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Enterobacteriaceae 2

Types of Testing: Miscellaneous Tests - Single Substrate

Test NamePrinciple of TestTest MethodologyResults & 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