Quiz On Urease And Sims Flashcards
What is urea?
The primary nitrogenous waste in the urine of many land animals
It can be hydrolyzed to ammonia and carbon dioxide by bacteria
What process produces urea?
The decarboxylation of certain amino acids
What type of bacteria possess the ability to metabolize urea
Many enteric bacteria possess the ability
And their urease genes are activated when a usable nitrogen source is absent or urea is present
How is the current urea broth different than the old urea agar
The urea agar allowed for the testing of both rapid urea positive bacteria and slow urea positive bacteria whereas the urea broth only tests for rapid urea positive bacteria
The only nutrient source in the urea broth is a trace of yeast extract and urea
What creates the positive in the urea broth?
phenol red which turns yellow or orange below. pH. 8.4 and red or pink above is used to expose any increase or decrease in PH
How to inoculate and incubate for the urease test?
Inoculate the two urea broths with heavy inoculi incubate aerobically at 35 plus or minus 2° C for 24 hours
What does a positive urease test look like?
The broth turns pink or red
What is combination differential media and why would you use it
It combines components of several compatible tests into one medium and it saves critical diagnostic time and money
What does the SIM test test for
Sulfur reduction
Indole production
Motility
All characteristics of members of enterobacteria
What does the medium in the Sim test include?
casein and
Animal tissue as sources of amino acids
An iron containing compound
Sulfur in the form of sodium thiosulfate
How does sulfur reduction work?
Enzymes are used to produce hydrogen sulfide gas which combines with iron in the form of ferrous ammonium sulfate to form ferric acid a black precipitate
How is indole production achieved?
It is made possible by the presence of the amino acid tryptophan
Bacteria that possess the enzyme tryptophanase can hydrolyze tryptophan to pyruvate, ammonia and indole
How can tryptophan hydrolysis in the SIM medium be detected
By the addition of kovac’s reagents which contain dmaba and hydrochloric acid dissolved in amyl alcohol
What does a positive? Indole test look like
After a few drops of kovax reagent are added
If a red band forms in the covex reagent, you have a positive test
How to determine the motility of the Sim medium?
After the medium is inoculated with a single stab from an inoculating needle
Motal organisms are able to move about in the semi-solid medium and can be detected by radiating growth extending outward in all directions from a central stab line
Growth radiates in all directions and appears slightly fuzzy
What bacteria are used in the urease test versus The Sims test
The urease test uses e. Coli
P. Vulgaris
The Sims test uses e coli
M luteus
P. Mirabilis
How do you inoculate an incubate for the Sims test
You inoculate by stab technique into the agar within 1 cm of the bottom of the tube
You incubate aerobically at 35 plus or minus 2° C for 24 to 48 hours
