Is it possible to have a positive result for the citrate hydrolysis test if there is strong growth on the medium no color change provide one reason supporting your answer?
If the medium turns blue, the organism is citrate positive. If there is no color change, the organism is citrate negative. Some citrate negative organisms may grow weakly on the surface of the slant, but they will not produce a color change.
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.
Which enterobacteria is used as a +ve control in citrate utilization test?
Citrate utilization can be used to distinguish between coliforms such as Klebsiella (formerly Enterobacter) aerogenes (+ve) which occur naturally in the soil and in aquatic environments from fecal coliforms such as Escherichia coli (-ve) whose presence would be indicative of fecal contamination.
Can Enterobacter aerogenes utilize citrate?
Enterobacter species are able to utilize sodium citrate as the sole carbon source while E. Citric acid or its sodium salt is utilized as a sole source of carbon and ammonium salt as the sole source of nitrogen by E. aerogenes while E. coli does not utilize these salts and hence fail to grow.
Is Simmons citrate medium a selective medium?
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 useful for selecting organisms that use citrate as its main carbon and energy source.
How would you expect both positive and negative results to be affected if you were to add glucose?
What happens during the Starch Hydrolysis test? How would you expect both positive and negative results to be affected if you were to add glucose to the medium in the starch hydrolysis test? The glucose would cause the starch breakdown to be slower resulting in a false negativ. What is the DNA Hydrolysis DNase test?
Is the Simmons citrate agar complex or defined 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.
Which medium is used for citrate test?
Citrate agar
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.
Is Enterobacter aerogenes lactose positive?
E. aerogenes tested positive when treated with/for: Voges-Proskauer, Simmons’ citrate, KCN, Motility, Lysine decarboxylase, Ornithine decarboxylase, Gas from glucose, Lactose, Sucrose, Manntiol, Salicin, Adonitol, Inositol, Sorbitol, Arabinose, Raffinose, and Rhamnose.
Is Enterobacter aerogenes VP positive?
Note: A culture will usually only be positive for one pathway: either MR+ or VP+. Escherichia coli is MR+ and VP-. In contrast, Enterobacter aerogenes and Klebsiella pneumoniae are MR- and VP+. Pseudomonas aeruginosa is a glucose nonfermenter and is thus MR- and VP-.
Why is Simmons citrate a selective medium?
Is Simmons citrate a defined or complex medium?
Which is a positive result of the citrate utilization test?
Some organisms are capable of growth on citrate and do not produce a color change. Growth is considered a positive citrate utilization test, even in the absence of a color change. Tests with equivocal results should be repeated. The reactions of this medium alone are not sufficient for identification to the species level.
Are there any limitations to using Simmons citrate agar?
Limitations of Simmons Citrate Agar It is important not to carry over any nutrients into the citrate medium because this will result in false positive tests. Some organisms are capable of growth on citrate and do not produce a color change. Tests with equivocal results should be repeated.
How to prepare Simmon citrate for utilization test?
Prepare Simmon citrate agar or Koser’s citrate medium in test tubes, taking 5 ml medium by autoclaving at 15lbs for 15 minutes. tilt the test tube containing melted citrate medium to prepare distinct slant and butt. Inoculate the given sample of organism were on the slant of the media using sterile wire and label the tubes
Which is an example of positive growth of 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.