citrate test. [′si‚trāt ‚test] (microbiology) A differential cultural test to identify genera within the bacterial family Enterobacteriaceae that are able to utilize sodium citrate as a sole source of carbon.
What is the principle of the citrate test?
Principle of Citrate Test. A citrate test or citrate utilization test is used to determine the ability of an organism to utilize sodium citrate as its only carbon source and inorganic ammonium salts as its only nitrogen source. When the bacteria metabolize citrate, the ammonium salts are broken down to ammonia, which increases alkalinity turning the bromthymol blue indicator from green to blue.
What is the positive organism for citrate utilization test?
Simmons citrate agar tests the ability of organisms to utilize citrate as a carbon source. If the medium turns blue, the organism is citrate positive. If there is no color change, the organism is citrate negative. Hereof, what bacteria are citrate positive? Klebsiella pneumoniae and Proteus mirabilis are examples of citrate positive organisms.
What is a citrate test?
The citrate test screens a bacterial isolate for the ability to utilize citrate as its carbon and energy source. A positive diagnostic test rests on the generation of alkaline by-products of citrate metabolism. The subsequent increase in the pH of the medium is demonstrated by the color change of a pH indicator.
What does the citrate metabolic test test for?
Citrate utilization test is commonly employed as part of a group of tests, the IMViC (Indole, Methyl Red, VP and Citrate) tests, that distinguish between members of the Enterobacteriaceae family based on their metabolic by-products. Citrate utilization can be used to distinguish between coliforms such as Klebsiella (formerly Enterobacter) aerogenes (+ve) which occur naturally in the soil and ...
What is citrate used for in bacteria?
Citrate is a ubiquitous natural compound which can be utilized as a carbon and energy source by many bacterial species.
What enzyme is the citrate test used to detect?
This test is part of the IMViC tests and is helpful in differentiating the Enterobacteriaceae . Organisms which can utilize citrate as their sole carbon source use the enzyme citrase or citrate-permease to transport the citrate into the cell.
Which organism is citrate test positive?
Klebsiella pneumoniae and Proteus mirabilis are examples of citrate positive organisms. Escherichia coli and Shigella dysenteriae are citrate negative.
What is citric test?
Citric acid urine test measures the level of citric acid in urine.
What is the principle of citrate test?
Principle of Citrate Utilization Test Citrate agar is used to test an organism's ability to utilize citrate as a source of energy. The medium contains citrate as the sole carbon source and inorganic ammonium salts (NH4H2PO4) as the sole source of nitrogen.
Which media is used for citrate test?
Simmon's Citrate agar is used as the medium to test the ability of an organism to utilize citrate as a sole source of energy.
Why is the citrate test used?
Citrate testing is used to determine the ability of the bacteria to use sodium citrate as the only source of carbon and inorganic ammonium hydrogen phosphate (NH4H2PO4) as a source of nitrogen. The citrate utilization test is possible only if the organisms are capable of fermenting citrate.
What does a negative citrate test indicate?
Citrate negative: trace or no growth will be visible. No color change will occur; the medium will remain the deep forest green color of the uninoculated agar. Only bacteria that can utilize citrate as the sole carbon and energy source will be able to grow on the Simmons citrate medium.
Is citrate test selective or differential?
Simmons citrate agar is a selective and differential medium that tests for an organism's ability to use citrate as a sole carbon source and ammonium ions as the sole nitrogen source.
Which broth is used for citrate test?
Simmons Citrate Agar is an agar medium used for the differentiation of Enterobacteriaceae based on the utilization of citrate as the sole source of carbon....Ingredients per liter of deionized water:*IngredientsSodium Chloride (NaCl)5.0 gmSodium Citrate (dehydrate)2.0 gmAmmonium Dihydrogen Phosphate1.0 gm4 more rows•Aug 10, 2022
How do you test for citric acid?
The test is carried out by neutralising the citric acid to phenolphthalein, adding 10 C.C. of the reagent, diluting to about 200 C.C. with water, and boiling for 3 hours. In the presence of citric acid a grey-white turbidity or precipitate is obtained depending on the amount of acid present.
