What does it mean if a bacteria is citrate positive?
What does it mean if a bacteria is citrate positive?
A positive reaction shows that the organism can use citrate but not necessarily as the sole carbon source.
What indicates a positive Simmons citrate test?
When Simmons Citrate agar is inoculated with Salmonella typhimurium , the medium turns royal blue. This is a positive result for the citrate test. When Simmons Citrate agar is inoculated with Escherichia coli , the medium remains green.
What does the citrate test tell us about an organism?
The citrate test detects the ability of an organism to use citrate as the sole source of carbon and energy.
Why does a positive Simmons citrate agar result in the slant turning blue?
Growth is indicative of utilization of citrate, an intermediate metabolite in the Krebs cycle. When the bacteria metabolize citrate, the ammonium salts are broken down to ammonia, which increases alkalinity. The shift in pH turns the bromthymol blue indicator in the medium from green to blue above pH 7.6.
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.
Why is the citrate test selective?
The citrate utilization test is selective because only certain bacteria can utilize citrate in place of a fermentable carbohydrate.
What is the substrate in Simmons citrate agar?
What is the substrate for the Citrate Agar? An enzyme called citrase will catabolize the citrate into oxaloacetic acid and acetic acid. Acetic acid to CO2.
Why is Simmons citrate agar differential?
Simmons Citrate Agar is used as a differential medium for the identification of enteric bacteria by using Citrate as the sole source of carbon and Ammonium as the sole source of nitrogen.
Is Simmons citrate a defined or complex medium?
Simmon’s Citrate Agar This is a defined medium used to determine if an organism can use citrate as its sole carbon source. It is often used to differentiate between members of Enterobacteriaceae.