Which organism is positive for citrate?
Klebsiella pneumoniae and Proteus mirabilis are examples of citrate positive organisms.
What does a positive result indicate in the citrate test?
A positive result is color change from green to blue and/or growth. This means that citrate is utilized. Bacteria that use citrate converts the ammonium which alkalizes the agar. Therefore the dye changes from pH of 6.9 to 7.6 (acidic to alkaline) and the green dye indicates the pH going up by its color change to blue.
What type of bacteria grow on citrate?
Positive growth (i.e. citrate utilisation) produces an alkaline reaction and changes the colour of the medium from green to bright blue. Examples: Serratia and the majority of the Enterobacter, Citrobacter, Klebsiella, Proteus and Providencia species, except Morganella morganii and Klebsiella rhinoscleromatis.
Is Salmonella citrate positive?
When Simmons Citrate agar is inoculated with Salmonella typhimurium , the medium turns royal blue. This is a positive result for the citrate test.
What is the purpose of citrate?
The citrate test is performed along with the other IMViC tests to differentiate Gram-negative bacilli of the Enterobacteriaceae family. It is an important test that allows the species-level identification of the members of the Enterobacteriaceae family.
What color is positive citrate test?
blue
If the medium turns blue, the organism is citrate positive. If there is no color change, the organism is citrate negative.
What is citrate agar used for?
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. It is used for differentiating gram-negative bacteria on the basis of citrate utilization.
Why is E. coli citrate negative?
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-negative test culture will be virtually indistinguishable from an uninoculated slant. E. coli is citrate negative.
How does citrate test work?
At pH 7.5 or above, bromthymol blue turns royal blue. At a neutral pH, bromthymol blue is green, as evidenced by the uninoculated media. If the medium turns blue, the organism is citrate positive. If there is no color change, the organism is citrate negative.
Why is the citrate test important?
The citrate test detects the ability of an organism to use citrate as the sole source of carbon and energy.