Which bacteria is indole positive?
Indole-Positive Bacteria Bacteria that test positive for cleaving indole from tryptophan include: Aeromonas hydrophila, Aeromonas punctata, Bacillus alvei, Edwardsiella sp., Escherichia coli, Flavobacterium sp., Haemophilus influenzae, Klebsiella oxytoca, Proteus sp.
What does the indole test test for?
The indole test screens for the ability of an organism to degrade the amino acid tryptophan and produce indole. It is used as part of the IMViC procedures, a battery of tests designed to distinguish among members of the family Enterobacteriaceae.
Is the citrate test selective or differential?
Simmons citrate agar is a selective and differential medium that tests for an organism's ability to use citrate as a sole carbon source and ammonium ions as the sole nitrogen source.
Which of the following enzymes is responsible for indole production in the Sims test?
The enzyme responsible for this process is thiosulfate reductase. What are the parts of the reaction? What is added after incubation for the indole production? A student inoculated SIM tube for a hydrogen sulfide production test.
What is the purpose of the phenylalanine test?
Serum phenylalanine screening is a blood test to look for signs of the disease phenylketonuria (PKU). The test detects abnormally high levels of an amino acid called phenylalanine.
Principle of Citrate Utilization Test
Citrate agar is used to test an organism’s ability to utilize citrate as a source of energy. The medium contains citrate as the sole carbon source...
Media Used in Citrate Utilization Test
CompositionDeionized water = 1,000 mlFinal pH 6.9 +/- 0.2 at 25 degrees C.Preparation 1. Dissolve above salts in deionized water. 2. Adjust pH to 6...
Procedure of Citrate Utilization Test
1. Streak the slant back and forth with a light inoculum picked from the center of a well-isolated colony. 2. Incubate aerobically at 35 to 37C fo...
Quality Control of Citrate Utilization Test
Citrate Positive: Klebsiella pneumoniae ATCC 13883 (growth; blue color)Citrate Negative: Escherichia coli ATCC 25922 (no growth or trace of growth)
What is citrate testing?
Citrate testing is used to determine the ability of the bacteria to use sodium citrate as the only source of carbon and inorganic ammonium hydrogen phosphate (NH4H2PO4) as a source of nitrogen. The citrate utilization test is possible only if the organisms are capable of fermenting citrate. The process takes place via the enzymes is called citrase.
What happens to citrate after it is absorbed?
Upon cell absorption of citrate, it is cleaved into oxaloacetate and acetate by the citrate lyase. Oxaloacetate is further metabolized to carbon dioxide and pyruvate. After the formation of pyruvic acid metabolic degradation depends on the pH of the solution. 1.
What is bromothymol blue?
Bromothymol blue is considered as a pH indicator. For the citrate utilization test oxygen is required and the process is done on the slants. The citrate is oxidized from bacteria and is extracted with the release of CO2 from the medium.
How long to incubate Simmons citrate agar?
In the citrate medium, organisms require more time to grow. Therefore, the solution must be incubated at 35°C to 37°C for 18 – 24 hours.
What is the product of sodium citrate?
Sodium from sodium citrate combines with CO 2 and water, to form an alkaline product (sodium carbonate).
Is sodium citrate a carbon source?
Sodium citrate is considered as both a carbon source and an energy source. Nitrogen source is NH 4+. The presence of enzymes such as citrate permease (citrase) facilitates the citrate into the bacterium. Bromothymol blue is considered as a pH indicator.
What is citrate test?
Citrate test is used to determine the ability of an organism to utilize citrate as a sole source of energy. A citrate test is performed as a part of the IMViC test to differentiate members of Enterobacteriaceae. The test is also used for the differentiation between fecal coli and members of the aerogenes group on the basis of citrate utilization.
What is the test called for citrate?
The test is also called Simmon’s citrate test as it utilizes Simmon’s citrate agar that contains citrate as the major source of energy.
What is Citrate Utilization Test?
The citrate utilization test is a part of the IMViC test ( Indole, Methyl Red, Vogues-Proskauer, and Citrate Test) that differentiates organisms on the basis of their ability to use citrate as a sole source of energy.
