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Enterobacteriaceae 2
Types of Testing: Miscellaneous Tests - Single Substrate
| Test Name | Principle of Test | Test Methodology | Results & Interpretation |
|---|---|---|---|
| Urease Test | Urease hydrolyzes the substrate urea into ammonia, water, and CO2 / ammonia raises pH = pH indicator | media infused with phenol red (pH indicator) to detect the ammonia given off in the hydrolyze reaction of Urea by urease | Pink color = positive result / no color change = negative result |
| Citrate Test | determine if a bacterium can grow using citrate as its sole carbon and energy source | Indicator dye (bromthymol blue) added, blue at alkaline pH, yellow at acidic pH / citrate media, not yet inoculated, is neutral pH & a green color / use of carbon as energy source = alkaline pH | Green color = negative result / Prussian blue color = positive result |
| Malonate Test | determine if organism is capable of using sodium malonate as its sole carbon source | Indicator dye (bromthymol blue) added as pH indicator / bacteria able to use malonate as sole carbon source will also use ammonium sulfate as a nitrogen source = create a alkaline environment | Green color = negative result / Blue color = positive result |
| Nitrate/Nitrite Reaction | determine if organism can reduce nitrate to nitrite and further reduce nitrite to nitrogen gas | Organism inoculated into broth containing a nitrogen source, after 18-24 hours the tubes are read for presence or absence of three metabolic product (Nitrogen gas, Nitrite, & Nitrate) | Presence of gas after organism is incubated / Nitrate reduced to Nitrite = 2 reagents added - red color = positive result / Nitrite reduction to Nitrogen gas - no color then red after reagents added & gas produced = positive result |
| Oxidase Test | pivotal test = performed on most Gram negative organisms / Cytochrome oxidase reaction for electron transfer to oxygen | If bacteria oxidize the reagent (remove electrons), a purple color will form or no color change will occur | Purple color = positive / no color change = negative / most normal enteric GNR are oxidase negative (Ex - E. coli) / Psudomonas species are oxidase positive |
| indole Test | some bacteria break down tryptophan for nutrition using tryptophanase | when tryptophan is broken down, presence of indole (amino acid in tryphophan) can be detected by Kovac's reagent | Red color on surface = positive result / yellow color on surface = negative result |
Created by:
nbechen3
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