Microbiology Lab: Citrate Utilization Test

Citrate Utilization Test
defined medium, designed to differentiate members of the Enterobacteriaceae, it tells about the ability to of organisms to use citrate as their sole carbon source and perform citrate fermentation
What will CUT not do?
it does not tell about the citric acid cycle
Defined medium
the amount and source of all ingredients are carefully controlled
What is the limit of sodium citrate in the medium?
will not support a complex, high-energy yielding respiratory process
What does sodium citrate do?
provide the means for bacterial species that possess the enzyme citrate permease to transport citrate into the cell and perform citrate fermentation
What does the bacteria have to possess in order to grow on this medium?
citrate permease
Citrate Lyase
enzyme that citrate-positive bacteria hydrolyze citrate into oxaloacetate and acetate and oxaloacetate is converted into pyruvate
Why would a citrate-positive organism grow without producing a change in color?
incomplete incubation, one should check for growth to indicate that citrate is being utilized and a positive result
CUT positive
Blue, citrate is utilized
CUT negative
No color change and no growth, citrate is not utilized