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Bacterial Metabolic Activities
- observing certain metabolic activities of an organism allows the microbiologist to identify its genus and species
- 3 types: Carbohydrate Fermentation/Oxidation, SIM agar, and Citrate utilization
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SIM agar
- production of H2S, Indole and Motility
- SIM agar is semi-solid agar that can be inoculated with an organism and observed for production of H2S and indole
- it also can be observed for motility
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H2S
- the SIM agar medium contains cysteine (an amino acid with sulfur) and iron (metallic ion)
- some organism can metabolize cysteine producing hydrogen sulfide gas (H2S)
- H2S combines with iron to form a black metal sulfide
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Indole
- the SIM agar also contain an amino acid called tryptophan
- some organism can metabolize tryptophan producing indole as a by-product
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Motility
the SIM agar can also be observed for motility
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Citrate Utilization of Sodium Citrate
- to determine the ability of an organism to use citrate as the sole source of carbon for metabolism and growththe medium contains bromthymol blue indicator that turns green to blue if citrate is broken down producing alkaline byproducts
- if stays green, then it is Citrate negative
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Bacterial metabolic activities
- observing metabolic activities allows the microbiologist determine Genus and species
- some bacteria ferment or oxidize carbohydrates and the end product is lactic acid
- when in a OF Glucose Media, organisms that use glucose are classified into 2 groups: Strict oxidizer or fermenter
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Strict Oxidizer
- 2 OF Media tubes are inoculated
- 1 will have mineral oil to cut off the oxygen called fermentation tube, the other does not called oxidation tube
- if after incubation, the oxidized tube turns yellow and fermentation tube turns green then it is called the Strict Oxidizer
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Fermenter
- 2 OF Media tubes are inoculated
- 1 will have mineral oil to cut off the oxygen called fermentation tube, the other does not called oxidation tube
- if after incubation, the oxidized tube turns yellow and fermentation tube turns yellow then it is called the Fermenter
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Indole +
is always Escherichia coli
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Indole +/-
can be from Pseudomonas
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spot indole
is when it is described as Gram negative rod, indole positive
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