What is the principle of citrate utilization?
Principle of Citrate Utilization Test. Citrate agar is used to test the ability of an organism to utilize citrate as a source of energy. The agar medium contains citrate as the sole carbon source and inorganic ammonium salts as the sole source of nitrogen. The growth of the organism is indicative of the utilization of citrate as it is an ...
What is the enzyme that breaks down citrate?
The growth of the organism is indicative of the utilization of citrate as it is an intermediate metabolite in the Krebs cycle. The enzyme citrase breaks down citrate into oxaloacetate and acetate, where oxaloacetate is further broken down to form pyruvate and carbon dioxide.
What is a positive citrate test?
A positive test is demonstrated by growth with a color change from green to intense blue along the slant. A negative test is demonstrated by no growth and no color change, and the color of the slant remains green. The following table demonstrates the result of Citrate utilization of important medical bacteria: 1.
What is the result of citrate metabolism?
The growth of the organism on the medium followed by the change in the color; as a result, of citrate metabolism gives a positive citrate test.
What does a citrate test show?
Citrate test positive: The growth will be visible on the slant surface and the medium will be an intense blue. The alkaline carbonates and bicarbonates produced as by-products of citrate catabolism raise the pH of the medium to above 7.6, causing the bromothymol blue to change from the original green color to blue.
What is citrate utilization test?
A citrate test or citrate utilization test is used to determine the ability of an organism to utilize sodium citrate as its only carbon source and inorganic ammonium salts as its only nitrogen source. When the bacteria metabolize citrate, the ammonium salts are broken down to ammonia, which increases alkalinity turning the bromthymol blue indicator from green to blue.
Is Escherichia coli citrate positive?
As you know, Escherichia coli is citrate utilization test negative; although uncommon, natural E. coli variants that are citrate positive have been isolated. Citrate-negative strains of E. aerogenes have also been found.
Is the reaction of this medium alone sufficient for identification at the species level?
The reaction of this medium alone is not sufficient for identification at the species level.
Can citrate be used as a negative?
Citrate test negative: trace or no growth will be visible. No color change will occur; the medium will remain the green color of the uninoculated agar. Only bacteria that can utilize citrate as the sole carbon and energy source will be able to grow on the Simmons citrate medium, thus a citrate utilization negative test culture will be virtually indistinguishable from an uninoculated slant.
What is the enzyme used to transport citrate into the cell?
Organisms which can utilize citrate as their sole carbon source use the enzyme citrase or citrate-permease to transport the citrate into the cell. These organisms also convert the ammonium dihydrogen phosphate to ammonia and ammonium hydroxide, which creates an alkaline environment in the medium.
What is the purpose of Simmons citrate agar?
Simmons citrate agar tests the ability of organisms to utilize citrate as a carbon source. Simmons citrate agar contains sodium citrate as the sole source of carbon, ammonium dihydrogen phosphate as the sole source of nitrogen, other nutrients, and the pH indicator bromthymol blue.
Which enzyme transports citrate into the cell?
for bacteria that possess the enzyme citrate permease to transport citrate into the cell and metabolize it by way of the fermentation pathway.
Is citrate a postive test?
citrate is being utilized and is considered a postive test result. use an inoculating needle
What is the purpose of the test?
The purpose is to see if the microbe can use the compound citrate as its sole source of carbon and energy for growth.
How is citrate use determined?
If a microbe can use citrate for carbon and energy, it will grow on Simmons citrate agar. The use of citrate leads to a rise in pH of the medium, and a pH indicator changes color.
What medium is used?
The medium used is Simmons citrate agar slant. It contains mineral salts, sodium citrate for carbon, and ammonium phosphate for its nitrogen source. The pH indicator is brom thymol blue, which is green at neutral pH, yellow at acidic pH <6.0 and turns blue at alkaline (basic) pH >7.6.
How is the test performed?
An inoculum from a pure culture is transferred aseptically to a sterile tube of Simmons citrate agar. The inoculated tube is incubated at 35-37 C for 24 hours and the results are determined. Abundant growth on the slant and a change from green to blue in the medium indicates a positive test for growth using citrate.
