What is Simmons citrate 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.
What is the purpose of citrate utilization?
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.
How do you perform Simmons citrate test?
Procedure
- Obtain a slant of Simmons Citrate Agar.
- Using an inoculating needle, stab your assigned organism into the medium, then zigzag the needle back and forth up the surface of the slant.
- Incubate the tube for at least 48 hours.
- After the incubation period, examine the slant.
What indicates a positive Simmons citrate 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.
What bacteria can use citrate?
Klebsiella pneumoniae and Proteus mirabilis are examples of citrate positive organisms. Escherichia coli and Shigella dysenteriae are citrate negative.
How does citrate test work?
The citrate test screens a bacterial isolate for the ability to utilize citrate as its carbon and energy source (3, 7). 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.
How does the citrate test work?
What is the medical or diagnostic significance of citrate utilization test quizlet?
what is the purpose of the citrate utilization test? -the purpose of the citrate utilization test is to identify intestinal bacteria that are capable of using citrate as their sole carbon source. -this ability depends on the production of an enzyme called citrate permease.
What color does the citrate test turn if it is positive?
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. Therefore conversion of the medium to blue is a positive citrate test result.
Can E. coli eat citrate?
E. coli doesn’t normally eat citrate unless it is desperate (there’s no glucose, no oxygen). But these E. coli did evolve the ability to eat citrate, in fact thrive on it, in the presence of both oxygen and glucose.
Can E. coli utilize citrate?
It is well known that wild-type E. coli cannot use citrate as a carbon source, aerobically, because it lacks a citrate transporter, but can use citrate under anaerobic conditions via expression of the CitT citrate/succinate antiporter (5,–9).
What type of indicator does the citrate test use quizlet?
-we can detect the use of citrate using a citrate agar slant containing sodium citrate and the pH indicator bromothymol blue.
How does Sim medium detect motility?
SIM medium is used to detect motility by observing the growth of bacteria from the initial stab. Growth that radiates out from initial stab means that the bacteria are more motile. If growth remains in a straight line around stab, bacteria ARE NOT motile.
What grows on Simmons Citrate agar?
Principle of Simmons Citrate agar. Bacteria that can utilize citrate as the sole carbon source and inorganic ammonium salt as the sole source of nitrogen grow on this medium.
How do you read a citrate test?
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.
Is E. coli citrate positive or negative?
citrate negative
Escherichia coli and Shigella dysenteriae are citrate negative.
What organisms can utilize citrate as sole source of carbon?
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.
What is the purpose of Simmons citrate test quizlet?
What is the purpose of the Citrate test? The citrate test determines if an MO uses citrate as a sole source of carbon.
How do you use SIM Agar?
Procedure
- Obtain a deep of SIM medium.
- Using an inoculating needle, stab the medium about 2/3 of the way down and out the same pathway as quickly as possible with your assigned organism.
- Incubate the tube for at least 48 hours.
- After the incubation period, examine your tube.