The oxidase test is a wonky biochemical test keep

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The Oxidase Test is a wonky Biochemical Test. Keep this in Mind if you get goofy F Agar or IMViC Results. F Agar (Fluorescence Agar) “Does this Bacterium produce fluorescent Siderophores?” Some species of Pseudomonas secrete the fluorescent, Water-soluble Pigments Pyocyanin (G= blue-green pus) and Pyoverdin (G= green pus) , which fluoresce Blue- Green and Green, respectively under Ultraviolet Light (or even under the Fluorescent Lights in the Lab). These Pigments are termed Siderophores (G= star [iron] holders) and they are Chelating Agents (G= claw) that latch onto Iron in the Environment and make it more readily available to the Bacterium. Iron is a Key Component of Cytochromes and Proteins involved in the Electron Transport Chain. Pseudomonas can be induced to produce these Pigments by Growth on an Iron-deficient Medium, such as F Agar (“F” for Fluorescence). Once you’ve demonstrated that your Pseudomonas is Oxidase Positive, go ahead and streak it onto an F Agar Plate (Brown Stripe) and incubate it at 30°C until the next Lab. A Positive -- and we’ve rarely encountered Duds in MIC 101 -- will reach out and slap you in the Face with Fluorescence next Lab. You won’t really need the UV Light to see this Fluorescence but we’ve got it in the Prep Area, just in case. F Agar is a very Reliable Medium.
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Lab 6 Page 27 The IMViC The IMViC (rhymes with Rhythmic) isn’t a Single Test but rather is a Series of Tests designed to definitively distinguish E. coli from Enterobacter . The Name is an Acronym (G= top letters) for Indole, Methyl Red, Voges-Proskauer, and Citrate, with an “i” added as a convenient Vowel. Why does the IMViC go to such Lengths to distinguish these two Bacteria? This happens to be particularly important in Water Testing. The Presence of Enterobacter in a Water Sample is no Big Deal. Enterobacter can live in the Gut of Warm Blooded Animals but it’s also a normal Inhabitant of the Soil. But E. coli cannot live outside of the Gut of a Warm Blooded Animal for very long, so its Presence is considered Positive for Fecal Contamination. E. coli itself generally isn’t all that nasty a Bacterium (although some Strains have gone over to The Dark Side) but the Presence of E. coli implies the Presence of undeniable Nasty Pathogens like Hepatitis Virus. The Results from IMViCs for E. coli and Enterobacter are neatly Reciprocal: Indole MR VP Citrate E. coli + + - - Enterobacter - - + + Indole (Atlas Page 74) “Does this Bacterium have the Enzyme Tryptophanase?” Bacteria with the Enzyme Tryptophanase can convert the Amino Acid Tryptophan to Indole, Ammonia, and Pyruvic Acid. The Pyruvic Acid can be shunted into the TCA Cycle, the Ammonia can be used in the Synthesis of Amino Acids. The Indole is actually just a By-Product of this Reaction.
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