2O_3^{2-}$) at the end of the electron transport chain to produce sulfite ($2SO_3^{2-}$) and hydrogen sulfide gas ($2H_2S$).

Ferrous Ammonium Sulfate

An indicator included in SIM medium that reacts with hydrogen sulfide ($H_2S$) gas produced by bacterial sulfur reduction to form a black precipitate.

Sulfur Reduction Test (SIM Results)

A test detecting hydrogen sulfide ($H_2S$) production; a positive result ($S^+$) produces blackening throughout the medium, while a negative result ($S^-$) shows no blackening.

Tryptophanase

An endoenzyme produced by certain bacteria that hydrolyzes the substrate tryptophan into indole, ammonia ($NH_3$), and pyruvate.

Kovacs Reagent

A chemical reagent added to SIM medium after incubation that reacts with indole to produce a red or pink ring at the surface of the medium.

Indole Test (SIM Results)

A test assessing tryptophan degradation; addition of Kovacs Reagent yields a red/pink top layer for a positive result ($I^+$) and an unchanged yellow layer for a negative result ($I^-$).

Cysteine Desulfurase Reaction Pathway

The enzymatic pathway in which cysteine (substrate) plus water and $H^+$ is broken down by cysteine desulfurase (endoenzyme) into hydrogen sulfide ($H_2S$) gas, ammonia ($NH_3$), and pyruvate.

Thiosulfate Reductase Reaction Pathway

The anaerobic respiration pathway where sodium thiosulfate ($3S_2O_3^{2-}$) is reduced by thiosulfate reductase (endoenzyme) in the electron transport chain to produce sulfite ($2SO_3^{2-}$) and hydrogen sulfide gas ($2H_2S$).

Tryptophanase Reaction Pathway

The reaction pathway where tryptophan (substrate) reacts with water via tryptophanase (endoenzyme) to form indole (byproduct), ammonia ($NH_3$), and pyruvate.